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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Thanks, that answers my question. posted by Commuteman on January 12, 2004 at 17:13:01:
Peter: "" Have I got this right:
You posted that original message as an analysis to suport the contention that the pizoelectric effect cannot, by itself, cause an audible effect as a result of reasonable mechanical stimulation.Correct? ""
When I wrote that back then, I was focussing primarily on the ability of a SPEAKER cable to be sensitive to piezo effect. In re-reading my post there, I see the sentence "a typical speaker has about 1% conversion efficiency.....that is the only place where I clearly indicate what wire I am talking about, and that there is no power gain between the piezo stimulation, and the speaker load.
I then, on a whim, tried a simple calculation for an IC, using Bruce's 200 uV level (the only measurement performed at the time). Since source impedance was unknown, I still had to use total energy.
I am quite confident that piezo is unimportant for a speaker wire, and that was the intent of the simple calculations.
For IC's, Bruce's newer test data with 1 volt into 10 Meg would require re-calculation of effect, and he provided several load points to evaluate the source impedance.
Armed with the source impedance, it is possible to model the piezo as a known VOLTAGE/resistance error source (well, for finger blips at least), and see just how much of an impact it will have on the overall system.
An even better experiment will be to measure the piezo pickup in a known spl environment. To control for confounding effects, one coax cable needs to be in the room, with the sound impinging on it, and a second, reference one, needs to be right next to it, but enclosed within a vacuum to eliminate vibration excitation while allowing any extraneous e/m pickup (for example, the modulating field of a woofer) to be subtracted. A 1/4 inch thick acrylic tube can handle the vacuum without shielding at any level the mag field pickup we wish to cancel, while filled cement blocks at either end will provide a sufficient mass for wire anchoring at either end to not vibrate the wire. It will not matter how much the tube vibrates in the middle, sound does not travel in a vacuum.
As to low level signal cables being piezo sensitive...I think everybody has experienced it..and I think my experience was more one of a high residual mag field enviro.
JR, unfortunately, did not ask any questions for elaboration...he just reacted without all the information..he just wanted the post it'self, which I presented.
Thanks Peter..you ask reasonable questions..
Cheers, John
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Follow Ups
- Elaboration - jneutron 07:06:36 01/13/04 (0)
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