Hardware Hacking 33Chapter 10: A Simple Air Mike
You will need:
- An electret microphone element (see text below.)
- 8’ lightweight shielded cable.
- Some plugs to match the jacks on your amp , recorder or mixer.
- 9 volt battery and battery hook-up clip.
- An amplifier or mixer.
- Assorted resistors and capacitors.
- Packaging supplies as needed.
- Hand tools, soldering iron and electrical tape.
We’ve saved the most normal form of microphone for last: after coils, contact
mikes, and tape heads we finally get around to your basic hear-my-song mike.
From any number of sources (Radio Shack, web retailers, electronic surplus
outlets) one can buy, quite cheaply, high quality “electret condenser
microphone” elements. You can also scrounge them from telephone answering
machines and even some toys. These are the basic building blocks of recording
microphones that can sell for several hundred dollars. All that stands between
your US$2.00 purchase and a pretty good mike is a handful of cheap components
and a soldering iron.
If you have any choice of models when you go to buy an element, look for the
highest signal-to-noise ratio and a flat, extended frequency response. If you have
a choice between “cardioid” (directional) and “omnidirectional” pickup pattern
bear in mind that the omnidirectional models usually have a flatter response
curve -- the quality of the sound tends to make up for its lack of directionality.
Figure 1 shows the basic wiring. A 9 volt battery powers the mike through a
resistor. A capacitor blocks this voltage from entering your amplifier or mixer.
A switch turns the battery on and off -- the microphone drains very little current,
but the switch will help your battery last for months. It’s best to turn on or off
the mike when it is not connected to your recorder or amp, to avoid big thunks.
Solder on whatever plug matches your recorder/mixer -- I’ve included in Figure
2 the rather odd connections needed if you use an XLR connector (used on the
microphone inputs of more professional audio gear.)