Microphone and Pre-amplifier question

How about you explain what this project is in aid of ?

Graham

I think the caps select an attenuation on the output of the capacitive transducer.. I have some Shure SM81s that inset a 10pf cap in series for 10dB attenuation. This is BEFORE the mic preamp, so it effectively attenuates the mic output... useful when recording live artillery fire demonstrations, for example.

I have this chip ISD1110S (Windbond Voice Recorder) from an old project. I want to utilize it into some useless, novelty gadget. I had an idea of creating a small recording device that picks up, from about

30ft away, any sound that surpasses a certain sound pressure level. I was thinking maybe 20 dB SPL.

The device will be used to prank my friends while, say, they are using the toilet. The device would emit a loud shriek and then record my friends' reaction on the voice recorder. If I put it at least 30ft away, then I can mount it on top of the ceiling so they won't be able to get it down right away to destroy it.

You're going to have more than a little trouble doing that with a cheap electret capsule for sure ! Chances are that the capsule itself has an equivalent noise of > 20dB SPL.

I'm not clear why you want to use the Maxim part either. Was it simply a part you came across by chance ?

LOL !

Graham

electret

Yeah, I figured I'd use some "ready-made" pre-amp IC. That was one of the things that showed up while searching for samples on Maxim's site.

What kind of microphone and pre-amp do you suggest?

The mic data sheet says that it has a minimum SNR of 60dB at f=1kHz with 1 Pa sound pressure.

electret

noise

You could use any old (not too noisy) op-amp of your choice. The electret capsule already has the jfet buffer in it.

Your biggest problem at 30 feet is going to be localising the sound source. For that you need high directional sensitivity and the way to do that seems to be the 'shotgun microphone' that does clever acoustic things to achieve the result. I wonder if you could build your own ?

Well... 0dB SPL is 20 uPa which makes 1Pa = 94dB SPL.

So the mic's equivalent noise is ~ 34dB SPL. Not too surprising. Typical of the genre I expect.

Graham

For that

'shotgun

if you

Shucks. I thought this project was as simple as using an electret mic. I guess not. I haven't looked into shotgun microphones, yet. However, when my dad was shopping one for his camera, it was worth about $80 and looked pretty bulky.

I wonder what kind of mic my bluetooth headset uses. Every time I use it in an area with a higher background noise level, the people on the other line complain that they can hear the background.

the genre

Hmm.. so this mic is not suitable for any sounds below 34 dB SPL. I guess there's so much about microphones that I didn't take into account .... and need to learn. I guess 34 dB SPL is workable for my needs because the SPL for a quiet room is supposed to be around 40 dB. I guess as long as the device triggers with the sound of water flowing then that should be good enough.

For that

'shotgun

if you

I'm sure it'll be similar to the other one. You might be surprised how loud 'background noise' can be.

I nearly forgot the parabolic reflector. Somewhat large but has the advantage that it also amplifies the SPL at the mic.

Graham

'background

that it also

mic.http://www.bio.umass.edu/biology/kunkel/gjk/microphone.htmhttp://www.canford.co.uk/blueprintonline/blueprintaug2003/bigears.aspx

Parabolic reflectors, huh. Cool. I'll read up on it. I don't know much about mics. I thought it was as simple as hooking them up into an opamp and so on.

electret

noise

part

capsule

For that

'shotgun

if you

Of course - here's just one:

Cheers! Rich

For that

'shotgun

if you

the genre

Admit it - you just want sound for your toilet-cam, right? ;-)

Cheers! Rich

For that

the 'shotgun

wonder if you

the genre

Doesn't everyone have quadraphonic toilet sounds?

Haha. Not my cup of tea. Really, I think it'd be interesting to come up with some device like this because it's fun and that other kids will want to learn how to build it.

There are still kids who want to learn how to build things ???? !!!!

Slightly not fair since I know my nephew does. When he gives me the rail currents for the various voltages I'll be posting about it in s.e.d

Graham

That's the problem. The interest is not there. So I figured if we show them something fun, then they'll be interested in learning some more. In my local IEEE student branch, we do an expo show for elementary kids every semester. But the kids are really not interested in just seeing a basic inverting configuration op-amp circuit laid out on a breadboard and its output connected to the oscilloscope.

That's also the main reason why I try to learn more about electronics by asking a bunch of dumb questions because eventually, I'll be able to understand it better and in turn explain it better.

Sounds good.

There's no such thing as a dumb question (well as long as you did *some* homework). If only more ppl asked things instead of making often erroneous assumptions, usually because they're scared to ask !

Graham

'background

that it also

mic.http://www.bio.umass.edu/biology/kunkel/gjk/microphone.htmhttp://www.canford.co.uk/blueprintonline/blueprintaug2003/bigears.aspx

A parabolic reflector will limit the frequency response depending on the size. Since the wavelengths of the sounds we can hear are pretty large using a small diameter reflector will filter out low frequency sounds. I wonder what frequency range most farts are in? Maybe you can use a small parabolic dish to find out how tight your friends are. ERS

For long distance work this tends to be a beneficial side effect. Much unwanted background noise is LF.

Graham