Weekend Project: Parabolic Microphone

Here's a an easy to make, dollar store DIY spy microphone that lets you listen from afar and bring the sounds up close. Credit for the original project goes to Jim Lee. From Make Magazine Volume 14.

Parabolic microphone - Wikipedia, the free encyclopedia

A parabolic microphone is a microphone that uses a parabolic reflector to collect and focus sound waves onto a receiver, in much the same way that a parabolic antenna (e.g., satellite dish) does with radio waves. Typical uses of this microphone, which has unusually focused front sensitivity and can pick up sounds from many meters away, include nature recording, field audio for sports broadcasting, eavesdropping, law enforcement, and even espionage.

Parabolic microphones are generally not used for standard recording applications because they tend to have poor low-frequency response as a side effect of their design. This is a direct result of the physical laws that govern sound waves.

Parabolas only focus waves with a wavelength much smaller than the diameter of the parabola. Since sound waves travel at 342 m/s through the air (speed of sound), obtaining hi-fidelity sound (down to 20 Hz, the lower limit of human hearing) would require a parabola with a diameter greater than 17 meters (= 342 m/s / 20 Hz). Most parabolic microphones sacrifice low-end fidelity to get a more manageable size.