Technology Showcase: Boundary Microphones
Apr 9, 2009 12:00 PM, By Bennett Liles
From conference rooms to stage performances, the applications for boundary microphones are numerous.
With a half-cardioid pickup pattern, the Peavey PSM 3 back-electret condenser boundary mic can be used in sound reinforcement, teleconferencing, and recording with a frequency response of 50Hz to 20kHz when used on an infinite boundary. The output level is -35dB at 500V, and the supplied 10ft. cable has a TA3F at the mic end and a standard XLR on the other. The maximum SPL handling figure is 130dB and the dynamic range is 106dB. The unit is powered by a 9V-to-52V power supply and draws only 5mA. The microphone has a sensitivity of -35dBV/Pa and a rated impedance of 50Ω.
For classroom use, the Revolabs TableTop wireless boundary microphone can be ordered as the omnidirectional or the unidirectional. Both are the same size and weight and operate in the frequency range of 1.92GHz to 1.93GHz. This provides a transmission range of 65ft. to 100ft., and there is an out-of-range alarm when the RF signal begins to drop out. The lithium-polymer battery provides up to 8 hours of operation time on a full charge, and the mic provides a 100Hz to 6.8kHz audio frequency response with 128-bit encryption for a secure wireless link.
The CM11B omnidirectional condenser boundary microphone from Samson can be mounted on tabletops or walls, and all the electronics are mounted in the mic body rather than requiring an external electronics pack. The unit operates on phantom power at 9VDC to 52VDC, and it incorporates a heavy neoprene rubber pad to decouple the mic body from the wall or table on which it is mounted. The mic body accepts a mini XLR connector and the other end of the 30ft. cable provided with the mic has a standard XLR connector. The unit has a 30Hz-to-18kHz frequency response and a maximum SPL rating of 127dB.
Available in gray or beige, the CUB-01 miniature boundary microphone from Sanken is less than 1 1/2in. in diameter, and it uses a unique square-shaped cardioid capsule to significantly enlarge the area of the diaphragm and provide a flat frequency response down to 70Hz. The microphone can handle a maximum SPL up to 122dB and operates on 44VDC to 52VDC phantom power. The output impedance at 1kHz is 180Ω and the A-weighted equivalent noise level is less than 16dB. A variety of accessories are provided including a rubber base, windscreen, instruction manual, and vinyl case.
The BLM 03 Cg miniature boundary-layer microphone from Schoeps has an active cable hard-wired to it that allows the mic to be connected to any amplifier in the Colette series except for the battery-operated CMBI model. The BLM 03 Cg has all the features of the BLM 3g in a smaller size. The frequency range is 20Hz to 20kHz with a sensitivity of 19mV/Pa and an A-weighted equivalent noise level of 12dB. The mic can handle a maximum SPL of 128dB.
Designed especially for speech pickup, the 912 S pre-polarized condenser half-cardioid microphone from Sennheiser has an integrated membrane switch that is programmable for either on/off, push-to-talk, push-to-mute, or always-on modes. The frequency response can be tailored with DIP switches for low cut, low and high boost, low boost, and linear. The frequency response is 20Hz to 20kHz, and the mic uses 48VDC phantom power.
The MX396 Microflex multi-element boundary microphone from Shure comes in two- or three-element configurations: the MX396C/Dual with 0-180-degree pickup and the MX396C/Tri with 90-0-90-degree pickup. The mic has a frequency response of 50Hz to 17kHz and a maximum SPL of 122dB. There are individual outputs for each element, and a programmable mute switch offers several modes of operation. Included in the design are a bicolor status indicator and a logic output for remote LED and mute control.
The MCBM-300 back electret condenser microphone from Speco Technologies is designed for table placement, and it includes a 20ft. cable with a standard XLR male on one end and a mini-XLR at the mic end. With its stealth design, the mic has a unidirectional pattern and provides a 60Hz-to-16kHz frequency response. With a 250Ω impedance, the unit exhibits a sensitivity of -36dB ±3dB, includes a mute feature, and operates on 9VDC to 52VDC phantom power.
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