Hi Mark,
Something related to location maybe? Cyril did investigate RF from AM and HF transmiters in his area and their field strength but nothing obvious from this. His thinking maybe was something was pinging the amp to start ringing or sustained oscillation.
He was playing with some strange exotic cables too.
Maybe the amps he was using were not heavily enough compensated?
His BJT amp had a capacitor across the feedback resistor too, but the other lateral FET amp didn't and yet it showed MHz ringing as well. So I'm mystified too.
Something related to location maybe? Cyril did investigate RF from AM and HF transmiters in his area and their field strength but nothing obvious from this. His thinking maybe was something was pinging the amp to start ringing or sustained oscillation.
He was playing with some strange exotic cables too.
Maybe the amps he was using were not heavily enough compensated?
His BJT amp had a capacitor across the feedback resistor too, but the other lateral FET amp didn't and yet it showed MHz ringing as well. So I'm mystified too.
The collector base junction is of the order of a micron below the emitter, if the die cooks, the die cooks! The first thing over heating will do is allow the dopants to diffuse further in the silicon, changing the device electronic structure, and generally shorting all terminals together(*). The bond-wires may then fuse, leaving it open circuit.
(*)
The emitter dopant concentration is 2 or 3 orders of magnitude higher than the base, which is higher than the collector by 2 orders of magnitude (although the contact side of the collector is highly doped too). The EBC profile for an NPN device is typically n+/p/n- (with a layer of n+ on the collector contact).
On overheating the higher concentrations of dopant will totally dominate, so the emitter n+ will spread across the whole device active zone, and the collector contact dopant will join up with it to make a slab of very conductive n+ semiconductor. Depending on the geometry of the base contact there may be a residual p+ doped base area left, forming a pn diode. Its required to have highly doped layers directly under metal contacts so they are ohmic rather than schottky-barriers.
The (original) purpose of the Zobel network is to stabilize a CFP OPS as used in quasi-comp amps. Without the loading of the Zobel network, the CFP may oscillate using local feedback regardless of the global feedback stability. Years ago we had some quasi amp modules that oscillated when you pushed on the speaker diaphragm because the speaker back emf activated the negative CFP current. The solution was to add Zobel and R-L build-out.
The best RFI solution is add some small resistance (~100R) to any lead feedback caps to the LTP. Series resistors are the best RFI fix. Another example was RFI to the grid of a tube amp mic input. A mic input was connected directly to the grid, so a 50 Ohm RF connection rectified in the tube, but a 100K series resistor did nothing to the grid at audio frequencies but completely eliminated the RFI.
The best RFI solution is add some small resistance (~100R) to any lead feedback caps to the LTP. Series resistors are the best RFI fix. Another example was RFI to the grid of a tube amp mic input. A mic input was connected directly to the grid, so a 50 Ohm RF connection rectified in the tube, but a 100K series resistor did nothing to the grid at audio frequencies but completely eliminated the RFI.
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Its ironic that earlier tonight I was playing with a breadboarded amp which was quasi-complementary without a Zobel network and it was oscillating on the half-cycles on the CFP side. Alas the penny didn't drop (I usually include a Zobel in amp OS's, just happened to neglect it this time).
And I've dismantled that breadboard since, doh!
So I endorse this wholeheartedly. Fortunately I have another breadboarded amp front-end that's looking for an OS (the OS is quasi-comp because it uses IGBTs, and isn't dismantled yet)
The output inductor is one small consideration for stability, there are many others.
It takes some skill to design an amp that is unconditionally stable.
I'm going to read that article but did you catch the model of the amps that failed, schematic?
Last edited:
The section on this in Bob's book 2nd Edn is p527-8 Transmission Line Effects of Speaker Cables. A far end Zobel of 100 ohms plus 0.01uF series capacitor is similar to Cyri's recommendation.
Bob mentions the effect of speaker cables on stability in his 2019 BAF talk here
YouTube
from 44 mins to 47 mins, and he says
What I find perplexing about Cyril's research is that both types of amplifiers that showed ringing at a few MHz (with unterminated cables) was these amps did have L-R networks!
Cyril's injection tests showed attenuation at a few MHz was small.which means the L-R does not help much with instability from cable reflections, contrary to what is usually assumed. The inductor mainly isolates straight capacitive loads but are apparently ineffective for a complicated load like speaker cables present.
BTW has anyone read Cyrils Speaker Cable Amp Interaction article?.
Read part 1 and the bipolar amps were D. Self “Blameless” bi-polar 50 watt class B amplifier.
I'd sure like to see a schematic of his exact build, PC board and chassis (grounding) layouts.
This is from a Google search, the article mentions a 10K feeback resistor with 330R in series
with 100pF across the 10K. This has those values except for 16pF in series with 330R:
This is not the exact amp but it shows 10 turns 1" diameter for the output inductor,
I'll have to measure that but it seems too low.
Attachments
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There is also a graph that shows the impedance seen looking into an ordinary speaker cable for 3 conditions: 1) open at the far end, shorted at the far end, and terminated in about 100 ohms at the far end. The Characteristic impedance of many fairly conventional speaker cables (e.g., Zip cord) is usually on the order of 90-120 ohms. I tend to agree that the R-L network helps to isolate capacitive loads from the output stage emitter followers (or CFPs), but may not be as effective in isolating loads with potentially nasty transmission line effects.
I also believe that properly terminating the speaker cable at the far end may also reduce its tendency to act as an antenna for EMI pickup, but I have not done any experiments to back up this speculation. Another thing to note in regard to EMI pickup is that one must consider such pickup in both the differential and common mode. In the common mode, the speaker and its cable look like a fairly simple 10-foot (or so) antenna. The free-air body capacitance of the loudspeaker could also present antenna loading, further increasing the number of different possibilities. However, a conventional tower loudspeaker that I measured registered only about 50 pF.
The need for termination of the speaker cable with a Zobel (or, how much it might improve matters) will also likely depend on what is inside the loudspeaker, including effects of crossovers and voice coil incuctances. For example, if you have a non-inductive resistive attenuation pad in front of the tweeter, that may mitigate some of the transmission line effects because the speaker cable may then look less unterminated at high frequencies. There would seem to be a lot of room for experimentation here
.I would love to have a better understanding of why some speaker cables are perceived to sound different from others (apart from gross shortcomings or deliberate introduction of elements that alter frequency response) that is based on some valid scientific reason as opposed to marketing snake oil.
Cheers,
Bob
Usually, such tests are done sighted and that is why they "sound" different. Of course cables
that blow up amps might sound different but I'd call those bad cables.
John Dunlavy did some interesting tests and wrote about them on the net, I'll try to find it.
He ended up producing speaker cables with IIRC low Z0 and terminations but he said he
did it because it was technically correct, not because they sounded different. He sold them
because his customers wanted "high quality" cables but IIRC made no claims that they
sounded different.
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I have to look for parts 2-4 but here's the first part, I think this was originally posted on
the bass list in the mid 1990s:
"Cable Nonsense" by John Dunlavy:
Here's the first in a four part series "Cable nonsense" that John Dunlavy posted to the rec.audio.high-end newsgroup:
I'll post parts 2-4 if there is interest.
From 102365.2026@compuserve.com Tue Nov 11 12:47:34 1997
Newsgroups: rec.audio.high-end
Subject: Cable nonsense -- article #1
From: John Dunlavy <102365.2026@compuserve.com>
Date: 11 Nov 1997 13:47:34 -0500
Having read some of the recent comments on rec.audio.opinion and high end,
concerning "audible" differences between interconnect and loudspeaker cables, I
could not resist adding some thoughts about the subject as a concerned engineer
possessing credible credentials.
To begin, several companies design and manufacture loudspeaker and interconnect
cables which they proudly claim possess optimized electrical properties for the
audiophile applications intended. However, accurate measurements of several
popularly selling cables reveal significant differences that call into question
the technical goals of their designer. These differences also question the
capability of the companies to perform accurate measurements of important cable
performance properties. For example, any company not possessing a precision
C-L-R bridge, a Vector Impedance Meter, a Network Analyzer, a precision waveform
and impulse generator, wideband precision oscilloscopes, etc., probably needs to
purchase them if they are truly serious about designing audio cables that
provide premium performance.
The measurable properties of loudspeaker cables that are important to their
performance include characteristic impedance (series inductance and parallel
capacitance per unit length), loss resistance (including additional resistance
due to skin-effect losses versus frequency), dielectric losses versus frequency
(loss tangent, etc.), velocity-of-propagation factor, overall loss versus
frequency into different impedance loads, etc.
Measurable properties of interconnect cables include all of the above, with the
addition of those properties of the dielectric material that contribute to
"microphonic noise" in the presence of ambient vibration, noise, etc. (in
combination with a "D.C. off-set" created by a pre-amp output circuit, etc.).
While competent cable manufacturers should be aware of these measurements and
the need to make them during the design of their cables, the raw truth is that
most do not! Proof of this can be found in the absurd buzzard-salve, snake-oil
and meaningless advertising claims found in almost all magazine ads and product
literature for audiophile cables. Perhaps worse, very few of the expensive,
high-tech appearing cables we have measured appear to have been designed in
accordance with the well-known laws and principles taught by proper physics and
engineering disciplines. (Where are the costly Government Consumer Protection
people who are supposed to protect innocent members of the public by identifying
and policing questionable performance claims, misleading specifications, etc.?)
--- Caveat Emptor!
For example, claiming that copper wire is "directional", that slow-moving
electrons create distortion as they haphazardly carry the signal along a wire,
that cables store and release energy as signals propagate along them, that a
"final energy component" (improperly labeled as "Joules") is the measure of the
tonality of cables, ad nauseum, are but a few of the non-entities used in
advertisements to describe "cable performance".
Another pet peeve of mine is the concept of a "special configuration" included
with a loudspeaker cable which is advertised as being able to "terminate the
cable" in a matter intended to deliver more accurate tonality, better imaging,
lower "noise", etc. The real truth is that this "special configuration" contains
nothing more than a simple, inexpensive network intended to prevent
poorly-designed amplifiers, with a too-high slew-rate (obtained at the expense
of instability caused by too much inverse-feedback) from oscillating when
connected to a loudspeaker through a low-loss, low-impedance cable. When this
"box" appears at the loudspeaker-end of a cable, it seldom contains nothing more
than a "Zobel network", which is usually a "series resistor-capacitor" network,
connector in parallel with the wires of the cable. If it is at the amplifier-end
of the cable, it is probably either a "parallel resistor-inductor" network,
connected in series with the cable conductors (or a simple cylindrical ferrite
sleeve covering both conductors). But the proper place for such a network, if it
is needed to "insure amplifier stability and prevent high-frequency
oscillations", is within the amplifier - not along the loudspeaker cable. Hmmm!
Having said all this, are there really any significant "audible" differences
between most cables that can be consistently identified by experienced
listeners? The answer is simple: very seldom! Those who claim otherwise do not
fully grasp the power of the old "Placebo-Effect" - which is very alive and well
among even the most well-intentioned listeners. The placebo-effect renders
"audible signatures" easy to detect and describe - if the listener knows which
cable is being heard. But, take away this knowledge during blind or double-blind
listening comparisons and the differences either disappear completely or hover
close to the level of random guessing. Speaking as a competent professional
engineer, designer and manufacturer, nothing would please me and my company's
staff more than being able to design a cable which consistently yielded a
positive score during blind listening comparisons against other cables. But it
only rarely happens - if we wish to be honest!
Oh yes, we have heard of golden-eared audiophiles who claim to be able to
consistently identify "huge, audible differences" between cables. But when these
experts have visited our facility and were put to the test under
carefully-controlled conditions, they invariably failed to yield a score any
better than "chance". For example, when led to believe that three popular cables
were being compared, varying in size from a high-quality 12 AWG ZIP-CORD to a
"high-tech looking" cable with a diameter exceeding an inch, the largest and
sexiest looking cable always scored best - even though the CABLES WERE NEVER
CHANGED and they listened to the ZIP Cord the entire time.
Sorry, but I do not buy the claims of those who say they can always audibly
identify differences between cables, even when the comparisons are properly
controlled to ensure that the identity of the cable being heard is not known by
the listener. We have accomplished too many "true blind comparisons" with
listeners possessing the right credentials, including impeccable hearing
attributes, to know that "real, audible differences" seldom exist - if the
comparisons are properly implemented to eliminate other causes such as system
interactions with cables, etc.
Indeed, during these "comparisons" (without changing cables), some listeners
were able to describe in great detail the "big differences" they thought they
heard in bass, high-end detail, etc. (Of course, the participants were never
told the "NAUGHTY TRUTH", lest they become an enemy for life!)
So why does a reputable company like DAL engage in the design and manufacture of
audiophile loudspeaker cables and interconnects? The answer is simple: Since
significant measurable differences do exist and because well-known and
understood transmission line theory defines optimum relationships between such
parameters as cable impedance and the impedance of the load (loudspeaker), the
capacitance of an interconnect and the input impedance of the following stage,
why not design cables that at least satisfy what theory has to teach? And, since
transmission line theory is universally applied, quite successfully, in the
design of cables intended for TV, microwave, telephone, and other critical
applications requiring peak performance, etc., why not use it in designing
cables intended for critical audiophile applications? Hmmm! To say, as some do,
that there are factors involved that competent engineers and scientists have yet
to identify is utter nonsense and a cover-up for what should be called "pure
snake oil and buzzard salve" - in short, pure "fraud". If any cable
manufacturer, writer, technician, etc. can identify such an audible design
parameter that cannot be measured using available lab equipment or be described
by known theory, I can guarantee a nomination for a "Nobel Prize".
Anyway, I just had to share some of my favorite Hmmm's, regarding cable myths
and seemingly fraudulent claims, with audiophiles on the net who may lack the
technical expertise to separate fact from fiction with regard to cable
performance. I also welcome comments from those who may have other opinions or
who may know of something I might have missed or misunderstood regarding cable
design, theory or secret criteria used by competitors to achieve performance
that cannot be measured or identified by conventional means. Lets all try to get
to the bottom of this mess by open, informed and objective inquiry.
I sincerely believe the time has come for concerned audiophiles, true engineers,
competent physicists, academics, mag editors, etc. to take a firm stand
regarding much of this disturbing new trend in the blatantly false claims
frequently found in cable advertising. If we fail to do so, reputable designers,
engineers, manufacturers, magazine editors and product reviewers may find their
reputation tarnished beyond repair among those of the audiophile community we
are supposed to serve.
Best Regards, John Dunlavy
the bass list in the mid 1990s:
"Cable Nonsense" by John Dunlavy:
Here's the first in a four part series "Cable nonsense" that John Dunlavy posted to the rec.audio.high-end newsgroup:
I'll post parts 2-4 if there is interest.
From 102365.2026@compuserve.com Tue Nov 11 12:47:34 1997
Newsgroups: rec.audio.high-end
Subject: Cable nonsense -- article #1
From: John Dunlavy <102365.2026@compuserve.com>
Date: 11 Nov 1997 13:47:34 -0500
Having read some of the recent comments on rec.audio.opinion and high end,
concerning "audible" differences between interconnect and loudspeaker cables, I
could not resist adding some thoughts about the subject as a concerned engineer
possessing credible credentials.
To begin, several companies design and manufacture loudspeaker and interconnect
cables which they proudly claim possess optimized electrical properties for the
audiophile applications intended. However, accurate measurements of several
popularly selling cables reveal significant differences that call into question
the technical goals of their designer. These differences also question the
capability of the companies to perform accurate measurements of important cable
performance properties. For example, any company not possessing a precision
C-L-R bridge, a Vector Impedance Meter, a Network Analyzer, a precision waveform
and impulse generator, wideband precision oscilloscopes, etc., probably needs to
purchase them if they are truly serious about designing audio cables that
provide premium performance.
The measurable properties of loudspeaker cables that are important to their
performance include characteristic impedance (series inductance and parallel
capacitance per unit length), loss resistance (including additional resistance
due to skin-effect losses versus frequency), dielectric losses versus frequency
(loss tangent, etc.), velocity-of-propagation factor, overall loss versus
frequency into different impedance loads, etc.
Measurable properties of interconnect cables include all of the above, with the
addition of those properties of the dielectric material that contribute to
"microphonic noise" in the presence of ambient vibration, noise, etc. (in
combination with a "D.C. off-set" created by a pre-amp output circuit, etc.).
While competent cable manufacturers should be aware of these measurements and
the need to make them during the design of their cables, the raw truth is that
most do not! Proof of this can be found in the absurd buzzard-salve, snake-oil
and meaningless advertising claims found in almost all magazine ads and product
literature for audiophile cables. Perhaps worse, very few of the expensive,
high-tech appearing cables we have measured appear to have been designed in
accordance with the well-known laws and principles taught by proper physics and
engineering disciplines. (Where are the costly Government Consumer Protection
people who are supposed to protect innocent members of the public by identifying
and policing questionable performance claims, misleading specifications, etc.?)
--- Caveat Emptor!
For example, claiming that copper wire is "directional", that slow-moving
electrons create distortion as they haphazardly carry the signal along a wire,
that cables store and release energy as signals propagate along them, that a
"final energy component" (improperly labeled as "Joules") is the measure of the
tonality of cables, ad nauseum, are but a few of the non-entities used in
advertisements to describe "cable performance".
Another pet peeve of mine is the concept of a "special configuration" included
with a loudspeaker cable which is advertised as being able to "terminate the
cable" in a matter intended to deliver more accurate tonality, better imaging,
lower "noise", etc. The real truth is that this "special configuration" contains
nothing more than a simple, inexpensive network intended to prevent
poorly-designed amplifiers, with a too-high slew-rate (obtained at the expense
of instability caused by too much inverse-feedback) from oscillating when
connected to a loudspeaker through a low-loss, low-impedance cable. When this
"box" appears at the loudspeaker-end of a cable, it seldom contains nothing more
than a "Zobel network", which is usually a "series resistor-capacitor" network,
connector in parallel with the wires of the cable. If it is at the amplifier-end
of the cable, it is probably either a "parallel resistor-inductor" network,
connected in series with the cable conductors (or a simple cylindrical ferrite
sleeve covering both conductors). But the proper place for such a network, if it
is needed to "insure amplifier stability and prevent high-frequency
oscillations", is within the amplifier - not along the loudspeaker cable. Hmmm!
Having said all this, are there really any significant "audible" differences
between most cables that can be consistently identified by experienced
listeners? The answer is simple: very seldom! Those who claim otherwise do not
fully grasp the power of the old "Placebo-Effect" - which is very alive and well
among even the most well-intentioned listeners. The placebo-effect renders
"audible signatures" easy to detect and describe - if the listener knows which
cable is being heard. But, take away this knowledge during blind or double-blind
listening comparisons and the differences either disappear completely or hover
close to the level of random guessing. Speaking as a competent professional
engineer, designer and manufacturer, nothing would please me and my company's
staff more than being able to design a cable which consistently yielded a
positive score during blind listening comparisons against other cables. But it
only rarely happens - if we wish to be honest!
Oh yes, we have heard of golden-eared audiophiles who claim to be able to
consistently identify "huge, audible differences" between cables. But when these
experts have visited our facility and were put to the test under
carefully-controlled conditions, they invariably failed to yield a score any
better than "chance". For example, when led to believe that three popular cables
were being compared, varying in size from a high-quality 12 AWG ZIP-CORD to a
"high-tech looking" cable with a diameter exceeding an inch, the largest and
sexiest looking cable always scored best - even though the CABLES WERE NEVER
CHANGED and they listened to the ZIP Cord the entire time.
Sorry, but I do not buy the claims of those who say they can always audibly
identify differences between cables, even when the comparisons are properly
controlled to ensure that the identity of the cable being heard is not known by
the listener. We have accomplished too many "true blind comparisons" with
listeners possessing the right credentials, including impeccable hearing
attributes, to know that "real, audible differences" seldom exist - if the
comparisons are properly implemented to eliminate other causes such as system
interactions with cables, etc.
Indeed, during these "comparisons" (without changing cables), some listeners
were able to describe in great detail the "big differences" they thought they
heard in bass, high-end detail, etc. (Of course, the participants were never
told the "NAUGHTY TRUTH", lest they become an enemy for life!)
So why does a reputable company like DAL engage in the design and manufacture of
audiophile loudspeaker cables and interconnects? The answer is simple: Since
significant measurable differences do exist and because well-known and
understood transmission line theory defines optimum relationships between such
parameters as cable impedance and the impedance of the load (loudspeaker), the
capacitance of an interconnect and the input impedance of the following stage,
why not design cables that at least satisfy what theory has to teach? And, since
transmission line theory is universally applied, quite successfully, in the
design of cables intended for TV, microwave, telephone, and other critical
applications requiring peak performance, etc., why not use it in designing
cables intended for critical audiophile applications? Hmmm! To say, as some do,
that there are factors involved that competent engineers and scientists have yet
to identify is utter nonsense and a cover-up for what should be called "pure
snake oil and buzzard salve" - in short, pure "fraud". If any cable
manufacturer, writer, technician, etc. can identify such an audible design
parameter that cannot be measured using available lab equipment or be described
by known theory, I can guarantee a nomination for a "Nobel Prize".
Anyway, I just had to share some of my favorite Hmmm's, regarding cable myths
and seemingly fraudulent claims, with audiophiles on the net who may lack the
technical expertise to separate fact from fiction with regard to cable
performance. I also welcome comments from those who may have other opinions or
who may know of something I might have missed or misunderstood regarding cable
design, theory or secret criteria used by competitors to achieve performance
that cannot be measured or identified by conventional means. Lets all try to get
to the bottom of this mess by open, informed and objective inquiry.
I sincerely believe the time has come for concerned audiophiles, true engineers,
competent physicists, academics, mag editors, etc. to take a firm stand
regarding much of this disturbing new trend in the blatantly false claims
frequently found in cable advertising. If we fail to do so, reputable designers,
engineers, manufacturers, magazine editors and product reviewers may find their
reputation tarnished beyond repair among those of the audiophile community we
are supposed to serve.
Best Regards, John Dunlavy
"Cable Nonsense" Part 2 by John Dunlavy:
The many well-written responses to my recent "cable postings" have
convinced me that a significant number of readers have awakened to the
mess that exists with respect to questionable advertising claims being
made for the properties and performance of audiophile cables.
It has become increasingly obvious that many audiophiles are well
aware that most cable advertising is based upon gibberish intended to
sell expensive, "high-tech looking" cables that seldom perform as
claimed. Indeed, it is a provable fact that most cables, regardless of
cost or appearance, are not designed according to the teachings of
credible engineering criteria, confirmed by meaningful measurements
and properly conducted listening evaluations.
Intrigued by the questionable technology underpinning the advertised
claims for patented cable designs, I contacted a friend who is both a
patent attorney and a competent E.E. As a result of our discussion,
he secured copies of several patents relevant to some of the most
expensive, well-advertised and best-selling cables presently
available. Perusing these patents, I was shocked by much of what I
read. I was also dismayed that the U.S. Patent Office issued them, in
view of the flooby-dust and gobbledygook explanations given for how
they were supposed to work and perform.
Over the past 33 years, I have participated in numerous listening
comparisons, often in the presence of knowledgeable, well-intentioned
audiophiles claiming the ability to "always hear a difference between
cables". These listening sessions frequently took place within
listening rooms that most audiophiles would probably "kill for"!
Initially, before appropriate controls were introduced, results always
favored the most expensive cable with a high-tech appearance and the
greatest "sex appeal"!
However, when "blind", but non-intimidating, controls were instituted,
the differences originally identified could no longer be recognized -
and tabulated results revealed scores very close to those expected for
random-guessing. Yet, many self-proclaimed golden-ear audiophiles
continue to insist that they can always identify audible differences
between cables and abhor "blind evaluations" on the basis of perceived
intimidation.
Reliable studies have conclusively proven that "audible differences"
perceived during poorly-controlled subjective listening comparisons
almost invariably vanish when proper "listening controls" are
instituted. Without proper "blind" controls, listening evaluations
almost never yield any relevant or reliable information regarding
possible differences between cables. (However, such controls must be
designed to effectively eliminate "listener stress" - claimed by some
who do not believe in the relevance of blind comparisons.)
In attempting to eliminate (or reduce) the effect of such perceived
intimidation, we have devised an interesting "deception technique",
wherein we pretend to change cables, letting listeners believe they
know which cable they are hearing, when in reality they are hearing
the same cable throughout the entire session. Interestingly, all
participating listeners invariably continue to identify differences
they believe exist, even though they have listened to the same cable
throughout the evaluation.
An alternate version consists of actually changing cables but mixing
up the order, permitting listeners to believe they are listening to a
particular cable they have earlier identified as possessing certain
audible differences - when they are actually listening to a different
cable. Again, their choice of descriptive adjectives always tracks
the identity of the cable they thought they were listening to, but
were not!
Of course, as I have reiterated many times, it is indeed possible to
sometimes identify barely perceptible differences between
cables. These are almost always traceable to cable/equipment interface
problems, etc., and have always proven to be measurable, quantifiable
and explainable, using well-understood theory and technical knowledge,
along with adequate measurement tools.
Lets now consider the relevance of the many impressive-looking,
high-tech appearing specs and graphs that regularly appear in
expensive magazine advertisements, used to compare presumably
important "measurable" differences between cables. These include
graphs supposedly comparing a zip-cord and one being promoted on the
basis of its superior curve of Joules versus frequency. But a Joule is
defined as a unit of energy or work in the MKS system. In electrical
terms, a Joule is simply a "watt-second". With respect to energy, it
is the work done when "a force of one Newton produces a displacement
of one meter in the direction of the force". However, neither
definition seems very relevant for describing an audible or measurable
property of an audiophile cable.
A similarly impressive-looking graph, advertised as comparing the
"efficiency" of different cables, also begs examination. Here, the
advertisement defined efficiency as being related to "the phase
between voltages and currents along the cable". In the graph,
zip-cord is depicted as exhibiting an efficiency very close to zero at
frequencies below 100 Hertz, including the mains frequency of 60
Hz. But if zip-cord exhibited such a low "efficiency" (according to
normal use of the term), it certainly would not be usable for
supplying A.C. current from an outlet to lights, toasters, fans,
etc. (Indeed, in most household applications, zip-cord would likely
overheat and probably catch fire!) Hmmm!
A further, frequently encountered advertising claim for cables is the
use of "six nines" or 99.9999 percent pure copper (usually designated
6N copper). Such ads usually imply that 6N copper is unique and is
used only in the world's finest and most expensive audio
cables. Further references are often made to an audible correlation
between the use of 6N copper and sonic purity. But, according to the
Directors of the Engineering Departments of several of the largest
wire and cable manufacturers in the United States, virtually all of
today's copper wire is made of "six nines" copper. Every one of them
claimed it would be hard to find any cable, whether zip-cord, house
wiring, etc., that did not use it.
Some cable manufacturers even refer to their products as being made of
special "grain-oriented" copper or copper with "directional
properties", with respect to current/signal flow (gulp)! All large,
reputable wire and cable manufactures, with whom we have spoken, laugh
(or cry) at such assertions and claims. Indeed, if a wire exhibited
directional properties with respect to current flow, the
directionality would "rectify" audio signals (like a diode in series
with a wire carrying an A.C. current), creating unlistenable levels of
second-order harmonic distortion components (wow!).
Another means for selling more loudspeaker cables is that referred to
as "bi-wiring", requiring the use of two cables. However, bi-wiring
does not work in the simplistic fashion imagined by audiophiles
lacking the engineering credentials to analyze the potential system
degradation in accuracy that can result from using separate cables to
connect the output of the power-amp to the separate high and
low-frequency input connectors at the loudspeaker. In fact, such usage
can induce many expensive high-slew rate amplifiers to oscillate at
frequencies above the limit of audibility. This condition can arise
because of the added (effectively doubled) capacitance introduced by
the "bass cable" not being "resistively- terminated" above the bass
crossover frequency and the "mid-tweeter" cable not being
resistively-terminated above the tweeter range, where a typical
tweeter's impedance nearly doubles within each octave above the audio
range.
As well, the issue of bi-amping should be addressed with regards to
using this application in an attempt to better the quality of sonic
reproduction. A straight-forward analysis reveals that this process
may actually adversly affect sound reproduction. This is especially
true when the amps have different properties, such as a tube-amp for
the treble and a solid-state amp for the bass, each possessing
different gains, output impedances, etc. Amplifiers with different
gains, unless compensated to be equal, can audibly affect the
frequency-response, etc. of the loudspeaker.
I could go on and on, ad nauseum, reciting more nonsense, but it seems
prudent to preserve readers from further pain and anguish!
To see what a sampling of competent engineers had to say about typical
cable advertisements, I had three E.E. types (all holding Ph.D's from
different major U.S. universities) read several examples and provide
me with their opinions. Their comments and explanations matched my
own, with all three being in full agreement with the comments I
expressed above. Some of their comments incorporated expletives I
prefer to not to repeat!
Many readers may question my motives for making the above comments and
observations. Well, I originally undertook the task of studying the
properties and design criteria for audio cables for three reasons: (1)
I am the curious type that cannot rest until I have studied the
relevant facts concerning controversial subjects, (2) Measurements of
the electrical properties of a large sampling of commercially
available cables revealed relatively poor performance properties, that
did not correlate with their cost, advertised attributes and or
high-tech appearance, (3) I needed loudspeaker cables and
interconnects with performance as close to "perfect" as possible, so
that I could rule out any contributions from the loudspeaker cables
and interconnects when making measurements of our loudspeakers or
performing critical evaluations with them within our listening room.
But other reasons cut deeper: when advertised performance claims for
products are structured to convey integrity and a sense of being true
in every respect, yet in reality are either misleading or outright
false, the basic covenant of trust that should exist between
manufacturers and consumers is breached. If permitted to continue
unabated and without appropriate redress, increasing consumer distrust
will eventually destroy the integrity of the audiophile industry as a
whole. Ultimately, I believe this has the potential to erode the
rewards available from a very neat hobby, especially for those in
pursuit of "true, documentable perfection" in the reproduction of
music.
When profits and desired market share are given priority by any
manufacturer over their obligation to provide products with
performance and features that conform to advertised claims, I believe
that consumers have a right to know and be concerned. Too many
innocent and uninformed consumers wrongly assume that Government
"protection agencies" are vigilantly pursuing false/misleading
advertising claims and products that do not perform as claimed. Not
so! Today, most government regulatory agencies effectively have their
hands tied behind their backs by bureaucrats representing "special
interest groups" whose only gauge of success is profit - and profit,
alone! As such, they are frequently impotent to take any meaningful
action against companies engaged in advertising, marketing and selling
products whose performance does not meet the rightful expectations of
the purchaser.
Best of listening,
John Dunlavy
P.S. - If anyone would like to introduce credible information or
measurements that disprove any of the comments I have made above, I
would sincerely be open to receiving them.
The many well-written responses to my recent "cable postings" have
convinced me that a significant number of readers have awakened to the
mess that exists with respect to questionable advertising claims being
made for the properties and performance of audiophile cables.
It has become increasingly obvious that many audiophiles are well
aware that most cable advertising is based upon gibberish intended to
sell expensive, "high-tech looking" cables that seldom perform as
claimed. Indeed, it is a provable fact that most cables, regardless of
cost or appearance, are not designed according to the teachings of
credible engineering criteria, confirmed by meaningful measurements
and properly conducted listening evaluations.
Intrigued by the questionable technology underpinning the advertised
claims for patented cable designs, I contacted a friend who is both a
patent attorney and a competent E.E. As a result of our discussion,
he secured copies of several patents relevant to some of the most
expensive, well-advertised and best-selling cables presently
available. Perusing these patents, I was shocked by much of what I
read. I was also dismayed that the U.S. Patent Office issued them, in
view of the flooby-dust and gobbledygook explanations given for how
they were supposed to work and perform.
Over the past 33 years, I have participated in numerous listening
comparisons, often in the presence of knowledgeable, well-intentioned
audiophiles claiming the ability to "always hear a difference between
cables". These listening sessions frequently took place within
listening rooms that most audiophiles would probably "kill for"!
Initially, before appropriate controls were introduced, results always
favored the most expensive cable with a high-tech appearance and the
greatest "sex appeal"!
However, when "blind", but non-intimidating, controls were instituted,
the differences originally identified could no longer be recognized -
and tabulated results revealed scores very close to those expected for
random-guessing. Yet, many self-proclaimed golden-ear audiophiles
continue to insist that they can always identify audible differences
between cables and abhor "blind evaluations" on the basis of perceived
intimidation.
Reliable studies have conclusively proven that "audible differences"
perceived during poorly-controlled subjective listening comparisons
almost invariably vanish when proper "listening controls" are
instituted. Without proper "blind" controls, listening evaluations
almost never yield any relevant or reliable information regarding
possible differences between cables. (However, such controls must be
designed to effectively eliminate "listener stress" - claimed by some
who do not believe in the relevance of blind comparisons.)
In attempting to eliminate (or reduce) the effect of such perceived
intimidation, we have devised an interesting "deception technique",
wherein we pretend to change cables, letting listeners believe they
know which cable they are hearing, when in reality they are hearing
the same cable throughout the entire session. Interestingly, all
participating listeners invariably continue to identify differences
they believe exist, even though they have listened to the same cable
throughout the evaluation.
An alternate version consists of actually changing cables but mixing
up the order, permitting listeners to believe they are listening to a
particular cable they have earlier identified as possessing certain
audible differences - when they are actually listening to a different
cable. Again, their choice of descriptive adjectives always tracks
the identity of the cable they thought they were listening to, but
were not!
Of course, as I have reiterated many times, it is indeed possible to
sometimes identify barely perceptible differences between
cables. These are almost always traceable to cable/equipment interface
problems, etc., and have always proven to be measurable, quantifiable
and explainable, using well-understood theory and technical knowledge,
along with adequate measurement tools.
Lets now consider the relevance of the many impressive-looking,
high-tech appearing specs and graphs that regularly appear in
expensive magazine advertisements, used to compare presumably
important "measurable" differences between cables. These include
graphs supposedly comparing a zip-cord and one being promoted on the
basis of its superior curve of Joules versus frequency. But a Joule is
defined as a unit of energy or work in the MKS system. In electrical
terms, a Joule is simply a "watt-second". With respect to energy, it
is the work done when "a force of one Newton produces a displacement
of one meter in the direction of the force". However, neither
definition seems very relevant for describing an audible or measurable
property of an audiophile cable.
A similarly impressive-looking graph, advertised as comparing the
"efficiency" of different cables, also begs examination. Here, the
advertisement defined efficiency as being related to "the phase
between voltages and currents along the cable". In the graph,
zip-cord is depicted as exhibiting an efficiency very close to zero at
frequencies below 100 Hertz, including the mains frequency of 60
Hz. But if zip-cord exhibited such a low "efficiency" (according to
normal use of the term), it certainly would not be usable for
supplying A.C. current from an outlet to lights, toasters, fans,
etc. (Indeed, in most household applications, zip-cord would likely
overheat and probably catch fire!) Hmmm!
A further, frequently encountered advertising claim for cables is the
use of "six nines" or 99.9999 percent pure copper (usually designated
6N copper). Such ads usually imply that 6N copper is unique and is
used only in the world's finest and most expensive audio
cables. Further references are often made to an audible correlation
between the use of 6N copper and sonic purity. But, according to the
Directors of the Engineering Departments of several of the largest
wire and cable manufacturers in the United States, virtually all of
today's copper wire is made of "six nines" copper. Every one of them
claimed it would be hard to find any cable, whether zip-cord, house
wiring, etc., that did not use it.
Some cable manufacturers even refer to their products as being made of
special "grain-oriented" copper or copper with "directional
properties", with respect to current/signal flow (gulp)! All large,
reputable wire and cable manufactures, with whom we have spoken, laugh
(or cry) at such assertions and claims. Indeed, if a wire exhibited
directional properties with respect to current flow, the
directionality would "rectify" audio signals (like a diode in series
with a wire carrying an A.C. current), creating unlistenable levels of
second-order harmonic distortion components (wow!).
Another means for selling more loudspeaker cables is that referred to
as "bi-wiring", requiring the use of two cables. However, bi-wiring
does not work in the simplistic fashion imagined by audiophiles
lacking the engineering credentials to analyze the potential system
degradation in accuracy that can result from using separate cables to
connect the output of the power-amp to the separate high and
low-frequency input connectors at the loudspeaker. In fact, such usage
can induce many expensive high-slew rate amplifiers to oscillate at
frequencies above the limit of audibility. This condition can arise
because of the added (effectively doubled) capacitance introduced by
the "bass cable" not being "resistively- terminated" above the bass
crossover frequency and the "mid-tweeter" cable not being
resistively-terminated above the tweeter range, where a typical
tweeter's impedance nearly doubles within each octave above the audio
range.
As well, the issue of bi-amping should be addressed with regards to
using this application in an attempt to better the quality of sonic
reproduction. A straight-forward analysis reveals that this process
may actually adversly affect sound reproduction. This is especially
true when the amps have different properties, such as a tube-amp for
the treble and a solid-state amp for the bass, each possessing
different gains, output impedances, etc. Amplifiers with different
gains, unless compensated to be equal, can audibly affect the
frequency-response, etc. of the loudspeaker.
I could go on and on, ad nauseum, reciting more nonsense, but it seems
prudent to preserve readers from further pain and anguish!
To see what a sampling of competent engineers had to say about typical
cable advertisements, I had three E.E. types (all holding Ph.D's from
different major U.S. universities) read several examples and provide
me with their opinions. Their comments and explanations matched my
own, with all three being in full agreement with the comments I
expressed above. Some of their comments incorporated expletives I
prefer to not to repeat!
Many readers may question my motives for making the above comments and
observations. Well, I originally undertook the task of studying the
properties and design criteria for audio cables for three reasons: (1)
I am the curious type that cannot rest until I have studied the
relevant facts concerning controversial subjects, (2) Measurements of
the electrical properties of a large sampling of commercially
available cables revealed relatively poor performance properties, that
did not correlate with their cost, advertised attributes and or
high-tech appearance, (3) I needed loudspeaker cables and
interconnects with performance as close to "perfect" as possible, so
that I could rule out any contributions from the loudspeaker cables
and interconnects when making measurements of our loudspeakers or
performing critical evaluations with them within our listening room.
But other reasons cut deeper: when advertised performance claims for
products are structured to convey integrity and a sense of being true
in every respect, yet in reality are either misleading or outright
false, the basic covenant of trust that should exist between
manufacturers and consumers is breached. If permitted to continue
unabated and without appropriate redress, increasing consumer distrust
will eventually destroy the integrity of the audiophile industry as a
whole. Ultimately, I believe this has the potential to erode the
rewards available from a very neat hobby, especially for those in
pursuit of "true, documentable perfection" in the reproduction of
music.
When profits and desired market share are given priority by any
manufacturer over their obligation to provide products with
performance and features that conform to advertised claims, I believe
that consumers have a right to know and be concerned. Too many
innocent and uninformed consumers wrongly assume that Government
"protection agencies" are vigilantly pursuing false/misleading
advertising claims and products that do not perform as claimed. Not
so! Today, most government regulatory agencies effectively have their
hands tied behind their backs by bureaucrats representing "special
interest groups" whose only gauge of success is profit - and profit,
alone! As such, they are frequently impotent to take any meaningful
action against companies engaged in advertising, marketing and selling
products whose performance does not meet the rightful expectations of
the purchaser.
Best of listening,
John Dunlavy
P.S. - If anyone would like to introduce credible information or
measurements that disprove any of the comments I have made above, I
would sincerely be open to receiving them.
"Cable Nonsense" Part 3 by John Dunlavy:
Thanks to all who responded to my original posting concerning
audiophile cables and their audible/measurable properties.
Since some of the responses seemed to convey a discordant position,
perhaps a more detailed exploration of the issues is justified. A good
beginning might be to examine the issues that separate those whose
opinions are based mainly (or entirely) on subjective grounds (perhaps
from poorly controlled listening evaluations) from those who favor an
objective approach based upon correlating relevant measurements with
the findings of "blind", "double-blind" or other types of
properly-controlled listening comparisons.
To begin, I would like to make clear that I do not believe that a set
of cable measurements, taken alone, can consistently and reliably
predict how one cable will sound when compared to another cable,
without considering relevant "system interface parameters". This is
because the interaction between the electrical properties of a cable
and the input/output impedances (and other properties) of typical
audio equipment/components being connected by the cables are an
integral part of the overall performance equation. Thus, a full and
accurate set of measurements is only relevant if interpreted in the
context of such system interactions.
Given such interpretation, measurements can provide an important, if
not indispensable, guide as to the potential performance of a given
cable within a given system. To say otherwise is to acknowledge an
incomplete grasp of present-day measurement technology and the ability
of credible engineering knowledge/expertise to fully define and
accurately assess all of the relevant properties that affect the
performance of cables within an audio system. Despite the
pontificating of some individuals to the contrary, well-known laws of
physics and principles of engineering are fully adequate to meet the
challenge. (A Nobel nomination awaits anyone who discovers and
adequately identifies a property that proves otherwise!) The notion
that "physics lies", expressed in a recent magazine editorial, is
absolute hogwash!
Most "seemingly" unexplainable, yet truly audible differences between
cables, can be explained if critically examined with respect to
equipment interface considerations. For example, a well-designed,
low-loss loudspeaker cable (with a relatively-low
characteristic-impedance of perhaps 6 to 8 Ohms) can cause many
expensive, well-regarded power-amps (with a slew-rate exceeding
stability limits created by an improperly designed inverse-feedback
loop) to oscillate at frequencies well above the audio range. This is
sometimes audible as a low-level, high-frequency "crackling noise"
(usually emitted by the tweeter as it's voice-coil is being
cooked). Such amplifier instabilities may also alter the "sound" of
the amplifier by creating an "edgy" quality on musical transients or
an exaggeration of high-frequency notes, etc.. But the amplifier, in
this case, is at fault - not the loudspeaker cable.
Unfortunately, this is the reason many audiophiles avoid using
high-performance cables. Yet, a simple "Zobel" network (typically a
6.8 Ohm resistor in series with a 4.7 uF capacitor) in parallel with
the loudspeaker end of the cable can almost always cure the
problem. (A multi-turn coil of 20 AWG wire wound around a 6.8 Ohm, 1
watt resistor, connected in series with the amplifier output
terminals, will usually accomplish the same thing!)
However, while low-loss, low-impedance loudspeaker cables are
technically the ideal choice, from a purely academic point-of view,
most loudspeaker cables are quite short with respect to a wavelength
within the audio spectrum, diminishing the effects of "standing-waves"
and "reflections" that would normally be of concern at frequencies
well above the audio spectrum. But low-impedance low-loss loudspeaker
cables, represent the technical and deserve serious consideration
where "ultimate accuracy" is the goal!
With respect to identifying the cause of audible differences between
some interconnect cables, excessive capacitance is usually the
villain. This is true because transistor output stages of pre-amps, CD
players, etc. are frequently "load-sensitive", especially with respect
to excessive capacitance. This is also true of some single-ended tube
types. Thus, an interconnect cable with a relatively high capacitance
(exceeding 20-30 pF per foot) can often cause some equipment to
exhibit non-linear properties at higher frequencies and/or higher
output levels, resulting in audible levels of distortion. But again,
the cable is not always to blame, although no good engineering reasons
exist for not designing an interconnect cable with a suitably low
capacitance, e.g., below 10-15 pF/ft. However, some of the most
expensive interconnect cables, with a high-tech appearance, exhibit
measured capacitance exceeding 75 pF/ft. while some of the least
expensive ones clock-in at only 12-15 pF/ft. (We believed the problem
sufficiently important to justify the development of an interconnect
cable with a capacitance of only about 8-10 pF/ft.)
Thus, I sincerely hope that the above explanations help to explain why
measurements alone may not always fully explain the differences heard
between cables - without taking into consideration the interactions
between cables and the proclivities exhibited by the output stages of
some amplifiers, etc.. However, accurate measurements, properly made
and interpreted, can almost always predict how a given cable will
react within a given system, taking into account all of the
"interface" considerations that must be evaluated. Therefore,
measurements can be an invaluable design tool when properly
interpreted by a competent engineer seeking optimum performance from a
cable or a system.
So what about subjective listening comparisons for evaluating
"audible" differences between cables? Well, I will once again state
my belief that the "placebo effect is alive and well" and that
listening comparisons are virtually useless unless significant
differences exist and/or proper controls are employed! I base this
belief on a considerable number of carefully conducted and critically
analyzed comparisons between different cables over the past 20-plus
years. Initially, I and my staff fully expected to observe audible
differences - which we did, in the absence of proper and sensible
controls. But in virtually every instance, when controls were
instituted, the differences thought to be easily heard and identified,
either totally disappeared or closely approached the level predicted
by "chance". Yes, we have frequently consulted psychologists and
other experts familiar with "audibility testing" in devising
procedures and controls for our comparison evaluations, etc. But the
results we have obtained have always been consistent: we have simply
not been able to identify any audible artifacts that could not be
explained by a critical examination of the equipment, components,
etc., coupled with an analysis of their interactions --- period!
Keep up the questions - we all have a lot to learn!
Best regards,
John Dunlavy
Thanks to all who responded to my original posting concerning
audiophile cables and their audible/measurable properties.
Since some of the responses seemed to convey a discordant position,
perhaps a more detailed exploration of the issues is justified. A good
beginning might be to examine the issues that separate those whose
opinions are based mainly (or entirely) on subjective grounds (perhaps
from poorly controlled listening evaluations) from those who favor an
objective approach based upon correlating relevant measurements with
the findings of "blind", "double-blind" or other types of
properly-controlled listening comparisons.
To begin, I would like to make clear that I do not believe that a set
of cable measurements, taken alone, can consistently and reliably
predict how one cable will sound when compared to another cable,
without considering relevant "system interface parameters". This is
because the interaction between the electrical properties of a cable
and the input/output impedances (and other properties) of typical
audio equipment/components being connected by the cables are an
integral part of the overall performance equation. Thus, a full and
accurate set of measurements is only relevant if interpreted in the
context of such system interactions.
Given such interpretation, measurements can provide an important, if
not indispensable, guide as to the potential performance of a given
cable within a given system. To say otherwise is to acknowledge an
incomplete grasp of present-day measurement technology and the ability
of credible engineering knowledge/expertise to fully define and
accurately assess all of the relevant properties that affect the
performance of cables within an audio system. Despite the
pontificating of some individuals to the contrary, well-known laws of
physics and principles of engineering are fully adequate to meet the
challenge. (A Nobel nomination awaits anyone who discovers and
adequately identifies a property that proves otherwise!) The notion
that "physics lies", expressed in a recent magazine editorial, is
absolute hogwash!
Most "seemingly" unexplainable, yet truly audible differences between
cables, can be explained if critically examined with respect to
equipment interface considerations. For example, a well-designed,
low-loss loudspeaker cable (with a relatively-low
characteristic-impedance of perhaps 6 to 8 Ohms) can cause many
expensive, well-regarded power-amps (with a slew-rate exceeding
stability limits created by an improperly designed inverse-feedback
loop) to oscillate at frequencies well above the audio range. This is
sometimes audible as a low-level, high-frequency "crackling noise"
(usually emitted by the tweeter as it's voice-coil is being
cooked). Such amplifier instabilities may also alter the "sound" of
the amplifier by creating an "edgy" quality on musical transients or
an exaggeration of high-frequency notes, etc.. But the amplifier, in
this case, is at fault - not the loudspeaker cable.
Unfortunately, this is the reason many audiophiles avoid using
high-performance cables. Yet, a simple "Zobel" network (typically a
6.8 Ohm resistor in series with a 4.7 uF capacitor) in parallel with
the loudspeaker end of the cable can almost always cure the
problem. (A multi-turn coil of 20 AWG wire wound around a 6.8 Ohm, 1
watt resistor, connected in series with the amplifier output
terminals, will usually accomplish the same thing!)
However, while low-loss, low-impedance loudspeaker cables are
technically the ideal choice, from a purely academic point-of view,
most loudspeaker cables are quite short with respect to a wavelength
within the audio spectrum, diminishing the effects of "standing-waves"
and "reflections" that would normally be of concern at frequencies
well above the audio spectrum. But low-impedance low-loss loudspeaker
cables, represent the technical and deserve serious consideration
where "ultimate accuracy" is the goal!
With respect to identifying the cause of audible differences between
some interconnect cables, excessive capacitance is usually the
villain. This is true because transistor output stages of pre-amps, CD
players, etc. are frequently "load-sensitive", especially with respect
to excessive capacitance. This is also true of some single-ended tube
types. Thus, an interconnect cable with a relatively high capacitance
(exceeding 20-30 pF per foot) can often cause some equipment to
exhibit non-linear properties at higher frequencies and/or higher
output levels, resulting in audible levels of distortion. But again,
the cable is not always to blame, although no good engineering reasons
exist for not designing an interconnect cable with a suitably low
capacitance, e.g., below 10-15 pF/ft. However, some of the most
expensive interconnect cables, with a high-tech appearance, exhibit
measured capacitance exceeding 75 pF/ft. while some of the least
expensive ones clock-in at only 12-15 pF/ft. (We believed the problem
sufficiently important to justify the development of an interconnect
cable with a capacitance of only about 8-10 pF/ft.)
Thus, I sincerely hope that the above explanations help to explain why
measurements alone may not always fully explain the differences heard
between cables - without taking into consideration the interactions
between cables and the proclivities exhibited by the output stages of
some amplifiers, etc.. However, accurate measurements, properly made
and interpreted, can almost always predict how a given cable will
react within a given system, taking into account all of the
"interface" considerations that must be evaluated. Therefore,
measurements can be an invaluable design tool when properly
interpreted by a competent engineer seeking optimum performance from a
cable or a system.
So what about subjective listening comparisons for evaluating
"audible" differences between cables? Well, I will once again state
my belief that the "placebo effect is alive and well" and that
listening comparisons are virtually useless unless significant
differences exist and/or proper controls are employed! I base this
belief on a considerable number of carefully conducted and critically
analyzed comparisons between different cables over the past 20-plus
years. Initially, I and my staff fully expected to observe audible
differences - which we did, in the absence of proper and sensible
controls. But in virtually every instance, when controls were
instituted, the differences thought to be easily heard and identified,
either totally disappeared or closely approached the level predicted
by "chance". Yes, we have frequently consulted psychologists and
other experts familiar with "audibility testing" in devising
procedures and controls for our comparison evaluations, etc. But the
results we have obtained have always been consistent: we have simply
not been able to identify any audible artifacts that could not be
explained by a critical examination of the equipment, components,
etc., coupled with an analysis of their interactions --- period!
Keep up the questions - we all have a lot to learn!
Best regards,
John Dunlavy
"Cable Nonsense" Part 4 by John Dunlavy:
The large number of recent postings regarding audiophile cables and
loudspeaker design is encouraging. Perhaps, it is indicative of a
newfound level of interest in the way cables work and perform. Several
posts raised questions and or proffered information that deserve
comment. Unfortunately, my cramped work schedule leaves little time
for writing individual replies to everyone. Therefore, I will try and
lump related answers together and attempt to cover as much important
territory as time allows.
For those who asked how impulse response, step response, amplitude
Vs. frequency response and phase Vs. frequency response are related to
one another, lets consider the following. The impulse-response of any
linear analog network, including amps, loudspeakers, cables, etc., is
important because it contains information about virtually all other
measurable and audible performance properties. Beginning with a
measurement of impulse-response, the frequency-response,
phase-response, cumulative-decay-spectra, step-response, energy-time
response, etc., may be rapidly and accurately determined by FFT
analysis, such as that provided by the now well-known, computer-based,
MLSSA measurement system. (We have three MLSSA systems running
full-time for R&D and production QC applications, in addition to
spectrum analyzers, distortion analyzers, vector-impedance analyzers,
complex waveform generators, etc.)
Further, in answer to another question posed on the NET, variations in
phase Vs. frequency within a linear system are the "first derivative"
of variations in amplitude Vs. frequency. And, variations of amplitude
in the "time domain" produce variations of both amplitude and phase in
the "frequency domain". Indeed, virtually all measurable performance
attributes of any linear system, whether it be an amplifier, a
loudspeaker, a cable, etc., are related to each other in relatively
simple ways that are easily treatable by mathematics - an extremely
powerful tool for those who understand and know how to use and apply
it.
Several posts seem intent on taking issue with what I said about
low-loss, low-impedance loudspeaker cables causing some
poorly-designed power-amps (with a slew-rate exceeding stability
limits created by an improperly designed inverse-feedback loop) to
oscillate. One recent post said: "This is the third time you have
ascribed high slew-rate amplifiers to the problem of cable interface.
This is misleading. It's also the third time I have contradicted you
on this point, which is why I'm sending this reply directly via email
this time (as well as to the ng)".
But in my post on the subject, I never directly related "slew-rate" to
oscillation without the caveat: "... created by an improperly designed
inverse-feedback loop". Indeed, the following text (exactly as I
posted it on the NET) is the relevant paragraph that seems to bother
this particular contributor:
"Most "seemingly" unexplainable, yet truly audible differences between
cables, can be explained if critically examined with respect to
equipment interface considerations. For example, a well-designed,
low-loss loudspeaker cable (with a relatively-low
characteristic-impedance of perhaps 6 to 8 Ohms) can cause many
expensive, well-regarded power-amps (with a slew-rate exceeding
stability limits created by an improperly designed inverse-feedback
loop) to oscillate at frequencies well above the audio range. This is
sometimes audible as a low-level, high-frequency "crackling noise"
(usually emitted by the tweeter as it's voice-coil is being
cooked). Such amplifier instabilities may also alter the "sound" of
the amplifier by creating an "edgy" quality on musical transients or
an exaggeration of high-frequency notes, etc.. But the amplifier, in
this case, is at fault - not the loudspeaker cable."
From the above, I fail to grasp how this person interpreted my
comments as inferring that I believe amplifier stability is directly
related to slew-rate - alone! Far from it, for some of the best
power-amps I have heard and/or tested exhibited very high slew-rate
performance - obtained by using proper high-frequency transistors in a
"minimalist circuit configuration with relatively little
inverse-feedback". I sincerely hope that the above comments set the
record straight and that I do, indeed, understand network/circuit
theory, transmission-line theory, amp design, slew-rate, stability
margin, inverse-feedback problems, etc.
One post on rahe recently noted that, "I've been following
Stereophile's analysis of time-coherence for a while now, and have
noticed that almost none of the speakers reviewed are time-coherent,
including those which received excellent ratings." Without attempting
to justify "excellent ratings" sometimes given by Stereophile for
loudspeakers that do not exhibit "time-coherent" performance (good
impulse, step, waterfall and energy-time responses), their reviews are
most often an amalgam of two different approaches for judging
"accuracy": 1) subjectively perceived accuracy (based upon listening)
and, 2) objective accuracy (determined by assessing a full-set of
accurate measurements). The best reviews, in my opinion, are those
that compare the results of both and attempt to resolve and explain
any lack of correlation that might exist. Subjectively determined
accuracy, taken alone, is an unreliable means for establishing the
acoustical merits of audiophile components. This is because even the
most honest attempt at determining accuracy by listening, is subject
to personal experience, preferences, whims, long and short-term
memory, program material, equipment interface problems, listening room
modes, etc. Also, one reviewer might consider a "warm, mellow sound"
to be most accurate while another might be attracted by a "more
detailed, analytical sound" and so forth. If a multi-member group
listens to a system and attempts to arrive at a consensus regarding
its accuracy relative to some "standard", the danger exists that the
strongest-willed member may, without consciously intending to do so,
inadvertently impose his or her choice on the other listeners.
Several individuals have inquired as to why we designed and sell our
own loudspeaker cables and interconnects. The answer is simple: we
believe that most audiophile cables are very over-priced, do not
perform as advertised and do not provide the technical properties
required to insure the best possible system performance (taking into
consideration system interface problems). For example, most
interconnect cables exhibit a sufficiently high capacitance (typically
in excess of 30 pF/ft.) to cause non-linear distortion at
high-frequencies when used with some pre-amps and power-amps. The
relatively inexpensive top-of-the-line Radio Shack interconnects are a
shinning example of an excellent performing, low-capacitance cable
(typically about 15 pF/ft.) that is very, very affordable. Our own
interconnect cable exhibits nearly half the capacitance but is a bit
more expensive - though very affordable for most audiophiles.
With respect to loudspeaker cables, we measured most of the best known
and most expensive audiophile brands and were shocked to find that
little correlation existed between selling price and measured/audible
performance. If you read back to some of my earlier postings on the
subject, you will discover that I covered the matter in a reasonably
thorough manner. We will continue to design and market our own cables
to meet a consumer and professional demand for cables offering
credible performance, based upon solid engineering criteria and
accurate measurements of all relevant performance parameters - at very
affordable prices. While we do so, we also tell audiophiles and
professional users that, especially for relatively short lengths of
cable, there appears to be no consistently audible difference between
most loudspeaker cables (including high-quality #20 AWG Zip-cord). The
same applies to most interconnect cables, regardless of their cost.
But, in my opinion, it costs no more to design and manufacture cables
that conform to the dictates of good engineering practice than those
cables whose properties and performance are very questionable. So, why
not do so - and give customers a break from all the flooby-dust,
buzzard-salve, snake-oil and hokum that surrounds the advertising of
too many of today's cables?
Best Regards,
John Dunlavy
The large number of recent postings regarding audiophile cables and
loudspeaker design is encouraging. Perhaps, it is indicative of a
newfound level of interest in the way cables work and perform. Several
posts raised questions and or proffered information that deserve
comment. Unfortunately, my cramped work schedule leaves little time
for writing individual replies to everyone. Therefore, I will try and
lump related answers together and attempt to cover as much important
territory as time allows.
For those who asked how impulse response, step response, amplitude
Vs. frequency response and phase Vs. frequency response are related to
one another, lets consider the following. The impulse-response of any
linear analog network, including amps, loudspeakers, cables, etc., is
important because it contains information about virtually all other
measurable and audible performance properties. Beginning with a
measurement of impulse-response, the frequency-response,
phase-response, cumulative-decay-spectra, step-response, energy-time
response, etc., may be rapidly and accurately determined by FFT
analysis, such as that provided by the now well-known, computer-based,
MLSSA measurement system. (We have three MLSSA systems running
full-time for R&D and production QC applications, in addition to
spectrum analyzers, distortion analyzers, vector-impedance analyzers,
complex waveform generators, etc.)
Further, in answer to another question posed on the NET, variations in
phase Vs. frequency within a linear system are the "first derivative"
of variations in amplitude Vs. frequency. And, variations of amplitude
in the "time domain" produce variations of both amplitude and phase in
the "frequency domain". Indeed, virtually all measurable performance
attributes of any linear system, whether it be an amplifier, a
loudspeaker, a cable, etc., are related to each other in relatively
simple ways that are easily treatable by mathematics - an extremely
powerful tool for those who understand and know how to use and apply
it.
Several posts seem intent on taking issue with what I said about
low-loss, low-impedance loudspeaker cables causing some
poorly-designed power-amps (with a slew-rate exceeding stability
limits created by an improperly designed inverse-feedback loop) to
oscillate. One recent post said: "This is the third time you have
ascribed high slew-rate amplifiers to the problem of cable interface.
This is misleading. It's also the third time I have contradicted you
on this point, which is why I'm sending this reply directly via email
this time (as well as to the ng)".
But in my post on the subject, I never directly related "slew-rate" to
oscillation without the caveat: "... created by an improperly designed
inverse-feedback loop". Indeed, the following text (exactly as I
posted it on the NET) is the relevant paragraph that seems to bother
this particular contributor:
"Most "seemingly" unexplainable, yet truly audible differences between
cables, can be explained if critically examined with respect to
equipment interface considerations. For example, a well-designed,
low-loss loudspeaker cable (with a relatively-low
characteristic-impedance of perhaps 6 to 8 Ohms) can cause many
expensive, well-regarded power-amps (with a slew-rate exceeding
stability limits created by an improperly designed inverse-feedback
loop) to oscillate at frequencies well above the audio range. This is
sometimes audible as a low-level, high-frequency "crackling noise"
(usually emitted by the tweeter as it's voice-coil is being
cooked). Such amplifier instabilities may also alter the "sound" of
the amplifier by creating an "edgy" quality on musical transients or
an exaggeration of high-frequency notes, etc.. But the amplifier, in
this case, is at fault - not the loudspeaker cable."
From the above, I fail to grasp how this person interpreted my
comments as inferring that I believe amplifier stability is directly
related to slew-rate - alone! Far from it, for some of the best
power-amps I have heard and/or tested exhibited very high slew-rate
performance - obtained by using proper high-frequency transistors in a
"minimalist circuit configuration with relatively little
inverse-feedback". I sincerely hope that the above comments set the
record straight and that I do, indeed, understand network/circuit
theory, transmission-line theory, amp design, slew-rate, stability
margin, inverse-feedback problems, etc.
One post on rahe recently noted that, "I've been following
Stereophile's analysis of time-coherence for a while now, and have
noticed that almost none of the speakers reviewed are time-coherent,
including those which received excellent ratings." Without attempting
to justify "excellent ratings" sometimes given by Stereophile for
loudspeakers that do not exhibit "time-coherent" performance (good
impulse, step, waterfall and energy-time responses), their reviews are
most often an amalgam of two different approaches for judging
"accuracy": 1) subjectively perceived accuracy (based upon listening)
and, 2) objective accuracy (determined by assessing a full-set of
accurate measurements). The best reviews, in my opinion, are those
that compare the results of both and attempt to resolve and explain
any lack of correlation that might exist. Subjectively determined
accuracy, taken alone, is an unreliable means for establishing the
acoustical merits of audiophile components. This is because even the
most honest attempt at determining accuracy by listening, is subject
to personal experience, preferences, whims, long and short-term
memory, program material, equipment interface problems, listening room
modes, etc. Also, one reviewer might consider a "warm, mellow sound"
to be most accurate while another might be attracted by a "more
detailed, analytical sound" and so forth. If a multi-member group
listens to a system and attempts to arrive at a consensus regarding
its accuracy relative to some "standard", the danger exists that the
strongest-willed member may, without consciously intending to do so,
inadvertently impose his or her choice on the other listeners.
Several individuals have inquired as to why we designed and sell our
own loudspeaker cables and interconnects. The answer is simple: we
believe that most audiophile cables are very over-priced, do not
perform as advertised and do not provide the technical properties
required to insure the best possible system performance (taking into
consideration system interface problems). For example, most
interconnect cables exhibit a sufficiently high capacitance (typically
in excess of 30 pF/ft.) to cause non-linear distortion at
high-frequencies when used with some pre-amps and power-amps. The
relatively inexpensive top-of-the-line Radio Shack interconnects are a
shinning example of an excellent performing, low-capacitance cable
(typically about 15 pF/ft.) that is very, very affordable. Our own
interconnect cable exhibits nearly half the capacitance but is a bit
more expensive - though very affordable for most audiophiles.
With respect to loudspeaker cables, we measured most of the best known
and most expensive audiophile brands and were shocked to find that
little correlation existed between selling price and measured/audible
performance. If you read back to some of my earlier postings on the
subject, you will discover that I covered the matter in a reasonably
thorough manner. We will continue to design and market our own cables
to meet a consumer and professional demand for cables offering
credible performance, based upon solid engineering criteria and
accurate measurements of all relevant performance parameters - at very
affordable prices. While we do so, we also tell audiophiles and
professional users that, especially for relatively short lengths of
cable, there appears to be no consistently audible difference between
most loudspeaker cables (including high-quality #20 AWG Zip-cord). The
same applies to most interconnect cables, regardless of their cost.
But, in my opinion, it costs no more to design and manufacture cables
that conform to the dictates of good engineering practice than those
cables whose properties and performance are very questionable. So, why
not do so - and give customers a break from all the flooby-dust,
buzzard-salve, snake-oil and hokum that surrounds the advertising of
too many of today's cables?
Best Regards,
John Dunlavy
Many years ago I created for Monster Cable a line of cables known as M-Series M2.2 and M2.4 (bi-wire version). The specific feature never formally called, out but definitely can make a difference (see above), was a 25 Watt Caddock film resistor across the speaker end buried in a housing filled with thermally conductive epoxy. It was an effort to make a real difference in a cable in a market full of some amazing claims. Lots were sold thanks to the sales team and the large market for audio products at the time.
It would seem that if we had waited there would be more technical validation of the concept. However by the mid-2000's the market for receivers and speakers had dried up.
It would seem that if we had waited there would be more technical validation of the concept. However by the mid-2000's the market for receivers and speakers had dried up.
Is this a rip-off? Already?
https://www.amazon.com/Designing-Au...rds=bob+cordell&qid=1575019616&s=books&sr=1-2
Jan
https://www.amazon.com/Designing-Au...rds=bob+cordell&qid=1575019616&s=books&sr=1-2
Jan