Electret mics, can 2 or more be wired in parallel?

[gary350]

I accidently ordered 5mm mics not 10mm mics. 10mm mics are several times louder than 5mm. 5mm is not working on my project can I wire several 5s in parallel to work as good or better than 10mm?

 

[ronsimpson]

Watch the phase! Can you tell pin1 from pin2?
Solder two together. Send a low frequency tone into the mics. Two mics, if wired right, will be better. Two mics if wired wrong will be much worse.

 

[gary350]

I know I tested a 5mm mic compared to a 10mm once it did not work well. I know I tested 2, 5mm mic in parallel to a 10mm it did not seem to works any better. Today I tested 3 of the 5mm mics in parallel to a 10mm mic it is noticeable louder than a single 5mm pic. Next I tested 8 of the 5mm mics in parallel to a 10mm pic it work fine in parallel. 8 of the 5mm mics are noticeable louder than 3 mics in parallel but still no where as loud as 1 single 10mm mic. Next thing to try 16 mics in parallel to see how loud it is compared to a single 10mm mic. As far as I am concerned 5mm mics are worthless compared to 10mm mics. I have a pack of 50 mics maybe I put all 50 of the 5mm mics in parallel on a PC board see how it works maybe it will finally = a 10mm mic. This will have to wait about 2 weeks too many other things to do at the moment.

I am running a 386 ic on 8AA batteries to some average quality stereo ear phones. Batteries all test 1.6v = 12.8v.

 

[audioguru]

I saw and heard very bad sounding ceramic mics about 60 years ago so today I looked in Google. Knowles show the horrible frequency response for their ceramic mics that are no longer available.
Why don't you use an excellent sounding and inexpensive modern electret mic?
Why do you have the mic and earphones together? A hearing aid?

 

[gary350]

I made a mistake I have electret mic not ceramic. The 10mm mic has very good sound and many times louder than the 5mm mic. I should probably throw the 5mm mics in the trash they are a waste of time.

 

[audioguru]

I got a 5mm electret mic from a cell phone and it works perfectly. Most of my other electret mics are 10mm and they also work perfectly.
This thread has no schematic so we do not know what resistor value powers your electret mic.
We also do not know the gain setting of the LM386 power amplifier.

 

[rjenkinsgb]

You cannot go just on the physical size.
Different makes and types can have vastly different sensitivities and characteristics.

I have some ebay ones that give next to no output, and some bought from such as Farnell that give a very high output, in comparison.

 

[audioguru]

Since he has a bag of 50 microphones then they must be very cheap with extremely poor quality.

 

[gophert]

I made a mistake I have electret mic not ceramic. The 10mm mic has very good sound and many times louder than the 5mm mic. I should probably throw the 5mm mics in the trash they are a waste of time.

You cannot go just on the physical size.
Different makes and types can have vastly different sensitivities and characteristics.

I have some ebay ones that give next to no output, and some bought from such as Farnell that give a very high output, in comparison.

Agree. Some of the smallest on digikey (0.1" diameter) have some of the highest sensitivity.

 

[gary350]

Here is the final circuit drawing. The PC board I experimented with is an older board it looks like all the parts were updated. I have several parts soldered on the bottom side of the PC board. IC part number is 386n-1. This old board needs to be stripped and start over it will be good for my tone control circuit.

 

[Nigel Goodwin]

Well I always think it's a horrible idea misusing a small power amplifier instead of using an opamp, and in this case even worse as adding passive tone controls means you make a large signal loss through the tone controls.

 

[audioguru]

You do not need a capacitor in series with pin 3 on the LM386 because it already has a resistor to ground in it.
If you connect left and right 32 ohm earphones in parallel to make 16 ohms then the power from the LM386 will damage them and your hearing.
With a 12V supply, an LM386 output into 16 ohms is shown in its datasheet as 10Vp-p which is 0.78W RMS so each earphone gets 0.39W. But 0.1W is extremely loud and is damaging your hearing.

The 100uF capacitor value is too low since it cuts 100Hz and all lower frequencies.
Why do you have an amplified microphone and earphones?

 

[gary350]

You do not need a capacitor in series with pin 3 on the LM386 because it already has a resistor to ground in it.
If you connect left and right 32 ohm earphones in parallel to make 16 ohms then the power from the LM386 will damage them and your hearing.
With a 12V supply, an LM386 output into 16 ohms is shown in its datasheet as 10Vp-p which is 0.78W RMS so each earphone gets 0.39W. But 0.1W is extremely loud and is damaging your hearing.

The 100uF capacitor value is too low since it cuts 100Hz and all lower frequencies.
Why do you have an amplified microphone and earphones?

There is only 1 ear phone.

 

[gophert]

There is only 1 ear phone.

Yes, but, WHY is there an earphone? What, exactly are you making?

 

[ChrisP58]

Not speaking from experience, but I think that the array of microphones, when wired in parallel, will likely be a bit more directional than a single mic. That is because the signals will add more for sounds that reach each mic at the same time. Signals from off axis will reach each mic at different times, and will have a tendency to cancel each other instead of adding.

Of course, this effect will vary with frequency.

 

[shortbus=]

Yes, but, WHY is there an earphone? What, exactly are you making?

Inventing the hearing aid?

 

[audioguru]

My hearing aids match the normal-for-my-age (75) high frequency hearing loss which uses treble boost 3 times more than a simple tone controls circuit.
They have selectable noise reduction, extra sensitivity, left, right, front and back directionality and muting.
Their tiny inexpensive batteries last for 2 weeks.

 

[gary350]

This is just a fun hobby project. I have a package of 50 mics I am trying to find a use for or throw them in the trash. 5mm mics are almost worthless but 10mm work excellent. I can hear every bird in the trees. I can hear people talking a city block away like they are standing right next to me. I am probably wasting my time it makes more sense to throw 5mm mics in the trash. I could sell package of 50 mics on ebay to get rid of them. It is more FUN to experiment.

 

[audioguru]

Lots of people find 50 defective mics in the trash then sell them on ebay. I guess you bought some.
You are lucky that you have not be made deaf by the power amplifier.

 

[schmitt trigger]

I find the idea of experimenting with a microphone arrays actually quite appealing.
I encourage you to continue.

Right now I am way too busy to type a lengthy reply, but I will give you a little homework: Google the term “summing amplifier” and look for the datasheet of the TL072 opamp