The SM90 Microphone is designed specifically for surface-mounted applications. It is a professionalquality permanently-biased condenser microphone with a hemispherical pickup pattern (omnidirectional in the hemisphere above the mounting surface.) The SM90 takes advantage of the well-known principle that, at a barrier or boundary, sound pressure doubles compared to its value if the boundary is removed. When placed sufficiently near the boundary surface, a microphone has effectively 6 dB higher sensitivity and approximately 3 dB greater rejection of random background noise. Because of its high sensitivity and extremely flat frequency response, the SM90 can be used for distant pickup in circumstances where close miking would not be practical. The low-frequency cutoff switch in the preamplifier permits using the SM90 even in environments where low-frequency noise (e.g., from fans or air conditioners) would otherwise make distant pickup impossible. And the omnidirectional polar pattern of the SM90 means sound is picked up equally in the full 360° hemisphere around the microphone; there is no off-axis sound coloration or variation. The SM90 can also be used for close pickup of an individual instrument, mounted, for instance, inside the lid of a grand piano or on the floor next to a bass drum. Experimentation and critical listening will demonstrate Copyright 1984, Shure Brothers Inc. 27A2162 (DJ) the best location for any particular purpose or effect desired.