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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 metres away, include nature recording, field audio for sports broadcasting, eavesdropping (for example, espionage), and law enforcement.
Parabolic microphones are generally not used for high fidelity recording applications because dishes small enough to be portable have poor low frequency (bass) 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 feet); focusing them would require a dish much larger than this. A typical parabolic microphone dish with a diameter of one metre would have little directivity for sound waves longer than 30 cm, corresponding to frequencies below 1 kHz.
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