The "search" function in your hands will save me much typing, and I am fundamentally lazy.😀 Include the word "crossover" to narrow things down (this happened in an electronic crossover project).
edit: here's the first telling: http://www.diyaudio.com/forums/full-range/121236-favorite-speaker-wire.html#post1484644
edit: here's the first telling: http://www.diyaudio.com/forums/full-range/121236-favorite-speaker-wire.html#post1484644
Just looked at that post - the telling thing was that the cable was 'proper' cable, taken from serious RF equipment - where it obviously hadn't caused a significant issue for the operation of that unit.
Unfortunately the conventional, theoretical reasoning about why these effects should not be audible, as expressed in the last page or so here, doesn't bear out. The effect is audible, I can hear it, if I ignore it the degradation remains until I do something about it. Now, I'm as interested as anyone else as to why it occurs, but I haven't found anything seriously explorative of the behaviour in the literature - it's generally the same repetition, of the same basic concepts, almost boilerplated from one piece to the next.
Trouble is, it's real will o' the wisp behaviour, most people just want it to go away, so the real focus is on just stopping it, rather than precisely analysing how it may impact in some non-obvious manner ...
Unfortunately the conventional, theoretical reasoning about why these effects should not be audible, as expressed in the last page or so here, doesn't bear out. The effect is audible, I can hear it, if I ignore it the degradation remains until I do something about it. Now, I'm as interested as anyone else as to why it occurs, but I haven't found anything seriously explorative of the behaviour in the literature - it's generally the same repetition, of the same basic concepts, almost boilerplated from one piece to the next.
Trouble is, it's real will o' the wisp behaviour, most people just want it to go away, so the real focus is on just stopping it, rather than precisely analysing how it may impact in some non-obvious manner ...
SY, I still have some questions regarding microphonics due to triboelectric
effects in PTFE / silver cables:
From the link you have posted it appears that you observered a microphonic
effect on specifically _one_ make of cable which happend to be PTFE / silver.
How did you verify that this was due to a triboelectric effect ?
Did you test other PTFE / silver cables, so you can conclude all PTFE / silver are that way ?
Bedea (a well reputed manufacturer, not a "boutique" brand) makes some
low noise cables:
Low noise coaxial cables
some of them actually use PTFE and copper braid silver plated shielding:
LN5002 LowNoise coaxial cable - coaxial line: koax24
effects in PTFE / silver cables:
From the link you have posted it appears that you observered a microphonic
effect on specifically _one_ make of cable which happend to be PTFE / silver.
How did you verify that this was due to a triboelectric effect ?
Did you test other PTFE / silver cables, so you can conclude all PTFE / silver are that way ?
Bedea (a well reputed manufacturer, not a "boutique" brand) makes some
low noise cables:
Low noise coaxial cables
some of them actually use PTFE and copper braid silver plated shielding:
LN5002 LowNoise coaxial cable - coaxial line: koax24
I guess it is the 'special layer of tissue' which prevents the PTFE and conductor to make physical contact.
Well might be, but they use an additional layer on their other non PTFE cables too.
What I wonder how the conclusion emerged that this has to be triboelectric effect
of PTFE / silver.
What I wonder how the conclusion emerged that this has to be triboelectric effect
of PTFE / silver.
Did some Google searches meanwhile and there seems to be no general
consensus about this, sometimes even the same person seems to disagree
with himself:
Bruno Putzeys about microphone cables (2004):
Cable Distortion and Dielectric Biasing Debunked | Audioholics
"To make matters worse, teflon and silver are about the worst thinkable combination in terms of triboelecticity."
Bruno Putzeys 4 years later:
A Microphonic Wire?
"I don't agree that PTFE/Silver Plated cable is bad for microphony. ...
Furthermore, PTFE is very stiff so it produces a relatively high mechanical Q. I've tested a lot of cable for microphonics and teflon cables were simply in a leage of their own."
Seems a to be a confusing issue ...
consensus about this, sometimes even the same person seems to disagree
with himself:
Bruno Putzeys about microphone cables (2004):
Cable Distortion and Dielectric Biasing Debunked | Audioholics
"To make matters worse, teflon and silver are about the worst thinkable combination in terms of triboelecticity."
Bruno Putzeys 4 years later:
A Microphonic Wire?
"I don't agree that PTFE/Silver Plated cable is bad for microphony. ...
Furthermore, PTFE is very stiff so it produces a relatively high mechanical Q. I've tested a lot of cable for microphonics and teflon cables were simply in a leage of their own."
Seems a to be a confusing issue ...
I hear any tapping, sliding, vibration... things acted like a perfectly microphonic circuit (which is what I thought it was until belatedly replacing the shielded cable and having the microphonics disappear). If I were a bit of a snake, I would have built this into a cabinet and sold it to some gullible audiophile with a rap about the "bloom" and "liveliness."
No, and I wouldn't claim that. That kind of shielded cable is expensive and unnecessary, so I wasn't going to buy more- it's more effective to avoid it in the first place by using other, cheaper dielectrics and wire materials which are less susceptible to triboelectric effects. Yes, I could spend a pile and get a PTFE/silver cable where pains have been taken to eliminate those effects and get something which performs identically to PVC/tinned copper at only 20 times the price. The advantage to PTFE in audio frequency circuits is temperature range, which isn't really relevant.
"Free" was a big attraction for that particular coax. And it was worth every penny. 😀
Ah, yes I see it now. So I might better avoid PTFE and use rather this:
http://www.koax24.de/en/coaxial-cable/overview-50-o/24-32-mm-gr2/bedea-mxr-04514l-lownoise.html
which is at 1/4 the price 🙂
But what to do with that 20 ft. nice "teflon silver plated military grade cable" I still have ?
http://www.koax24.de/en/coaxial-cable/overview-50-o/24-32-mm-gr2/bedea-mxr-04514l-lownoise.html
which is at 1/4 the price 🙂
But what to do with that 20 ft. nice "teflon silver plated military grade cable" I still have ?
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Georg,
I would still use that nice cable and check if you can replicate SY's findings. If not, you are good to go. I use small dia coax teflon/silver coated because of the ease of soldering in tiny quarters, never had problems as described by others. We shouldn't over-exaggerate this tribo-electric phenomenom.
I would still use that nice cable and check if you can replicate SY's findings. If not, you are good to go. I use small dia coax teflon/silver coated because of the ease of soldering in tiny quarters, never had problems as described by others. We shouldn't over-exaggerate this tribo-electric phenomenom.
Impedances are everything. If the source and/or terminating impedance is low, this is less likely to be a problem. But for cases like mine (running between a volume control pot and a circuit input, it very much can be.
FWIW, I still have some of that coax and am sending it to Pano to play with.
Most likely. I'll be trying it sourced from a 50K log pot (the volume control) to a 220K ohm input and also a 20K ohm input (sound cards). I'll post the results for all to hear.
OK, so there's 25k source impedance in parallel with 220k load impedance, so call it 22k. Accepting Dave's guesstimate (I am somewhat skeptical of it- I think you have to look at charge generated vs discharge time) of 10s of nA, that's 0.2mV. I think that's too low, but I only had a sample of one (times two channels, of course), set up differently, and no time to pursue or quantify it.
This was what I was originally asking anyway: how the answer was attributed to discharge within the cable. Every single thing in the world is vibrating and moving somewhat 100% of the time. You do have to cross a threshold, however, to strip off free charges. You have to once again do this enough times to build up a meaningful potential, and I'm still not convinced that this is possible in any form of audio cable. Unless you're creating an electric field at the ends of a cable rather than along its length, I still don't see how it's possible to attribute microphonics to minute amounts of static buildup.
Charges are created by triboelectricity- that's just plain well-known physics. They will discharge according to basic E&M- again, just plain well-known physics. The discharge is a transient signal, ditto. PTFE and silver are a combination particularly prone to triboelectric charging, ditto. You do not need a difference in the field along the cable, and in fact, when transmitting desired signal, there's no significant field along the cable- the triobo charges discharge across the Thevenin equivalent resistance of source and load in parallel, producing a spurious input voltage which is amplified by succeeding stages, ditto.
Now if you have a better explanation of this cable microphony which goes away when switching to PVC/copper, and it's based on physics, I'm all ears.
Now if you have a better explanation of this cable microphony which goes away when switching to PVC/copper, and it's based on physics, I'm all ears.
I was correcting a calculation based on an estimate made by fas42. He forgot that the dominant relevant impedance is the source, not the load.lemans23 said:
I am curious. How does charge move (to charge and discharge) without there being a current?
Not mine. I was merely correcting someone else's calculation from that estimate. I have no idea how plausible the current estimate is.SY said:
When SY gets the cable to me, we may find out. 🙂 Should be fun.
FWIW, I've tested a Noble 50K log pot with 9V DC across it and could get no microphonic effect at all going into a sound card. Will test again, just to be sure.
FWIW, I've tested a Noble 50K log pot with 9V DC across it and could get no microphonic effect at all going into a sound card. Will test again, just to be sure.
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