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Multiple Microphones
Multiple Microphones
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Old 29th March 2019, 07:08 AM   #1
StevenStanleyBayes is offline StevenStanleyBayes  Canada
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Join Date: Jan 2012
Location: Ottawa
Default Multiple Microphones

Before all, please, note : some audiophiles may not prefer to parallel microphones because, although made by the same manufacturer and processes, there are tolerances which may lead to slight non linearity. I hope this is negligible.

I have made a multiple microphone with sixteen Electret Condenser Microphone capsules.

I still wait for a 500K dual potentiometer which has been ordered. The device was tested without such with direct wire connections instead.

The document is not finished, there are more explanations to be made and pictures, which would probably be made once the dual potentiometer is installed as well as labels.

The document will be updated.

I would like to publish this document now, although not fully completed, because the project has been an obsession and a dream which I have been able to make a reality.

Here is the document :

Multiple Microphones - Google Drive
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Old 31st March 2019, 06:34 AM   #2
mchambin is offline mchambin  France
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Here is a best introduction to microphone preamplifier design:
http://www.thatcorp.com/datashts/AES...ic_Preamps.pdf
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Old 1st April 2019, 05:09 PM   #3
GuitarFogie is offline GuitarFogie  Canada
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Just curious as to how you plan to use this project? Have you thought of building individual mixer circuits for each mike (Basically a board) and sending them to the amp circuit? You may want to check out how "individual string pickups" are used on guitar synthesizer circuits.
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Old 1st April 2019, 05:31 PM   #4
cbdb is offline cbdb  Canada
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There is no point to this unless i missed something and your building a 5 channel mic for surround recording.Get a better mic/ mic preamp if your mic is not loud enough.
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Old 2nd April 2019, 10:05 AM   #5
DF96 is offline DF96  England
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Naive paralleling of microphones will give a rather peculiar polar diagram. This project seems pointless.
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Old 3rd April 2019, 03:13 PM   #6
mchambin is offline mchambin  France
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The joint Texas Instrument Application note is good reading.
A good point on parallelling 16 microphones is about noise.
This gives a better Signal / Noise ratio.
Signal ( correlated ) increases x 16 while noise ( un-correlated ) increases x 4.
So you get S/N x4 ( +12dB ).
This is only true for pressure waves in front, for pressure waves angled the signals don't simply add, they are phase shifted an effect which is more at higher frequencies.
16 amplifiers would make no difference. These behave like current sources, when paralleled they add as would do adding 16 amplifiers outputs.
The Op-amp used by Texas Instrument is perfect for this electret mic, as calculated in their detailed AN. Even better from the noise point of view whith 16 // electrets.
Acoustic of 16 //. The pick up pattern will be peculiar, with many lobes in the high frequencies.
You can experiment with various geometries for various effects.
The mics in line, close together.
The mic in line, spaced.
The mics closely grouped 4 x 4
The mics as close as possible. Hexagonal, honey comb like.
You should get strong directive effects. Have fun.
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Old 7th April 2019, 09:47 AM   #7
StevenStanleyBayes is offline StevenStanleyBayes  Canada
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I shall try to make an answer to all concerns made before this answer.

1. An updated, still, not ready file has been uploaded.

2. I still wait for the dual 500K potentiometer.

3. Paralleling microphones increase sensitivity and signal to noise ratio. Such sound may not be available from a single microphone with high gain.

4. The problem with paralleling any microphones, say, professional ones, is the microphones are not exactly the same which affects the non linearity error. However, when two microphones are played on two different stereo channels, any difference between their phases will move the sound in a 3D way.

5. This project does NOT need separate mixer, because, the microphone output is already added ( mixed ) by their parallel configuration. However, a better way may be to buffer each microphone with a buffer amplifier and then to add their voltages with an adder. Thus, 17 amplifiers are needed to achieve this. In this project, the transistors ( microphones are buffered by a JFET internally ) are just paralleled and the current of each is added to make a general current which is then converted to a voltage by a current to voltage converter, a. k. a. a transconductance or transimpedance amplifier.

6. This microphone has a built in preamplifier and can be directly connected to an amplifier input or an amplifier microphone input or a PC. Phantom power is not necessary. Any phantom power provided by a microphone phantom power input is ignored by the output capacitors. This microphone has three outputs, two of which are the same, just provide a different socket :

A. 1 / 4 inch mono output of the preamplifier
B. 3.5mm dual channel mono ( stereo with the same channels ) output, the same as A.
C. Output directly from the microphones without any preamplifier ( phantom, power is not necessary and will be ignored when present ). Please, note, the switch which switches the output capacitors on or off must be in on ( 30uF ) position.

I hope this answers the questions.
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Old 7th April 2019, 12:30 PM   #8
StevenStanleyBayes is offline StevenStanleyBayes  Canada
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A very important application is the ability of this microphone to amplify the sound so well, so, the microphone can be positioned anywhere and the speaker does not need to be in front of the microphone. This is excellent for Skype communication where the speaker can be anywhere in the room doing anything and the microphone can be anywhere and does not need to be close to the person.

Of course, when the microphone is connected to an amplifier with speakers, high gains may cause a microphone feedback. This is not a problem with a PC or headphone where there is not any speaker to " talk back " to the microphone and thus cause a microphone feedback.

For guitar and singing, the same applies : the microphone can be away from the singer and guitarist. One application may be where the guitar and the voice are picked by a single microphone which may be in the middle or closer to the quieter guitar to get the voice and the guitar equally.

Also, voice may be recorded at higher acoustic quality when the microphone is away from the singer.
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Old 7th April 2019, 01:57 PM   #9
DF96 is offline DF96  England
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Could you explain how paralleling microphones somehow increases nonlinear distortion?

Could you explain how a more directional microphone can be positioned anywhere?
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