Boundary Mics and Automatic Mic Mixers
Aug 21, 2012 11:45 AM, By Bob McCarthy
This month’s showcase will feature boundary microphones and automatic mixers. The coupling of these two entities steers us in a decidedly corporate direction, emphasizing conference, podium, courtroom, and boardroom applications. Let’s start at the beginning of the signal path and work our way from mics to mixers.
The principal behind the boundary mic is the same as our reasons for placing a subwoofer on the floor, except in reverse. The idea is to use the reflection constructively to achieve a hemispheric response, which adds 6dB of “free” sound level. In the case of the subwoofer, this is easily achieved since the wavelengths in play are very large. In the case of the boundary mic, the high frequency range is limited by how close we can get to the reflecting surface and still stay within the phase variation required to avoid cancellation. Innovations in transducer technology have brought us closer and closer to the surface, and the modern boundary mic now features a wide variety of patterns and options. Let’s take a closer look at the options available.
If you are looking for an extremely flat boundary mic the AKG MB3 certainly fits the bill. After all, it rises less than half an inch above its mounting surface. The mini-boundary line provides a low-profile solution with supercardioid performance from the company with the longest track record in the field of boundary mics. The MB3 is completely self-contained with the phantom-powered compact electronics mounted inside the tubular assembly. Mounting is accomplished by a single hole drilled in the boundary surface and connection via XLR. An LED on the external grille lights when the mic is hot. Up to four of the MB series mics can optionally be controlled by the MB-100 interface, which provides separate inputs, outputs, and programmable switching connections.
The Astatic/CAD Audio 930VPL may look like a garden-variety mouse mic, but there is much more going on here than meets the eye. First is the fact that the polar pattern is continuously variable via a programmable membrane switch, LED, and logic interface. The polar pattern can be optimized for the particular application or environment. Another feature found in the modern creature is immunity from the RFI intrusions of cell phones and other two-way communication devices. The 930VPL features logic I/O functions that can be used with automatic mixers, teleconferencing systems, and control systems. The logic input can remotely control the LED as well as the membrane-switch activation. The 930VPL is primarily designed for speech and vocal pickup in governmental, institutional, religious, and business applications.
If you are looking for a clean a simple condenser boundary mic solution, be sure to give a close look at Audio-Technica’s ES947. Make it a very close look or you will miss it since it is just over 1in. in diameter and surface-mounted with a very low profile. The 120-degree cardioid patterned, RFI-protected microphone is ready to run, with little more needed beyond a 1in. hole and a boundary to mount it on. The mic is XLR terminated, and its self-contained power module eliminates the need for additional external in-line electronics. The microphone is protected by a rugged all-metal case with a two-layer steel mesh grille and mounted with provided isolators to reduce vibration noise. The unit is capable of input levels up to 142dB SPL, which makes it ideal for a modern-day town hall meeting. It is available in black and white.
If you are looking for a no frills alternative consider the Peavey PSM 3. This is the traditional mouse shape, with a low profile and is available in black or white. It is as comfortable on the stage as it is in the conference room. The phantom-powered PSM 3 uses multiple condenser capsules to create a directional response, which increases the gain before feedback and reduces ambient noise.
If you are looking for a boundary mic that can interface directly with your computer the Samson UB1 USB should be of interest. The UB1 is an omni-directional surface-mount condenser microphone with USB output, compatible with both Mac OS and Windows. The UB1 also ships with Cakewalk Sonar LE digital audio workstation software. The UB1 can be placed on a conference table, podium, altar, or mounted using the keyhole mounting points.
The Shure MX392 and MX393 Microflex wired boundary Microphones are designed for conference table or stage work. The phantom-powered condenser mics are available in cardioid, supercardioid, and omni models. The MX392 comes with an attached cable, while the 393 is connectorized. They are equipped with features like programmable, silent membrane switches, logic inputs and outputs, and green LED indicators.
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