Parabolic microphone

Parabolic microphones are generally not used for high-fidelity applications because dishes small enough to be portable have poor low-frequency response.

This is because, from the Rayleigh criterion, parabolic dishes can only focus waves with a wavelength much smaller than the diameter of their aperture.

The wavelength of sound waves at the low end of human hearing (20 Hz) is about 17 metres (56 ft); focusing them would require a dish much larger than this.

A typical parabolic microphone dish with a diameter of one metre has little directivity for sound waves longer than 30 cm, corresponding to frequencies below 1 kHz.

This application is supported by a study comparing parabolic microphones to unaided hearing in detecting and comprehending calling subjects at distances out to 2500 meters.

Parabolic microphone used at an American college football game.
A Sony parabolic reflector, without a microphone. The microphone would face the reflector surface and sound captured by the reflector would bounce towards the microphone.