Choosing a Microphone: Polar Patterns-Directional
November 21, 2005
Microphones with directional characteristics do not have a uniform pickup pattern as do omnidirectional mics. Directional mics are more sensitive to sounds emanating from some directions and less to others.
Two of the types of directional mics are cardioid, and hyper- or super-cardioid. Cardioid mics have a polar pattern that is rather heart-shaped, with maximum response in the front of the mic, minimum response at the rear, and a gradual decrease in response from the front to the rear. Handheld mics for close-in vocals are often cardioid. These mics are useful for rejecting sound from monitor speakers directly in front of the performer (and behind the mic). But often monitor loudspeakers are placed at some angle to the performer, say 60 degrees or so. To accommodate that situation, there are vocal mics available with a super-cardioid pattern. Super-cardioid and the more narrow hyper-cardioid mics have a narrow but strong response on-axis (sound coming in the front of the mic), with the response falling off rapidly off-axis. The minimum response of these types of mics is not at the rear like the cardioid, but rather at some angle off the side. That's why a super-cardioid can work well on stage, rejecting sound from monitor loudspeakers (and other musicians) off the side. The super- or hyper-cardioid mic, unlike the cardioid, has a rear lobe, which means it does pick up sound from the rear. While this response is lower than the on-axis response, it could be significant in some situations. Other examples of hyper- and super- cardioid mics are the long narrow shotgun mics used on booms in sound stages, mounted on ENG cameras, positioned at the side of race tracks or behind home plate, anywhere where the sound source is at some distance from the mic. When aimed carefully at the intended sound source, these mics are great for isolating the on-axis sound from unwanted sounds that are rejected at the sides. But remember that lobe at the rear to avoid picking up an unexpected profanity.
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