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.
For applications requiring a small, movable boundary mic, Audix offers the ADX60 prepolarized boundary condenser microphone with hemi-cardioid pickup pattern. The mic operates on 9VDC to 52VDC phantom power, provides a frequency response from 50Hz to 18kHz, and comes with a 25ft. cable and phantom power adapter (APS-910). The housing is precision die-cast zinc with a 12mm capsule, black e-coat finish, and steel mesh grille. The audio connection is mini XLR, and the APS-911 battery-operated phantom-power adapter has an on/off switch and bass roll-off. The mic has a signal-to-noise ratio of 65dB and a 250Ω output impedance.
One of the BM series contractor microphones from Avlex, the BM91BJ is intended for tele¬conferencing, distance learning, courtrooms, and meeting chambers. The mic is customizable with interchangeable cartridges of cardioid, supercardioid, and omnidirectional elements available. The design includes a bottom mounted 1/4in. TRS connector for quick placement and removal. The frequency response is 30Hz to 20kHz with a signal-to-noise ratio of 65dB, a maximum SPL capacity of 135dB, and a sensitivity figure of -65dB ±3dB. The case is paintable, and a custom paint mask is included with each microphone.
Bartlett Microphones has just introduced its TM-125 stage floor microphone for theatrical pickup using the boundary-layer principle. The unit can also be used on boardroom conference tables. Using a miniature condenser mic capsule with an asymmetrical placement that reduces standing wave pickup, the TM-125 features a thick steel housing that can withstand being stepped by stage performers. The supercardioid polar pattern directs sound pickup toward performers onstage and away from the audience and orchestra. The frequency response is 60Hz to 18kHz with a signal-to-noise ratio of 94dB at 94dB SPL. The unit produces 3 percent THD at an SPL of 120dB.
The MPC 22 acoustical boundary microphone from beyerdynamic is a permanent flush-mount design for tabletops and ceilings. Condenser mics with a half-cardioid polar pattern typically work well for these applications, and the elastic bearing rings on the mounting shaft help provide mechanical isolation of the mic from vibrations in the mounting surface. The MPC 22 offers a frequency response of 50Hz to 20kHz, a maximum SPL of 124dB at 1kHz, and an A-weighted signal-to-noise ratio of 26dB. The unit operates on 8VDC to 52VDC phantom power, and it connects with a 3-pin XLR at 200Ω output impedance.
For meeting rooms, conferences, and stage productions, Bogen offers the SCU250a cardioid condenser boundary mic that operates on a phantom power supply of 9VDC to 52VDC. The heavy-duty metal case is isolated to provide insulation from surface vibration, and there are mounting keyways for secure attachment to the mounting surface. The mic provides a frequency response of 20Hz to 18kHz and a sensitivity of -58dB ±3dB, and it comes with a 26ft. quad cable terminated in a male XLR connector. The signal-to-noise ratio is more than 65dB with an output impedance of 250Ω.
Clockaudio markets the C002E omnidirectional condenser microphone for mounting on walls, floors, pianos, and a variety of other flat surfaces in a very low-profile, un¬obtrusive form. Finished in stone gray Nextel, the mic comes with a 24.5ft. cable terminated with an XLR connector. The unit operates on 9VDC to 48VDC phantom power and delivers a frequency response of 30Hz to 20kHz. It has a maximum SPL handling of 120dB with 1 percent total harmonic distortion and provides an A-weighted signal-to-noise ratio of 68dB. The sensitivity is -47dB ±3dB at 1kHz, and there is a switchable bass filter offering -4dB per octave at 400Hz to -6dB per octave at 100Hz.
The C200 series boundary microphones from Communication Technology are a semi-cardioid electret condenser model with phantom powering from 24VDC to 48VDC, and is available with or without on/off switching. The case is isolated from mechanical shock and vibration by a soft neoprene molding. It comes with a 14.7ft. cable terminated in an XLR connector and an output impedance of 600Ω. The mic exhibits a sensitivity of -35dB ±3dB at a frequency of 1kHz and the maximum SPL rating is 130dB. The frequency response is 50Hz to 18kHz, and the C200 is available with or without an on/off switch.
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