Subtractive microphone designs produce cardioid and dipole patterns via port spacing and delay

Evidence

A simple and widely used design is a firstorder subtractive directional microphone, which can be constructed with a single microphone having two ports or with two separate microphones, one port at each. Such a design makes possible first-order directivity patterns including cardioid, hyper-cardioid, super-cardioid, and dipole patterns, as in Figure 14.5 on page 290. In the one-microphone design, sound is fed to both sides of the microphone diaphragm, and the directivity pattern is controlled by the port spacing and an internal acoustic delay. In the two-microphone construction, the signals of the two microphones are subtracted, and the directivity pattern is controlled by the microphone spacing and an electrical delay between the microphone signals. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 2750

Categorization

• DEFINE: Explains the mechanism behind first-order directional microphones and how cardioid patterns are physically produced.