Sensitive mic questions: electret condenser

[Ventura]

Well, I finally put together a nice 3-transistor, 12-volt dynamic mic preamp for the audio portion of my home security DVR system I’ve mentioned here in the past. (Circuit by Andy Collinson: Circuit Exchange International website.) It works but, as predicted by someone here, my dynamic mic really isn’t right for the job. It’s fine if the sound source is close to the mic, but I need to clearly record a guy who occasionally walks by my home shooting his mouth off at me from about 20—30 feet away, or revving his Honda Gold Wing motorcycle engine. A test recording plays back like the mic is wrapped in a towel. I get a little bit of low end and almost no mid range or higher. This is not going to fly. I need something much more sensitive.

I’m prepared to build a preamp suited to a condenser mic. I could spend the money for a nice Shure mic, but the most sensitive ones are quite expensive and require 48 VDC “phantom power.” I’m wondering if, instead, I can buy a little electret condenser mic element and put something together. Problem is, I have doubts about the cheap ones sold at places like Radio Shack.
1) Do you know of someone selling good quality, sensitive mic elements for project builders?
2) Is it possible to gang together multiple cheap electrets to “pump up” the weak signal? I can see a bundle of, say, four of them. Would it take a mixer, or could they simply be wired together somehow?

Thanks

 

[Nigel Goodwin]

Use a little electret mike, far better than any expensive 'PA' or recording type mikes for what you want.

I would also suggest an opamp preamp, rather than a transistor one.

Expensive condenser mikes are for studio recording, and probably completely useless for what you want.

 

[audioguru]

RadioShack sells "seconds" and "sweepings from a manufacturer's floor".
Digikey sell many electret mics.

If you have a group of mics then they are very sensitive on-axis but have lobing at various frequencies off axis. Some frequencies add and others cancel. You don't want that.

 

[CheapSlider]

Have you considered making your existing mic directional ?

A baffle can shield unwanted sounds from the back while a parabola can give sharp directionality - it may need to be directed towards the source of the wanted sound/

An solid satelte dish works very well - mount the microphone in place of the LNB

Try anything that has a dome or paraboloid shape: dustbin lid, wok, salad bowl, car hub cap, headlight reflector

 

[Ventura]

Thanks for the replies, guys. As I said, I did come to the conclusion that an electret mic element is the way to go in this application. I'm just a bit concerned that a cheap Radio Shack unit might or might not do the job. I'm guessing that for just a few dollars more, I can probably buy a fairly nice, sensitive one. That's why I was wondering if you guys know of a source that dispenses some basic info about the electrets they sell, like the sensitivity rating. I should have thought of DigiKey. I will check it out.
I agree, the parabolic reflector thing would be interesting to experiment with, but I need to keep this installation kind of low profile. I have to be careful that I don't come across to the neighbors looking like I'm setting up a military surveillance listening post. A small, sensitive mic on-or in-my exterior wall should do the job.

Thanks again

 

[audioguru]

Don't buy an expensive poor quality Chinese mic from RadioShack.
Instead, buy a good quality name-brand mic from Digikey.

I have a very expensive Audio Technica mic and a "free" mic from a broken cell phone. They both sound exactly the same.