Electret mics through mp3 speakers?

[jtrees]

I'm working on a project for the elementary school that I work at. We have a class observation system where people take these very old speakers (built in-house) and plug them in to a 1/4 in jack outside the classroom. The mics inside the classrooms, as far as I can tell, are electret mics, but they draw power from the speaker when someone plugs one in. We're trying to update the system a little bit to use portable mp3 speakers rather than the old bulky ones we have now as those are pretty much useless, but everything we've tried doesn't seem to work. We've tried using 3.5mm-1/4 in TRS adapters (both stereo and mono) and neither worked. We also tried rewiring the connection using a 3-conductor stereo phone jack from radio shack (basically seeing if it would work if the connection was just 3.5 mm) but that didn't work either.

Can anybody offer any advice? We're trying to find a solution that doesn't break the bank and so far we can't seem to find anything that actually powers the mics and gets sound from them. Is the problem with the mp3 speakers or with the connection? or both?

Thanks in advance for all your help! I'm a bit of a novice when it comes to this so any help will be great, thanks!

[DVDdoug]

I assume your "speakers" have a preamp, amplifier, and possibly a mixer built-in?

I think you are missing the preamp.

With "MP3" speakers (I assume these are speakers that plug into an MP3 player or computer) you don't have the preamp.   The signal out of an MP3 player or computer is about 100 times the voltage you get out of a microphone.

The least expensive solution (without building something yourself) would be a small mixer something like this.   Just make sure you buy one with a microphone input.

...as far as I can tell, are electret mics, but they draw power from the speaker when someone plugs one in.

That would be unusual.    Electret (and condenser mics in general) do requiere power.   Dynamic mics don't need power.   Computer mics are unique.  They run on 5V supplied by the soundcard.   I don't know of any preamps, mixers, or PA systems that work with computer mics.  Studio condensers (with XLR connectors) run from 48V "phantom" power, supplied by the preamp, interface, or mixer.  Stage/performance condensers (with XLR connectors) usually have a built-in battery, and sometimes they optionally run from phantom power.

[jtrees]

Yeah I was wondering if it was because the speakers didn't have something... But the old speakers don't seem to have an amp or anything, basically the connection comes in, goes to a little (incredibly crude) circuit board, then from there splits off to the batteries, and a power switch. I do know at least that the mics draw power from the speaker. I've confirmed with the IT department here though that the mics draw power from the speakers, but they're too busy to help us with anything else so they said we were on our own coming up with a solution. And I know that electret mics can be plug-in powered, but these are set up basically the opposite way, so that they draw power from whatever is plugged into them.


Do you think it would work if I rewired it so that the mic actually plugged in to the speaker, rather than the other way around? Not sure if that would work, or if its even possible, but I'm pretty much up for any solution at this point

Of course maybe the mics are set up to directly connect to the battery when the speaker hooks up... I'll have to check that out to see for sure... in that case, maybe just buying a small separate power supply for the mics would work best?

If pictures of the connections would help I can get those too

[jtrees]

Yep found out it's the preamp... the ugly old speakers had an amp inside them and so we're getting new preamps so it'll work with the new little speakers... Thanks for the help!!!