Parabolic microphone
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A parabolic microphone uses a parabolic reflector to collect and focus sound waves onto a microphone 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, 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 than the diameter of the parabola. Since sound waves travel at 300 m/s through the air (speed of sound), to get hi-fidelity sound (down to 20 Hz, the lower limit of human hearing) would require a parabola with a diameter greater than 300 m/s / 20 Hz = 15 meters in diameter. Most parabolic microphones sacrifice fidelity to get a more manageable size.
See also: Microphone