Audio - How it works

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. Sound entering the parabolic dish from the front axis is reflected into a sphere around the "focus" of the dish, where the microphone element is located. The higher the frequency of the sound, the smaller the size of this sphere. Thus, high frequency sounds tend to be more concentrated onto the pickup element, while low-frequency sounds are "diluted" across a larger volume of space.

Source:
Wikipedia. "Parabolic Microphone." Math Daily. 19 Aug. 2006. 24 Aug. 2006 . .

Shotgun mics are worthy of a complete article to themselves. Usually fairly long, they have an extreme directional pattern, and typically only pick up sound from the general vicinity directly in front of the mic. There are several ways to make shotgun microphones - techniques include a long 'barrel' with slots designed to create an interference pattern that rejects sound from the side, and multi-element designs with phase and amplitude balance between elements. An old method was to use multiple thin tubes of differing lengths, arranged so that the longest tube is in the centre, with smaller tubes surrounding it.

Some shotgun mics use a combination of methods, as well as careful attention to the mic capsule's rear chamber. These mics are useful for location sound recording (for movies or TV), nature recordings, and anywhere else where very high discrimination is needed.

Source:
Rod Elliott. "Sub-Types of Microphones." The Audio Pages. 10 Jan. 2006. 27 Oct. 2006. .