Have a small microphone mixer
I've been using a couple of dynamic microphones on it, but I wondered if it was possible to either get a tie-clip microphone (these seem to be electret condenser) which can be plugged straight in OR match the different technologies somehow.
Thanks, Midge.
If you use an electret mic with built in battery then you should be able to plug it straight in.
Cheers
ian
If the electret has a built-in FET buffer, all you'll need is power for the FET.
Otherwise the Audiomate input impedance is too low. ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
As an aside, does the standard explanation of how electret mics work bother anyone but me? It's usually stated that the 'frozen in' electric polarization in the material works just the same as the applied voltage in a real capacitive mic. This is of course nonsense--charges such as air ions migrate around and eventually neutralize any E field external to the electret material, so that waving it around does nothing whatever. (Leakage--that's why you have to keep the capacitance mic's supply connected for it to work, duh.)
The reality appears to be that they work by a combination of the piezoelectric effect (like a quartz crystal) and the variation of capacitance with stress (like coaxial cable with a DC voltage on it).
Any comments from audio folks?
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal
I've used them many times in hearing-aid chip designs, but I have no idea of how they actually work. The leader, in hearing-aid usage is Knowles...
But I've also used a MIMS equivalent (Akustica) which was simply a capacitor biased with a _very_high_valued_ "resistor", powered from a
4X charge-pump (my part of the design). ...Jim Thompson-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
I just did a design for a startup making radiation sensors from conductive polymers--it used a $5 CCFL inverter with a bridge rectifier and a rail splitter to form half of the readout bridge. It makes 600V from a 5V supply. There are a lot of things you can do with those, for very little dough. (Maybe even make capacitive mics.)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal
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electret
I don't the luxury of a wall socket for my hearing-aid designs ;-) ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
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Your customers just aren't plugged in. (This isn't a wall socket application either.)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal
Some piezoelectric materials do need to be polarized to work.
I suspect that the "charge frozen in" explanation is valid to the extent that anything else could be without going into the details of the physics, and it has the desirable property that it confuses people into shutting up while still using the device correctly.
Do you accept the "trapped charges on a floating gate" model of EEPROM behavior? How is that different from the "frozen-in charges" of the piezo microphone?
-- Tim Wescott Wescott Design Services
Thanks for the advice guys.
Midge.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
Why is frozen electric field in plastic any more difficult than frozen magnetic field in a whatsit to make a magnet?
Yeah but can you easily neutralise the charge trapped in the plastic?
That too.
Grant.
That's the one I wanted to mention too :) What gets me is the current
3bit per cell technology, reliably trapping one of eight voltage levels in the memory cell gate, and remembering that level for years...Grant.
I'm not denying the existence of electrets, either the PVDF plastic ones or the floating-gate CMOS ones. Inside the material, charges aren't free to migrate around, so there's no worry. It's outside, where air ions and charged dust can accumulate, where you can't hold a static charge for too long. (Rubbing a toy balloon on your hair can make it stick to the ceiling, but eventually it unsticks itself as the charge leaks away--or air ions arrive to neutralize it.)
The same is true of magnets, except that there is no such thing as a magnetic monopole--i.e. the magnetic equivalent of free charge doesn't exist. That's why magnets continue to produce a field external to themselves, but electrets don't.
I think you're probably right that it's a "Mr Science" type explanation, designed to shut people up rather than to actually answer the question.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal
Regarding presumed "frozen in" charge.. About 50 years ago, in high school, there was this "true" rumor of a related experiment: Take a sheet of glass and place a metal plate on each side to make a capacitor, then charge it (2KV to 20KV if i remember correctly). Disconnect completely and then remove the glass sheet. Measure the voltage (virtually zero). Remove volt meter, replace the glass sheet and measure again. According to the story, one reads near the original charging voltage. But it gets better.. Short this cap and verify zero voltage. Wait..(minutes, i think an hour max i think) then re-measure and find a rather shocking (literally) voltage present.
** Naturally, that second aspect is well known - most especially to TV repairmen dealing with those CRTs.Jim Thompson a écrit :
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How about an ear plug?
-- Thanks, Fred.
Mylar tape is made with a charge holding the sticky on. You can use this to make an electrostatic speaker. All you need is a step up transformer. Unfortunately the sticky weighs down the tape too much for efficiency. I tried taking the sticky off and the charge disapears. I wonder if that great roll of OD military mylar tape I have from the 60's still works.
greg
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