Tubular Shield for Enhancing Noise Cancellation of Pressure‐Gradient Microphones

The object of this research was the development of a shield whose noise‐cancellation properties would effectively complement those of a pressure‐gradient microphone, thus providing substantial cancellation at high frequencies where the pressure‐gradient microphone alone has little or no cancellation. In contrast to the normal vented‐cavity type, the new shield is tubular in shape with the microphone and mouthpiece at one (closed) end, and the other end open for breath expulsion. The intended microphone has a cosine directional pattern and is positioned so that its null plane coincides with the tube axis. Therefore, unwanted noise arrives at both sides of the exposed diaphragm in phase, producing no output. Further enhancement of noise cancellation is provided by lining the tube with acoustical absorption along the inner wall. The mouthpiece is located on the side of the tube, directly above the microphone. Thus, speech is effectively received as a result of proximity to the microphone and because of the l...