Hi, I am just interested in the idea of paralleling electret mics. I Have built a couple of recording mics for instruments, and they work extremely well. However I want to make a mic for group singing and am looking for info on how to use more than one mic so as to cover at least a circle of 180 degrees and get the same response all round. I will have to experiment with the preamp I use untill I get the results I need. As is with everything good results take time and lots of experiments, and at times smoke.

 

A cardioid pickup pattern is the classic pattern you are probably after. Good sensitivity over 180° while suppressing the back of the microphone.

One cartridge in the right enclosure should give you what you need, no need to parallel cartridges.

May I suggest browsing the Sure microphone catalog?

 

Hi Dick, Thanks. I have normal sHure mics, The standard basic sure that everyone uses. I actually prefer AKG mics and have moved over to those. My idea is this. I sometimes work with choirs and they often have a small group that will sing together, and I want to be able to capture all the voices in the group. Sometimes the person on the end sings softer than the one in the middle, and as I am working in a live environment I need the mic to not be super sensitive as I need a good amount of head room.

The original design of the mic preamp I use was designed for outside recording and would pick up a whisper at least 4 meters away - not good for live recording in a hall. So I had to find a way to attenuate the signal as much as I could with out distorting or clipping. All the changes had to be made inside the circuit as it is phantom powered. Also the sound mixer I use is a SOUNDCRAFT SIGNATURE MTK 22 CHANNEL. The input pre-amps are super sensitive and the gain had to be on infinity just to handle the original design.

I now have got the signal down enough to give me the head room I need with out feedback. So my thinking is to make a semicircle of mics facing the voices. With a damping shield behind them to prevent any noise from the audience. The AKG mics I use are D5 . If I remember correctly the shure mics are SM58S.

 

You really want to get into the nitty-gritty of the circuit, now I understand that. I have changed the title if this thread accordingly.

Do you want to parallel cartridges or microphone assemblies? I have not used electret mics in a studio setting (it has been that long) so I am not familiar with the interface. Can you point us to a cartridge for complete microphone as an example?

 

I want to parallel the cartridges. The schematic I am using as the interface is attached. I got the original from the website of Elliot sound products. https://sound-au.com/project93.htm. The cartridges I am using are standard off the shelf ones.

 

Here is what the board will look like when etched. right now I am using protoboard. The layout and size is virtually the same.

I want to parallel the cartridges. The schematic I am using as the interface is attached. I got the original from the website of Elliot sound products. https://sound-au.com/project93.htm. The cartridges I am using are standard off the shelf ones.

 

As the output is a jfet drain, it is basically a constant current source. Just connect them in parallel.
But as @DickCappels said in post #2, there's no point - the electret condensor inserts you mentioned are omnidirectional.
[EDIT] I suppose it could be argued that putting two in parallel increases the noise by 3dB (because the two noise sources are incoherent), but because the audio signals are coherent sources, it increases the signal by 6dB, so that the SNR improves by 3dB.
But if you wanted a low-noise microphone, I wouldn't start with a device intended for a telephone handset.

 

Another complication is that the JFET in the cartridge needs a resistor or at least a current source. Put too many load resistors in parallel and that eats up sensitivity. Not sure connecting the drains together and using a current source would ok from a noise standpoint.

 

As the output is a jfet drain, it is basically a constant current source. Just connect them in parallel.
But as @DickCappels said in post #2, there's no point - the electret condensor inserts you mentioned are omnidirectional.
[EDIT] I suppose it could be argued that putting two in parallel increases the noise by 3dB (because the two noise sources are incoherent), but because the audio signals are coherent sources, it increases the signal by 6dB, so that the SNR improves by 3dB.
But if you wanted a low-noise microphone, I wouldn't start with a device intended for a telephone handset.

Depending on the distance between microphones, phase of the source signal could lead to some frequency response anomalies. In all my time doing sound reinforcement and live recording I never used a set of hot omnis all at once. It would have played havoc with the desired signal.

I may just misunderstand the situation and goal, but I am not sure why a cardioid or supercardioid of good quality isn’t better (in the absence of active signal processing).

 

This is nornmally done with multiple mics and a mixer.

Bob

 

Paralleling mics may create phase cancellations and other undesiarable phenomen (@Yaakov is correct). If you were to go ahead this plan, I would individually buffer and go into separate channels so you can control this.

 

Why would any

I sometimes work with choirs and they often have a small group that will sing together, and I want to be able to capture all the voices in the group. Sometimes the person on the end sings softer than the one in the middle

in that case you need multiple microphones. If you have an excellent quality 22 Channel mixer, and some extremely good Shure and AKG microphones, why would you possibly want to cobble something together out of noisy, mediocre quality telephone handset microphones?

 

Hi, All that has been said I have read about, and yes I have a mixer etc, however working with a limited budget and limited channels on my mixer multiple mics are not always the option. I have read of the more expensive mics using two cartridges. My daughter uses a small zoom h1n mic for recording her practices with her cello, and due to the cv19 issue, her music classes are all on line. this mic has two cartridges at 45 degrees from each other. From what I have read putting more cartridges gives me a larger diameter. Right now this is just an idea, I still need to perfect the ones for instrument recording like drums, piano etc. I need to try to get them to be more directional. As many of you all say, It may just be better to keep the design as is, however it is good to bounce ideas of others who know more than one self, and that is what I am doing, just to learn and understand.

 

Two microphones, both at 45° To the main direction the sound comes from is a Blumlein pair.
Most of those condensor microphone inserts are omnidirectional. To make them anything other requires a vent to the side of the diaphragm that is currently sealed.

 

Two microphones, both at 45° To the main direction the sound comes from is a Blumlein pair.
Most of those condensor microphone inserts are omnidirectional. To make them anything other requires a vent to the side of the diaphragm that is currently sealed.

Ok thanks that is interesting. Now I have a bit more understanding. Will keep on experimenting and see what I achieve. Thanks for the input.

 

Depending on the distance between microphones, phase of the source signal could lead to some frequency response anomalies. In all my time doing sound reinforcement and live recording I never used a set of hot omnis all at once. It would have played havoc with the desired signal.

I agree that more than a single microphone will seriously mess up the frequency response. Echoes might also might caused.

 

I agree that more than a single microphone will seriously mess up the frequency response. Echoes might also might caused.

Ihave read that if used, they must not be too close together. I have seen a set of mics made by Earthworks that is used for miking a piano. I like the idea and I am looking into making my own. I think though I will have to build a small mixer to handle them. I have a circuit and this design also has the function to correct for the effect of phasing. Of the shelf mixers do not have this function and I could make it such that the settings etc of the eq etc are done and then closed inside to prevent anyone changing them. This too will be a long project that will keep me out of trouble for a while.

 

Hi, All that has been said I have read about, and yes I have a mixer etc, however working with a limited budget and limited channels on my mixer multiple mics are not always the option. I have read of the more expensive mics using two cartridges. My daughter uses a small zoom h1n mic for recording her practices with her cello, and due to the cv19 issue, her music classes are all on line. this mic has two cartridges at 45 degrees from each other. From what I have read putting more cartridges gives me a larger diameter. Right now this is just an idea, I still need to perfect the ones for instrument recording like drums, piano etc. I need to try to get them to be more directional. As many of you all say, It may just be better to keep the design as is, however it is good to bounce ideas of others who know more than one self, and that is what I am doing, just to learn and understand.

The microphone on a Zoom recorder is an XY stereo microphone designed to provide a stereo image. The microphones are cardioid.

 

The microphone on a Zoom recorder is an XY stereo microphone designed to provide a stereo image. The microphones are cardioid.

Ok, did not know that. Thanks. I have a lot to learn.

 

Hello Ed, I am a retired electrical engineer 000s of volts and MWatts, with a strong envy for the small end of the scale and a self taught with such items as op amps. I have an old English sports car with soft top, which has a lot of road and exhaust noise in the cabin. I have not been successful with my efforts to develop a sound canceling system using one electret microphone in the boot with an amplifier and speakers separate from the radio in the cabin.
I wonder if you would share with me the schematic circuit of the amplifier you have developed ? David <Mod: deleted email, avoid spamming.E>