Sensitive Microphone Array

Microphone design is specific to the application...The type and nature of the sound you want to amplify will determine the type of microphone system you would employ...Just wiring several microphones together does not guarantee quality of sound, and may in fact result in poor results....

http://en.wikipedia.org/wiki/Microphone

Yes, and no.

A, "highly sensitive microphone array" will require definition.

We'd need the sensitivity/frequency response of each individual element by itself and the desired sensitivity of the array afterward.

Sensitive as in being able to detect very quiet sounds. I thought that soldering several condenser elements in series or parallel would make the output voltages stronger.

Condenser mic do not produce voltage. The capacitance is measured by applying a bias and measuring the charges flowing from the bias.

Magnetic pick up mic do produce voltage like a small generator.

The sensitivity of your mic is more complex than adding surface. You have also impedance and bias issues, noise ...

Note that there are some mic elements available that can detect a fly fart. Simply look for the proper manufacturer and use a good amplifier. You will also need a room where the ambient noise is so low that you will ear your own heartbeat.

You say, "You also may get reflected sound off of walls or other surfaces."

I say you WILL. And their phase will have been altered again.

OP will need to define, "very quiet sounds". Anechoic chamber, or in the woods sounds?

Yes, but is so complex due the surface material type and its shape, proximity, amplitude, frequency, etc.

Then there are diffraction effects, which add or subtract from the reflected wave.

So, without getting too lost in the minutia of the details I used the word may because the resulting reflection could be a significant factor or it may have no impact at all under other circumstances or something in between.

Thanks for the info, I thought that microphone positioning would have a strange effect. I have an old Lifecam VX 6000 with the casing removed. It has a small condenser microphone on it. It is so sensitive that it can faintly pick up low voices and sounds from two rooms away through closed doors.

Eavesdropping is a violation of privacy, I hope you're not engaging in this type of behavior....

Someone entering my property/home without my permission has no right to privacy.

People in public places also have no right to privacy.

So the concept of eavesdropping is not an absolute and depends on the circumstances under which it is conducted.

The laws vary from state to state...It is illegal to record the police, even in public in some states...

http://wiki.answers.com/Q/Is_it_illegal_to_record_police

"In Illinois, an eavesdropping device cannot be used to record or overhear a conversation without the consent of all parties to the conversation. 720 Ill. Compiled Stat. Ann. 5/14-1, -2. An eavesdropping device is defined as anything used to hear or record a conversation, even if the conversation is conducted in person. "

Man Faces Life In Jail For Recording Police

No, its not for that. I am just experimenting with electronics.

Carry on, just a heads up....

Yeah, that law is being challenged as I write. I do not think it is constitutional, but Illinois (particularly Chicago) feels free to make up any laws they want regardless of the rights of the people.

That also is an attempt to shut down the press.

Paranoid? No one is more paranoid than the government.

The characteristics, S/N ratio, Freq Response, THD level of mic are fixed by design. These paramenters detemine the quality of its output.

However you connect them, it will not improve these paramenters.

Connecting the mic in series will only increase the output level, both signal and noise, so S/N ratio has no change.

A properly designed mic pick up will have enough gain for 1 mic. So having a higher signal level is not useful unless you have better S/N ratio.

Parallel connection will only lower output resistance of mic. This is also not useful because all input amplifier have very high input impedance.

You would probably be better off to invest in a higher quality microphone and a low noise preamplifier. You will find that, depending on the frequency range you are assessing, there isn't as far to go as you think. I have sat in the basement of a house on the side of a mountain with everything that makes noise in the house shut off at 3 AM and with a linear weighted sound pressure meter the best noise floor I could get was about 45dB. At that point I could detect an airliner flyover and a train several miles away. If you roll off the low end with an "A" weighting filter you can go lower. The world is a lot noisier than most people know. If you ever get a chance to go into a good vibration isolated anechoic chamber, (they have a really nice one at Fr. Rucker in Alabama) you will be amazed by how much more quiet, really quiet is.

If you mount these microphones in a plane, then the array will be more sensitive in a direction perpendicular to the plane, and sounds coming from other directions will tend to cancel. The spacing should be smaller than the wavelength of the highest frequency of interest. The directionality will be greater (narrower beam) for higher frequency sounds. The effect is very similar to using a parabolic reflector.

Or just buy a Big Ear.

It does not have to be an array. You can put the microphone at the centre of a parabolic reflector, which enhances the sensitivity of the microphone considerably

http://www.amazing1.com/accoustics.htm

It will depend on whether the sound you are trying to measure is near or far field. If it is near field, it looks like separate sources and you will have severe phase problems. If it is far field, your idea could work, but couldn't you obtain the increased sensitivity more easily with one microphone and a parabolic reflector?