Directional Microphone ? Shot gun mic ?

[darkm4n]

Hi ,

Everyone here know a good howto / schematic for a directional mic , spy mic , high distance , low noise .. ?

I need to have a range of 30 m minimum ...

Thank's eveyone ! Mihai .

[Da5id4Vz]

IR cameras, hypercardiod microphones...
Hmmm, must be getting pestered by the neighborhood kids.

Try doing some Google searches for parabolic microphone reflectors. Shotgun microphones work on the principle of something called an interference tube to generate a hypercardioid pickup pattern. The bigger (longer) the tube, the more directional the pattern will be.

I think that a parabolic pickup would be relatively easy to make if you can find a cheap source for a reflector, it'll need to be kind of large to get the kind of distance your looking for. The mic capsule needs to be placed at the focus facing the reflector. The depth of the parabola will affect the beam width, the radius of the reflector will affect the gain adjusting the position of the capsule at the focus may give you small variations in the beam pattern.

Both these techniques work good for narrowing the pickup of the microphone and adding some acoustic gain. You will likely still need a lot of gain from your mic preamp. Using a parametric EQ will also help to remove wind noise, and rolling off everything except 500-2500 Hz where most of the voice will be found. A peak limiter and compressor will help prevent overload and blowing your eardrums out when a dog walks up next to the thing and starts barking.

Sorry things haven’t worked out better with the IR camera thing. Did you check to see if the camera has an IR filter that can be removed? That might help with the sensitivity.

I'm afraid that I cant be too much help in the details of getting the job done for you. I only seem to be able to provide help with finding the right direction.

Assuming that your interest in this stuff are mostly parochial, Id recommend to movies to rent, “Blow Out”, Directed by Brian DePalma , and “The conversation” by Francis Ford Coppola. Both are somewhat cautionary things about bad things happening to DIY audio types.

-Dave

[tschrama]

Hi,

I have good experience with the sennheiser ME67 + assecoires. I does need a good preamp. A AD797 could be the basis of a low noise preamp. Rod Elliot also has a good low noise design. A cheap parabollic mirror can be found for about 50$ if you search the net.

Goodluck,
Thijs

[darkm4n]

Yes ... WIth the ir cammera i think it has an filter .. that i have to remove .. but how it looks ? where it is placed ??

About the mic .. a good preamp schematic ? maybe ?

Thanks very much , Mihai .

[tschrama]

Mic preamp schematic..


look at www.sound.au.com and various examples in opamp datasheets.

g,
Thijs

[Da5id4Vz]

These guys make some very large parabolic systems used for broadcasting sport events:

http://www.parabs.com/

The IR filter wont look like much. It will just be a layer of plastic or glass somewhere between the lens and sensor.

[moamps]

Hi,

in Elektor 10/97 was published article "directional microphone..", two electret mics, OP413 preamp, without parabola. Looks very simple and useful. I can send to you this article via mail. (send me your mail address)

regards

[JOE DIRT®]

oh boy you guys are starting to talk about things I played with along time ago...I did successfully design a parabolic mic using a condenser and a 741 opamp as a preamp......I had a wok lid which turned out to be a perfect pickup...I think it was pantyhose that I used for a windscreen

[darkm4n]

If someone can share me here a good design of a parabolic , shotgun microphone it will be great ..

JOE DIRT® if you could help ...

I'am interested in a good design that can pick up sound at 50 m away .. voices ..

Thank's

Mihai .
My email : dark_m4n@Yahoo.com

[pinkmouse]

If you just want to have a play around with directional mics, then you could always just try taping a cheap capsule mic to the handle of an umbrella. Face it towards the fabric, (i.e. not towards the subject), and just slide it down the handle until you get the greatest signal. You might be suprised how well it works, especially for voice.