Condenser Mic Array Amplifier Circuit

[Bronston]

This is a bit out of my realm so forgive me if I don't seem particularly knowledgeable on the topic, it's only because I'm not. I have a system that controls most of the electrical devices in my home. The devices themselves are directly controlled by a atmega644p which is in turn controlled by my computer. I have software I've constructed in java that uses sphinx 4 to receive voice commands. Sorry long winded description, seemed necessary though. This all works perfectly except for one hitch. I need to have my stupid pc headset on in order to use the voice control system. This is obviously very limiting. My solution is to build an array of condenser mics to pick up my voice anywhere all through the simple little 1/8" jack on my computer. I have attempted this already but the mics where either not sensitive enough or too sensitive and all I got was garbage. I have run across an amplifier circuit that seems like it maybe the right direction but I, as I said, am sadly understudied in this arena. If I could get some solid direction it would probably make this entire project much more doable.

Here's the mics I have/would like to use.

Condenser Mics x 10
Mouser Part #: 665-POM-2744L
Manufacturer Part #: POM-2744L
Data Sheet: https://www.puiaudio.com/pdf/POM-2744L.pdf

I have some amplifier transistors I've robbed out of a couple surround sound head units as well, though their location escapes me at the moment. Just generally is there any chance of these being of any use?

Here's the circuit I was looking at. Is it along the right lines or not? If so would I put it at the end of the array or would I need one at every mic?



Thank you **broken link removed**.

 

[kak111]

POM-2744L is electret type 2-wire microphone
Standard operating voltage 2Vdc ( Max. voltage 10Vdc )

This is how to connect your microphone to supply.
Series resistance RL is 2.2k for 2V , 4.7k for 5V and 10k for 10V supply.



Needed preamplifier connected to capacitor Cs.

In theory you need pre-amplifier for each microphone,
but you can test what is the noise level when connecting several mic`s to one common pre-amplifier.

 

[Bronston]

Ok cool, thanks for the info. Can you go into a bit more detail on the preamplifier, or is that what the circuit itself is? Also do these mics look like they would be able to pick anything useful up if they were mounted on the ceiling, maybe 4-7 feet from the person talking?

 

[kak111]

more detail on the preamplifier,

try google "electret microphone preamplifier schematic"

do these mics look like they would be able to pick anything useful up if they were mounted on the ceiling, maybe 4-7 feet from the person talking?

Here is wiring for these microphones to PC or Laptop (, mic input in pc has inbuild voltage supply for electret mic.)
so you can test how sensitive they are and what is the best way to fix mic`s on the wall.

Hint: Fix mic on the wall, PC sound record ON , walk around room and talk. Listen and give points.

 

[kak111]

Wiring for single & parallel microphones to preamplifier.

 

[FvM]

If I understand your intention right, I don't expect, that mixing/adding the microphone signals from multiple rooms and locations serves the purpose. It will reduce overall signal-to-noise ratio by a considerable factor and possibly causing failure of a system, that works well with a single microphone.

For reliable operation, you would want to implement a kind of squelch or noise-gate functionality, that only activates a microphone channel above a certain sound level, or a mux that selects the channel with highest sound level. There may be still a problem if arbitrary interfering sound sources are present in a room.

 

[kak111]

For reliable operation, you would want to implement a kind of squelch or noise-gate functionality,
that only activates a microphone channel above a certain sound level,
or a mux that selects the channel with highest sound level.

I agree that this is the better solution

Especially when keeping only the channel with highest sound level open
and still continuous scanning other channel levels.
When spoken commands will be used band pass filter is needed for
selecting only the human voice spectrum.

But some comparison and testing is still needed to find out microphone mount and position on the wall.

My opinion is that it is possible locate two or three microphones in the same room and when
the right location has found and some signal phase shift done , it will reduce the interference level and
also the need for signal amplification.

 

[Bronston]

Alright awesome info, thank you very much. I ordered some sample LM741's before I made this thread. As soon as they come in I'll getting building. Thanks again.