Whether you are a nature lover, bird watcher, or secretly hope to be a spy, building your own parabilc microphone is a great project. Using cheap items that can be found in most hardware stores, you can build a working unit in an afternoon.
Parabolic Mic Basics
A parabolic microphone, also called a "Big Ear," is a piece of specialized audio equipment, designed to pick up sound from a distance. It does this by using a reflector dish to collect sound waves, refocusing them into a smaller area, which a microphone can then pick up. These microphones have found extensive use in recording bird calls and nature sounds, and in surveillance and espionage.
Parts of a Parabolic Microphone
There are only a few parts to a working parabolic microphone. A finished unit will have the reflector dish, a microphone, an arm or rod holding the microphone in place, and an output for the microphone. For ease of use, most hobbyists will also attach a handle or tripod mount.
Find a Suitable Parabolic Dish
While an ideal reflector dish will conform to a standard parabolic shape, many hobbyists and tinkerers have found success with reflectors that are not true parabolas. In practice, though a parabolic shape will produce the best sound quality, almost any dish like reflector will work. Various projects have used umbrellas, wok lids, salad bowls, barbeque lids, and even round disk sleds. High quality, premade parabolic reflectors can also be ordered through several online retailers.
Find the Focal Point
The parabolic microphone works by reflecting sound waves from a larger area (the reflector dish) into a smaller area (the microphone). In order to make your parabolic microphone work, you need to find this focal point.
The simplest method is to place the microphone in the center of the dish. Point the dish towards a distant audio source, and adjust the distance of the microphone, keeping it centered. Wherever the volume is best and the sound quality clearest should be the focal point. When you attach the arm, if you haven't already, it will hold the microphone in this position.
Attach the Arm, Microphone and Handle
Once the focal point has been found, attach and position the microphone arm. This arm may be a rod extending from the center of the dish, or a bent wire connecting from the outside lip of the dish. The placement of the arm itself is not hugely important, but be careful to use an arm that is not likely to disturb or absorb sound. Coat hanger wires and metal rods work great, because they are relatively easy to adjust and don't disrupt sound too much.
To the end of this arm, at the focal point that was determined earlier, attach a microphone. Clip on lapel mics over a simple way to attach and adjust the positioning, but may be underpowered for some uses. While hobbyists have used a wide variety of microphone types, the ideal microphone is a highly sensitive omnidirectional microphone.
On the backside of the dish, you may also wish to attach a handle or tripod mount to the assembly. If you will be using the dish for long periods of time, a tripod mount may be the best option.
Connect to an Amplifier or Recorder
In order to use your new parabolic microphone, you will need to connect your microphone to either an amplifier or recorder. Pocket sized amplifiers that connect with a mini headphone jack are sold through most major electronics retailers. Whether you plan to listen or record, amplification will allow you to get more sound out of your equipment.
If you choose to record audio, here are also a number of options. Cassette tape recorders will work, as will newer digital voice recorders. Make sure to find a recorder that offers input from an auxiliary source. It is also important to find a unit that allows you to connect headphones to listen as you record, or you won't be able to hear anything until after the fact.