The problem of assessing any driver with the limited criteria we use is really still only a rough selection process. Listening tests really are the
quickest way - common sense- and you and Lynn have done this, and I trust this more than any limited tests. If it sounds good with a number of people that defines it, through different amps, material etc.
However, if we could fully assess to give complete spectral and sound pressure level test using pulse testing at different power levels, along with water fall tests we would get a long way, but which do you do first. I would say listen and then test. A Deltalite unit may prove a better sound on audition, and maybe on lab testing than the JB2226 or 416, but I would feel comfortable with buying the 416 before considering any other woofer from the comments on the forum.
Both drivers were in the piston band; the response, as expected, was completely flat, aside from very small glitches from the spider around 500 Hz (pretty much all bass drivers have very small response glitches from the spider).
If the drivers didn't have piston-band responses, I'd reject them out of hand as defective, and not even bother to listen to them.
The measured variations I've seen in the (musically very important) 100~500 Hz region all come down to misbehavior from the enclosure. Reflections from the back wall, internal standing waves, and unwanted (and very high-Q) emissions from the cabinet walls are all troublesome and not easy to remove. Much of the attraction of the OB systems comes down to absence of cabinet colorations.
Some people are more sensitive to cabinet colorations than others. A great way to sensitize yourself to these colorations is placing your ear directly on the side of the cabinet while music is playing quietly; another method is listening to the hollow sounds you hear when the driver is removed and you place your head close to, or directly in, the cabinet opening. These characteristic hollow sounds will then be noticeable when you're listening in the usual listening position.
I don't recommend this subjective exercise to anyone unless you're pretty serious about loudspeaker design. Like training yourself to see LCD or plasma-TV flicker, you can't unlearn it, and you'll start becoming aware of it all the time. This subjective training is a great way to become a OB enthusiast, since building a quiet enclosure, particularly a big one, is not a trivial project.
The comparison that I did was comparing two drivers in the piston-band with the same enclosure. Driver response is flat, enclosure is the same, crossover is 3rd-order lowpass at 700 Hz. The crud at 1500 Hz and higher is being pretty efficiently filtered. I compared the GPA 416-Alnico to the JBL 2226, which is a highly-respected modern driver used widely in professional applications. Gary Dahl compared the GPA 416-Alnico to the Acoustic Elegance TD-15M (which he already owned). These were separate tests done in separate parts of the country by different people with different musical tastes.
We both preferred the GPA 416-Alnico to the other drivers, even though we'd already paid for the other drivers with our own money, and had a financial incentive to keep what we had. We didn't want the GPA to sound better, or even different. Both of us wanted to stick with what we already had. But that's not how it turned out.
It's true some problems can be equalized out; but others can't. In this case, there's nothing to equalize, since the measured response of all the drivers in the working range is flat. So the subjective differences between the 15" bass drivers must have a different cause.
The hypothesized mechanisms are cone coloration, adhesive coloration, stiction in the spider assembly, small-signal magnetic nonlinearities (overhung vs underhung voice coils), flux modulation of the magnet, and for all I know, the astrological rising sign on the day the driver design was completed.
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Lynn, did you measure both drivers to make sure their response was actually identical ?
Piston range is about the behavior of the cone itself, and does not say anything about the response shape. A stronger motor (and/or lighter cone) will give a rising response (ie higher mass breakpoint frequency) already above 200Hz.
About the filter, a 3rd order LP is not enough if the driver were listen to without a compression driver above: the HF response differences will still be heard and influence the perception (that has been my experience when evaluating 12" midbass drivers, and I had to use brickwall filters)
Piston range is about the behavior of the cone itself, and does not say anything about the response shape. A stronger motor (and/or lighter cone) will give a rising response (ie higher mass breakpoint frequency) already above 200Hz.
About the filter, a 3rd order LP is not enough if the driver were listen to without a compression driver above: the HF response differences will still be heard and influence the perception (that has been my experience when evaluating 12" midbass drivers, and I had to use brickwall filters)
You have made some useful and helpful comments, which also relate to my response to Gary. Again, I believe an actual impulse response at a range of power levels regimen on the actual drivers is the criterion after auditioning in some simple set without any cross over, and decent impedance matching with the source amplifier.
Listening comes before testing, and is quick to carry out. For example you prefer Alnico magnets for 416 but can you measure a difference in the lab. I bet not.
Boldname,
I would concur that if two magnets, Neo and Alnico with the same absolute flux density should be very hard to measure or hear a difference. What is almost always true is that with the Neo magnet motor the steel structure will be very different as you do not have to fit the much larger slug of magnetic material that is required to use the Alnico and therefor they really aren't comparable motors. If you made the structures more similar you would see most of the differences disappear. Now a ceramic magnet does have higher distortion numbers, just a consequence of the magnetic material and increases in internal eddy currents and higher reluctance of that material.
I would concur that if two magnets, Neo and Alnico with the same absolute flux density should be very hard to measure or hear a difference. What is almost always true is that with the Neo magnet motor the steel structure will be very different as you do not have to fit the much larger slug of magnetic material that is required to use the Alnico and therefor they really aren't comparable motors. If you made the structures more similar you would see most of the differences disappear. Now a ceramic magnet does have higher distortion numbers, just a consequence of the magnetic material and increases in internal eddy currents and higher reluctance of that material.
Nearfield response of the GPA 416-Alnico and the JBL 2226 in the 100~700 Hz region wasn't very interesting. They looked pretty much interchangeable, like good-quality 15" drivers. Both drivers are also pretty well-behaved in the 1~2 kHz region, with the typical broad peak centered around 1.5 kHz. The smooth behavior in this region suggests they were designed for 2-way studio monitor applications.
The subjective difference between the two drivers did not sound like a frequency-balance difference; it was more like a change of power amplifiers or DACs. This metaphor isn't helpful if your experience is that all power amps and DACs sound the same, but that's what it sounded like to me.
This is why I'm curious about small-signal behavior (-40 to -90 dB down from peak levels), which is one of areas where amplifiers and DACs are different from each other. The magnetic systems of the two drivers are quite different from each other, and also different from the majority of medium-to-low efficiency audiophile-oriented drivers.
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I share the same interest about small signal behavior (especially dynamic), and it looks like good acoustical impedance adaptation (large drivers or horns with a low flare rate) bring something there. It might well be that mechanical resistance is also part of the mix...
Nonetheless, other differences must first be cleared out before concluding anything.
Did you had a driver covering the >700Hz range when doing your comparison?
If not, then let me reiterate my claim that a 3rd order LP is not enough to remove the differences in the highs between these drivers (breakup region!) when not masked by another driver. This could definitely give the impression of a more vivid and dynamic driver.
Nonetheless, other differences must first be cleared out before concluding anything.
Did you had a driver covering the >700Hz range when doing your comparison?
If not, then let me reiterate my claim that a 3rd order LP is not enough to remove the differences in the highs between these drivers (breakup region!) when not masked by another driver. This could definitely give the impression of a more vivid and dynamic driver.
Yes, the comparisons were made with the AH425 and the Radian 745Neo/Al in use. The LF crossover was trimmed, and Zobel inductance corrector re-adjusted, to allow for the differences between the two drivers.
I expected small subjective differences, in the range of 0.5 dB or so, but what I heard was a different presentation on the 160 ~ 500 Hz range. The 1 ~ 3 kHz region, as expected, was dominated by the sound of the AH425 and the Radian 745Neo/Al, and positional differences of 0.5" were audible. Fortunately, the best impulse response and the best subjective impression happened to coincide.
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Yes, the construction geometry to achieve as linear a field as possible for the gap and achieve a high flux density has many variables. One wonders always about the absolute audible impacts through the operating band that arise from the differences. What is the real subjective impact at all frequencies, of intermixing and power levels, in the realm of all general reproduction.
I have seen neo motors with copper Faraday rings. Faraday rings etc have of course allowed the ceramic magnets to achieve much better results.
Better surrounds have help the current range of diaphragm fabrcs/materials.
We know there are audiphile speaker designers, that dispute the real sound appeal differences, for properly designed high tech drivers, designed to be the best with the range of magnet materials available today.
It may have been slap a coil in a magnetic gap once. What I ponder is some of these small speakers, fitted to the mass produced product, especially for any one of the vogue modern reproducers that it sets a very high standard that any high dB system will be unable to emulate or match.
It matters, as it is a disappointment, when any big dB behemoth speaker, if beautifully designed and constructed leaves a sense of something missing in the reproduction. This is not aimed at any body, but represents a general paradigm and applies to the whole realm of speaker availabilty.
Yes, I want it capable of going loud but it has to be bl...... good. The Thiele parameters etc are vital in this process, but in the end it needs a Zaph or Ralph or even ourselves to get beyond the review of technical performance or measurement to a winning practical driver. Even the SEAS 27TBFCG springs to mind as one of a few drivers, and well known B & C may be another with its polyester diaphragm. And these are not for big bucks.
Boldname,
It is the quandary that a speaker designer has to work against of what the final end use of the speaker is intended for and the size of that speaker. If you are attempting to make a two way system and the speaker size is limited you are designing against a different set of criteria than if you are designing a three way system and you can use a large format 15" speaker for the bass. You have to decide what is important in each design you make. If I was doing a 15" I wouldn't necessarily design the same type of magnetic structure as I would while trying to make a small format driver hit let's say the same 35Hz lower frequency response limit. In the larger speaker I could design around a much lower excursion and therefor use a shorter gap motor assembly and have higher flux density giving a higher efficiency. In a small speaker giving a low frequency response I need to either use an overhung voicecoil or I need to use a short coil and long gap to achieve any kind of higher spl level bass output and you just can't compare that to a large 15" speaker that doesn't need much excursion to achieve the same spl output. This is where the tradeoffs become so evident. The problem on the other hand with the large 15" speaker is when someone wants to use that as a two-way system and expects extremely linear frequency response above the pistonic range, you have to deal with cone breakup modes, it is just a given. So any speaker design is a series of compromises in-order to meet specific end uses. One advantage we have today over very early speaker designs is the much greater amplifier output with solid state devices, if you will only limit yourself to vacuum tube amplification you are back to the limitations of output power and then efficiency becomes the driving force in how you will design the speaker. There really are no universal answers to these questions.
It is the quandary that a speaker designer has to work against of what the final end use of the speaker is intended for and the size of that speaker. If you are attempting to make a two way system and the speaker size is limited you are designing against a different set of criteria than if you are designing a three way system and you can use a large format 15" speaker for the bass. You have to decide what is important in each design you make. If I was doing a 15" I wouldn't necessarily design the same type of magnetic structure as I would while trying to make a small format driver hit let's say the same 35Hz lower frequency response limit. In the larger speaker I could design around a much lower excursion and therefor use a shorter gap motor assembly and have higher flux density giving a higher efficiency. In a small speaker giving a low frequency response I need to either use an overhung voicecoil or I need to use a short coil and long gap to achieve any kind of higher spl level bass output and you just can't compare that to a large 15" speaker that doesn't need much excursion to achieve the same spl output. This is where the tradeoffs become so evident. The problem on the other hand with the large 15" speaker is when someone wants to use that as a two-way system and expects extremely linear frequency response above the pistonic range, you have to deal with cone breakup modes, it is just a given. So any speaker design is a series of compromises in-order to meet specific end uses. One advantage we have today over very early speaker designs is the much greater amplifier output with solid state devices, if you will only limit yourself to vacuum tube amplification you are back to the limitations of output power and then efficiency becomes the driving force in how you will design the speaker. There really are no universal answers to these questions.
Pos, Lynn, Gary, anyone ?
EBP ( in Hz ) = Bl^ / ( 2 x Pi x Re x mms )
- Bl^ = Bl*Bl
- mms is stated in Kilograms
The formula nicely demonstrates the relationships between cone weights ( moving mass ) , motor strength & resistance , and how they interact to give what we perceive as the fundamental "voice" of a transducer .
Developing a working knowledge of this formula , can help illuminate the "mystery" of the differences perceived , between seemingly similar woofers .
After-all ( according to this formula ) , the GPA model is "voiced" around 76hz while the JBL is voiced up around 120hz .
One is decidedly voiced within ( what I deem to be ) the bass region , while the other has been pushed up into the mid-bass area .
- These higher voicing ( when found in a 15" speaker ) are typical of modern day woofers meant for SR work .
EBP ( in Hz ) = Bl^ / ( 2 x Pi x Re x mms )
- Bl^ = Bl*Bl
- mms is stated in Kilograms
The formula nicely demonstrates the relationships between cone weights ( moving mass ) , motor strength & resistance , and how they interact to give what we perceive as the fundamental "voice" of a transducer .
Developing a working knowledge of this formula , can help illuminate the "mystery" of the differences perceived , between seemingly similar woofers .
After-all ( according to this formula ) , the GPA model is "voiced" around 76hz while the JBL is voiced up around 120hz .
One is decidedly voiced within ( what I deem to be ) the bass region , while the other has been pushed up into the mid-bass area .
- These higher voicing ( when found in a 15" speaker ) are typical of modern day woofers meant for SR work .
EarlK,
If it was only that simple. What you have to consider is though two speakers can have the same measured moving mass that mass can be in very different places. The weights of the voicecoil, former, cone, surround and spider can all be very different and still add to the same total mass. This may define the efficiency given the same flux density and B/L factor but so many changes can cause a very different sonic signature between device that this is how some simple comparisons just don't work subjectively. One speaker can have a very light weight and thin cone and another a heavy and thick cone and still have the same final moving mass. Those two speakers will not sound the same. This is one of the real problems with only looking at T/S values when picking devices. The lumped sum analysis just doesn't address all of these variables.
If it was only that simple. What you have to consider is though two speakers can have the same measured moving mass that mass can be in very different places. The weights of the voicecoil, former, cone, surround and spider can all be very different and still add to the same total mass. This may define the efficiency given the same flux density and B/L factor but so many changes can cause a very different sonic signature between device that this is how some simple comparisons just don't work subjectively. One speaker can have a very light weight and thin cone and another a heavy and thick cone and still have the same final moving mass. Those two speakers will not sound the same. This is one of the real problems with only looking at T/S values when picking devices. The lumped sum analysis just doesn't address all of these variables.
Hi Earl,
AFAIK EBP is F/Q
Your formula here is the mass breakpoint frequency (or half of it, depending on the definition used).
I agree this will definitely influence the response shape (see post #11786)
AFAIK EBP is F/Q
Your formula here is the mass breakpoint frequency (or half of it, depending on the definition used).
I agree this will definitely influence the response shape (see post #11786)
I agree the formula is really quite primitive as it was stated ( though not quite as obtuse as EBP = Fs/Qes ) .
Still, in this primitive form ( & used soley as a first pass selection tool ) it's able to separate out the possible contenders from the crowded field ( broadly speaking ) .
IME, it's usage would have excluded ( for auditioning purposes ) any 15" registering a number much above 100 hz .
EarlK,
I guess if our first criteria is to look at the Fs of a speaker to determine if it is even in the ballpark for our use that at least it is a start. Unfortunately that is all that it is, a start to throw out those that can never get where we are trying to go. Fs and the type of box or no box design also needs to be part of that initial determination. You wouldn't necessarily use the same driver in a sealed enclosure as you would in a BR enclosure and an OB is an altogether different can of worms.
I guess if our first criteria is to look at the Fs of a speaker to determine if it is even in the ballpark for our use that at least it is a start. Unfortunately that is all that it is, a start to throw out those that can never get where we are trying to go. Fs and the type of box or no box design also needs to be part of that initial determination. You wouldn't necessarily use the same driver in a sealed enclosure as you would in a BR enclosure and an OB is an altogether different can of worms.