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.
One of the tiniest entries in the boundary microphone arena is the MB-1 from Crown International. Once the unit is mounted onto a tabletop, the protruding area is barely bigger than a quarter, and there is a bottom-mounted 1/4in. phone plug for the audio connection. This plugs into a matching female connector provided in an insert mounted beneath the table. When not needed, the mic can be removed and the mounting hole is filled with a disk supplied with the microphone. The MB-1 must be used with the MB-100 interface, which powers up to four of the mics, provides switching connections, and offers balanced outputs from the interface.
The BLM4060 prepolarized omnidirectional miniature condenser microphone from DPA Microphones has a 5.4mm vertical diaphragm and a rubber disk that holds the microphone element. The unit exhibits a wide frequency response of 20Hz to 14kHz with a 7dB soft boost at 8kHz. Nominal sensitivity is -34dB ±3dB with a signal-to-noise ratio of 71dB at 1kHz and total harmonic distortion is less than 1 percent up to 123dB SPL level. Maximum SPL before clipping is 134dB, and the output impedance is 30Ω to 40Ω. The BLM4060 is powered with a DPA power adapter supplying 5V to 50V.
The Electro-Voice RE90B offers a half-cardioid pickup pattern with a back electret condenser element. The frequency response is 80Hz to 15kHz ±3dB with an output impedance of 200Ω and a maximum SPL level of 130dB with 1 percent total harmonic distortion at 1kHz. The unit operates on 9VDC to 52VDC, and it has a cable that is attached at the microphone end on an internal terminal block with an XLR connector attached at the other end. The RE90B uses about 2.5mA of current, and it has an integrated pop filter for working close to the microphone.
Designed not only for conferences but also for stage-production pickup and live music, the CBM1 omnidirectional electret condenser from Gold Line has an exceptionally high 150dB maximum SPL. It is one of the few boundary micro¬phones to incorporate a full-size XLR connector on the mic case, allowing direct connection of standard audio cable. The wide dynamic range of 28dB to 121dB also aids live-music pickup. There is an on/off switch beside the audio connector, along with a second switch for 6dB bass boost and cut to custom-tailor the response. The overall frequency response of the unit is 20Hz to 20kHz, and it operates on 12VDC to 48VDC.
The CM-602 unidirectional condenser boundary microphone from JTS Professional is intended for conference, house-of-worship, and theater applications. The CM-602 has a red LED indicator and a large membrane on/off switch right on the front of the mic body. The output connector is a mini XLR male with a standard male XLR at the other end of the supplied cable. The unit has a frequency response of 30Hz to 12kHz, a sensitivity of -53dB ±3dB and a signal-to-noise ratio of 67dB.
The MP-30 pressure-zone microphone from Milab Microphones is designed for sound pickup in applications from pianos to conference rooms, with a frequency response of 40Hz to 20kHz and a maximum SPL handling of 110dB. The microphone has an A-weighted noise level of 24dB with 1mA current draw and an output impedance of less than 200Ω. The unit operates on a 12VDC-to-52VDC power supply and comes with a 6ft. cable.
The CBM 40X cardioid boundary microphone from Nady has an electret- condenser element powered from an external 9V-to-52V power supply and is packed in a heavy duty die-cast case with a rubber pad on the bottom for minimizing mechanical rumble and vibration. To maintain the small cross-section, the audio connector is a mini XLR. The supplied cable has the mini XLR on one end and a standard XLR connector at the other. The total frequency response is 50Hz to 18kHz with a maximum SPL capacity of 130dB and an impedance of 250Ω. The CBM 40X is intended for sound reinforcement, professional recording, and conferences.
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