Professor Hathaway: "I notice you've stopped stuttering." Student: "I've been giving myself shock treatments." Hathaway: "Up the voltage."Don’t worry Brad, they are experienced professionals and seasoned amateurs.
One more “kick” is what they are asking for (“give me more baby!")
George
from Real Genius, 1985
In a loudspeaker there are powerful magnetic fields.
The capacitors spoken of here have aluminum inside.
I would expect it is the magnetic fields and not the acoustic SPL that are the real cause because aluminum are paramagnetic.
You should source a copper based capacitor (identical value to the aluminum) and perform your measurements again and compare.
Alternatively: You can use two powerful neodym magnets and put the aluminum capacitor in its own un-modulated magnet field inside your speaker and then measure - this way you will also see if it is the acoustic SPL or magnetic modulations that cause the problem.
I use copper or silver mica capacitors if possible due to the issues aluminum will give even without powerful magnetic fields.
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Now I got it (better than never).
Scott and you were meaning to use microphone and EM sniffer both at a distance from the capacitor.
That’s OK then. Time difference is in the ms range.
In such a case, the excitation circuit I posted is probably not a good choice, as it will generate a lot of unwanted signals, acoustic and EM (but one can get rid of the triggering transformer and replace the xenon tube with a temporary shorting contact).
See here for a three-part video description (it is almost the same circuit)
Camera Flash Circuit and Nixie Tube Tutorial (Part 1/3) - YouTube
Camera Flash Circuit and Nixie Tube Tutorial (Part 2/3) - YouTube
http://www.youtube.com/watch?v=RziYdY1ovsM
Flash circuits in digital cameras use no transformers anymore. There are plenty of such dirty cheap cameras around for experimentation.
Ed and all, I appreciate when you are correcting my english (m F’rs !
)George
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If I may, SY means that for the magnetic field strengths a speaker unit can generate, either paramagnetic or diamagnetic materials have their relative permeability so close to zero, that they can be treated as “non magnetic”
At magnetic field strengths that jneutron is working with and with superconductors, these differences may matter.
George
I don’t have access to a calibrated AC-DC gauss meter anymore.
I have probed with a coil probe close to an unshielded driver and I can see on the scope the result of AC magnetic field variations when music signal feeds the speaker coil but I can not provide field strength numbers.
I have to build a Helmholz coil for to calibrate the sensing coil & meter circuit.
George
First, the yield strength of aluminum has no meaning in this physical example. The jellyroll construction technique has very thin aluminum foil wrapped in a cylinder. The deflection of the aluminum will be dependent on the thickness of the underlying structure as well as the modulus of the plastic.
Second, you are confusing low signal level high spl vibration induced changes with an application which has relatively high voltages and very low impedances. It is certainly not scientific to assume that because an effect exists, it happens everywhere to any significant level. You may as well include the aluminum grain boundaries and quantum fluctuations if your intent is creative writing.
I note that you still resist any attempt at elimination or control of the confounding physics effects which severely compromise your test. Why?
I vote parody..
I assume you meant relative permeability so close to 1? Or did you mean absolute permeability so close to 4 Pi 10e-7 henries/meter?
Yes, you may.
The external magnetic field of a driver is the summation of the leaked dc field and the leaked AC field. This is a very simple thing to see, just attach a small coil to a scope probe in and wave it about the back of a magnetic structure while it is being exercised.
Remember, all solid conductive materials like a typical magnetic circuit of a speaker, will attempt to exclude the time varying flux to some degree. The effective parasitics of the magnetic circuit will go up with frequency.
Excellent!!!
jn
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You need to remember that truth is stranger than fiction.SY said:
As I suggested (elsewhere? I forget which thread) this could simply be learning words but not their meanings. Something which non-scientists never seem to do is estimate the likely magnitude of their proposed effect. When someone else does a back-of-envelope calculation for them to demonstrate that the effect is (usually) vanishingly small they then interpret this as 'proof' of the sensitivity of human hearing.
DF96 wrote "Something which non-scientists never seem to do is estimate the likely magnitude of their proposed effect."
Reminds me of the guy who proposed to send helium balloons aloft over the Antarctic with a contraption attached that would generate ozone. Someone (a scientist) shot the whole thing down when he explained that to fill the ozone hole required c. 40 million tons of the stuff.
Reminds me of the guy who proposed to send helium balloons aloft over the Antarctic with a contraption attached that would generate ozone. Someone (a scientist) shot the whole thing down when he explained that to fill the ozone hole required c. 40 million tons of the stuff.
To clarify, a spark generates an acoustic event my intent was to use the capactor under test as a "microphone" several meters away and the electrical and acoustic events are several milli-seconds apart easily windowed for analysis. The functional form of the acoustic event is well known and deconvolving it with the output is easy.
A grill starter (with the button placed well behind the gap) works fine. Available at Home Depot with nice long leads. I made the gap with a couple of pieces of #32 wire about 5mm apart.
I have published the results elsewhere using this with a Nakamichi CP3 microphone (from back in the days when the little response chart actually was THAT unit) excellent conformance to .5dB or so and very repeatable if you know what you are doing. The only question is aging of the electret, it was 40yr. old but the absolute resposivity was still almost exactly on.
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