Things You'll Need
- Aluminum tubing, 3/8 inches diameter and 56 feet long
- Crystal microphone cartridge, such as Lafayette PA-27
- Aluminum stripping
- Camera tripod
- Screws and nuts
- Rubber grommet
- Microphone cable
Shotgun microphones are the most highly directional types of microphones. This means that they have an extremely low sensitivity to sounds occurring behind or to the sides, but an extremely high sensitivity to sounds occurring in front. For this reason, shotgun microphones are excellent at detecting sounds far in the distance, and are frequently used to record wildlife and sporting events.
Decide what frequencies of sound you want to hear. A simple shotgun microphone with only a few tubes will be able to pick up only a limited frequency range of sounds. If you want to produce a higher fidelity recording with your shotgun mic, you’ll need to use most or all of the 56 feet of tubing you’ve acquired.
Do some calculations to determine the lengths of the aluminum tubes you’ll have to cut. Aluminum tubes resonate at particular frequencies to pick up sounds. Dividing the speed of sound (1,100 feet per second) by a given frequency will determine the wavelength. The length of a given aluminum tube will be half of the wavelength.
Cut the tubes to varying lengths based on the calculated wavelengths. You can do this with a hacksaw. Tubes should range in length from 1 inch to 36 inches, graduating in steps of 1 inch. A 37th tube can be added for symmetry. Cut the aluminum stripping into support brackets to attach the tubing bundle to the tripod.
Glue the tubes together using rubber cement or epoxy glue in a bundled fashion. The longest tube should be placed in the center of the bundle, with subsequently shorter tubes arranged in a circular fashion around the center tube. If done correctly, the tubes on the outside of the bundle should range in length from 1 inch to 17 inches.
Assemble the microphone-funnel structure. This consists of a microphone cartridge mounted inside of a funnel, with a cable running out of the narrow end of the funnel, secured with a rubber grommet. The larger end of the funnel can then be fixed to the bundle of aluminum tubes. Connect the microphone cable to an input recording device.
Try applying a high-gain amplifier to your design to assist in picking up distant sounds.
Be aware that your shotgun mic is extremely directional. Your microphone may appear to be nonfunctional if you’re aiming the unit even slightly to the side of your target sound source.