Cheap conferencing audio -or- help with microphone basics

Dave Ungar

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Apr 2, 2021
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I'm trying to help a nonprofit put together a meeting conferencing system on the (VERY) cheap. Essentially Zoom + omnidirectional ambient microphones distributed throughout the room. So - I have a 4-mic mixer (with phantom power) that hooks up to a laptop via USB. In principle, this should do the trick.

A quality cardioid microphone produces enough signal. But the ambient room mics (3.5mm plug mic, made for PC or small device) are SUPER faint. I don't understand how mics work quite well enough to know if this is doable. Is there a way to raise the gain? lower resistance?
mic.png

I know there's an issue of cheapness here - but I expect that has more to do with sound quality than gain & volume. I mean, a cheapo mic can still pick up a lot of sound. So I'm looking for help here on either:
1 - how to attach multiple room mics to a computer/ zoom
or
2 - how to raise the gain of these mics going into the mixer. (Or explanation of why it doesn't work as I think it should.)

Thanks for your ideas!
 

Dave Ungar

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Apr 2, 2021
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OR .. (maybe?) tell me how phantom power works -- maybe I need to understand how to send the power to the mic through a 3.5mm plug. What's the proper wiring/ pin configuration?
 

Caleb Dueck

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Jan 11, 2011
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What about USB mics that work together natively, like Jabra?

Much more than that will require a small DSP, which works great but kills the budget.
 
The mixer takes a 1/4" mic or a XLR input. So I'm using a stereo>mono 1/8">1/4" converter. (Headphone converter.) Convoluted? Yes!
I'm not aware of any mixers with 1/4" mic inputs that are new enough to have USB. On most modern gear, the 1/4" inputs are either line-level, or intended for use with instrument pickups (and noted as such). Given that you are getting very low input levels, I'm guessing your mics are plugged into inputs expecting line level signals
 

Dave Ungar

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I'm not aware of any mixers with 1/4" mic inputs that are new enough to have USB. On most modern gear, the 1/4" inputs are either line-level, or intended for use with instrument pickups (and noted as such). Given that you are getting very low input levels, I'm guessing your mics are plugged into inputs expecting line level signals
There is a port that takes XLR -or- 1/4". download (6).jpg

I found some information that helped. The ambient mics use 'plug-in' power, which is about 5 volts. (XLR uses 48V phantom power.) So I had to buy an adaptor that not only changed 3.5mm to XLR, but also converts 48V to 5V. (Not sure if I can DIY-make a plug like that, but I can buy one for $14, so that'll do!)

@Caleb Dueck - Thanks for your suggestion. I looked into that.. Luckily I found another option. I was a little reluctant to go with multiple USB mics because that seems to leave more troubleshooting to the user. (That is, they might have to select multiple settings on the laptop - whereas analog mics are a little more plug & play (once you figure out how to hook them up. ;) )
 
There is a port that takes XLR -or- 1/4". View attachment 209455
Yes, but note that on those connectors, there is no guarantee that the XLR and 1/4" inputs go the same places, and the mixers I've used with those style connectors had either line or instrument inputs on the 1/4" connectors (usually line input) and mic inputs on the XLR.
 
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Dave Ungar

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Yes, but note that on those connectors, there is no guarantee that the XLR and 1/4" inputs go the same places, and the mixers I've used with those style connectors had either line or instrument inputs on the 1/4" connectors (usually line input) and mic inputs on the XLR.
ah - gotcha. Thanks. That may explain why things weren't working as expected - eg I'd at least have expected phantom power to blow out the plugin-power microphone. :) ....but not if it's actually line-level. Makes more sense that way.