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Tech Showcase: Automixers and Boundary Microphones

For hands-off operation and simple setup, boundary microphones and automatic mic mixers work wonders in keeping things simple and easy.

For hands-off operation and simple setup, boundary microphones and automatic mic mixers work wonders in keeping things simple and easy. Ever since Dan Dugan’s pioneering efforts in automatic microphone mixing, sound operators have sought just the right level of automation. TV audio engineers trying to mix free-form discussion with half a dozen or more participants in a studio with live sound reinforcement certainly welcomed the technology. Boundary mics have brought good sound pickup to the conference room while remaining nearly unseen. The latest models of these great innovations are presented here.


The new CBL31 WLS boundary mic from the AKG DAM series is made for professional conference table applications and wireless operation through selectable pocket transmitters that fit into the housing. The mic body is heavy enough to stay in place, and it incorporates shock-absorbing construction to minimize mechanical noise. Its 120-degree polar pattern allows users to move comfortably without sounding off axis, and the mute switch controls the output while an LED bar indicator shows when it is active. More mics can be cascaded using the 3.5mm connector.

AKG also offers the DMM12 BC reference digital automatic microphone mixer, a 12-channel system capable of handling fairly large conferences and meetings with its ability to cascade up to 10 mics. Versatility is also extended by its two additional stereo audio outputs and one stereo AES EBU output. On the input side, it offers DSP functions such as filters, compressor/limiter, ducking, and routing. Each of its 12 input channels is individually routable to any of the unit’s outputs. Among other adjustable functions are level, treble, bass, low-cut, limiter, compressor, automix yes/no, priority (ducking), pan/balance, and delay. All of this functionality is contained in a single rack space.

Audio-Technica U891RCx

Audio-Technica configured the U891RCx boundary mic with contact closure ability to enable control of an external device in addition to its three-mode activation switch. Users can configure the switch for touch-on/touch-off, press-to-talk, or press-to-mute. Ambient noise and table thumps are minimized by the mic’s built-in 80Hz, 18dBper- octave low-cut filter, and its red LED status indicator can be controlled remotely. The pickup element is interchangeable for cardioid, hypercardioid, and omnidirectional polar patterns. For placement versatility, the rotating PivotPoint connector adjusts the cable exit point. The microphone and all its functions operate from a phantom power supply of 11-52VDC. Its heavy die-cast case and UniGuard RFI shielding reject radio frequency interference.

Audio-Technica AT-DMM828 SmartMixer

In the automixing realm, Audio-Technica also offers the AT-DMM828 SmartMixer 8-channel digital matrix mixer with eight line/mic balanced inputs, individually selectable phantom power, gain attenuation, and low-cut filters along with RS-232 and USB ports for connection to a PC running SmartMixer software. Compatible with Crestron and AMX controllers, the ATDMM828 can activate external devices and exhibit VCA control. Up to 16 mixers can be linked to provide up to 128 input channels, and its settings include NOMA (Number of Open Mic Attenuated), selectable last mic on, and a range of customization adjustments made through the SmartMixer software. The mixer has eight balanced audio outputs. It all mounts in a single rack space.

Audix M60

The M60 miniaturized boundary condenser microphone from Audix has a shock-absorbent bottom layer and mounting holes that allow it to be bolted into a permanent position. The 25ft. shielded cable can pass through the housing at 90 degrees or 180 degrees and can be terminated with a Phoenix or XLRm connector. The durable brass case provides shielding from RFI sources, and the microphone operates on 18V to 52V phantom power. Available in black, satin nickel, or white finish, the M60 has a cardioid pickup pattern (hemi-cardioid when placed on a table). All of the electronics are installed inside the case, so there are no special power adapters or connectors necessary.

beyerdynamic MPR 210 and MPR 211

beyerdynamic’s Revoluto line of desktop microphones have been developed for boardrooms, courtrooms, lecterns, and conferences to be unobtrusive but effective in clear speech pickup. Available in a range of finishes to blend with room décor, the MPR 210 and MPR 211 are based on a patented microphone array technology with the microphone capsules arranged in series, resulting in a long voice pickup range that doesn’t require the presenter to talk directly toward the microphone. The mic button on the MPR 211B can be programmed to operate in several different modes and to use an external control contact. The MPR 211 has an LED strip to display the ready-to-speak status.

Also from beyerdynamic, the BM series boundary layer microphones are only 1/3in. tall and 1in. in diameter with thick metal and welded construction to stand up to classroom environments. Available in black, white, and brushed aluminum finish, these mics also come in models with directional, omnidirectional, and directional pattern with low-frequency roll-off. A very interesting accessory is the new BMR ring containing red, blue, and green LEDs, offering a variety of color combinations and indication codes. The BMR is operated through a media control system or the logic output of a DSP mixer. The BMR consists of the light conductor and a housing for the printed circuit board.

CAD Audio Astatic 210

For security, ambient monitoring, and observation, CAD Audio offers the Astatic 210, a miniature boundary microphone with an allmetal body designed for fixed installation in walls, ceilings, and other solid, flat surfaces. Equipped with a 3.5mm terminal block connector, the mic can be powered on 8V to 18V DC, and its rubber isolation bushing dampens mechanical shock and vibration. This model exhibits a frequency response of 120Hz to 18kHz with an impedance of 50Ω and a maximum SPL of 100dB. The output level is variable from -50dBv to -10.5dBv.

Clockaudio MR 88

Automixing keeps getting more sophisticated behind the scenes while the setup and operation get progressively easier. A case in point is the Clockaudio MR 88 8-channel digital automixing unit with DSP. Housed in a single rack space with a front-panel LCD display, the MR 88 can be configured with a PC through its RS-232 terminal. There are record outputs for each of the eight XLR mic/line input channels, an output level LCD meter, multi-level channel priority system, adjustable off attenuation on each input, NOMA on/ off, and daisy-chain capability for larger microphone setups. There is also 12dB cut/boost on 200Hz and 5kHz for each input channel along with an adjustable limiter.

Clockaudio CRM 202S-RF

Also from Clockaudio is the CRM 202S-RF dualelement boundary microphone for permanent installation with a halfcardioid polar pattern and filtering of GSM radio frequency interference on frequencies from 800MHz to 1200MHz. When fitted into a conference table, the unit provides a very low-profile pickup point; and a touch-sensitive switch with a bi-colored LED halo allows on/off switching when used with a DSP or logic controlled box. The body is finished in nickel and uses an integrated phantom power adapter, allowing the mic to run on 9V to 48V. The CRM 202SRF exhibits a frequency response of 50Hz to 18KHz +/-3dB, and it is supplied with a 6.6ft. two-core + screen cable with open-ended termination.

Dan Dugan Sound Design E-3

Designed by automixing pioneer Dan Dugan, the E-3 automatic mixing controller from Dan Dugan Sound Design puts eight AES/EBU channels and optical connections (ADAT) into a single rack space while featuring both speech and music modes of operation. Up to eight controllers can be linked into one system and each can be controlled on the front panel or from the optional Model CP-2 central control panel, which connects to the rear surface on a 4-pin mini-XLR terminal. Each of the eight channels is equipped with a mute and bypass button on the front surface. Inputs can be partitioned into groups that can span linked units, and multiple devices can be connected on the four network ports.

Earthworks IMB30-B

Less than 1.5in. in diameter and available in black, white, or silver finish, the IMB and IMGL high-definition boundary layer microphones from Earthworks practically disappear into a boardroom table. Featuring an omnidirectional (True Semisphere) pickup pattern, these mics exhibit a frequency response from 200Hz to 30kHz, and they operate on 48V phantom power. The IMBL version also has a dual-color (red/green) LED ring that can function as a touch switch to turn the mic on/off or to operate it in any of its programmable modes. All models have internal shielding against cell phones and other RF sources.

Lectrosonics SPN812

The mixers in the Lectrosonics Aspen line can be stacked or interconnected in any installation, expanding their reach. Specific input/output configurations are made through selection of internal circuit boards, and the SPN812 combines eight inputs and 12 output connectors in a single rack space. All models have a full crosspoint matrix with 48 digital outputs and adaptive gain proportional automatic mixing at the matrix crosspoints. They are controllable through Ethernet, RS-232, USB, and logic I/O ports. In any system using multiple SPN812s, master and slaves are automatically detected and configured. All inputs are line/mic, and the mixing operation can be set for automatic, direct, override, background, or phantom mode.

Mipro has equipped its BC-100 boundary mic to work with a wide selection of ACT wireless microphone system transmitters, and it can operate with either theMM-202 or the MM-202B gooseneck microphones by plugging them into the top for conferences. These can be switched through a back-panel XLR connector into a wired audio system. The built-in hypercardioid electret condenser mic has a frequency response of 50Hz to 20kHz that can transmit through a Mipro bodypack transmitter placed inside the boundary mic case. Aflush-mounted button on the upper surface controls the unit’s transmission and mute.

Peavey S-4

The S-4 4-channel auto mixer from Peavey can be used as a standalone unit, or it can be linked with up to nine others via TRS cables to handle bigger venues. The S-4 offers soft knee compressors on each channel with adjustable thresholds, Mid Morph, and normal high and low EQ, a 12dB per octave low-cut filter, individual channel mutes, insert/direct outs, 48V phantom power, headphone monitor, and an output trim control. There is also metering for PFL signals being monitored on the headphone output, and the insert points can be used for graphic EQ in more demanding acoustic environments.

Rane AM-1

A very useful feature that Rane designed into the AM-1 automixer is the ability to blend a mix of the microphone inputs, which can also be line sources, with the two aux inputs and the USB source. Multiple AM-1’s can be cascaded using Cat-5e/6 cable. An equally handy item is the switchable line/mic output level. The front panel has headphone jacks in 1/4in. and 3.5mm along with a level control and a five-position rotary monitoring source selector. Added features include a USB audio output and a dual recording output. The unit’s RAD port can send digital output on Cat-5 to a Rane HAL system RAD (Remote Audio Device) port or to a Rane Mongoose remote audio router.

RCF AX 8042

Especially suitable for difficult acoustic environments and challenging installations, the AX 8042 DSP matrix-mixer and automixer from RCF has a wide range of adjustable parameters and signal routing configurations. The eight universal mic/line inputs can be fed to six outputs on four lines, and the RJ-45 digital ports on the rear panel allow two of the mixers to be connected. It can be operated though the RCF TS 9918 remote control or through thirdparty devices. There are also 10 programmable logic inputs and six programmable logic outputs.

Revolabs Executive Elite

The InfoComm 2014 award-winning Revolabs Executive Elite wireless microphone system is made for boardroom and conference room applications, and it includes a whole range of hardware items that can be combined in various ways to suit the specific application. The tabletop microphones, with rechargeable batteries, transmit to a remote receiver that connects to the base DSP unit on a Cat-5e or Cat-6 cable, and it supports Power over Ethernet. They are also available in both directional and omnidirectional models, each with a mute button and a light that indicates the microphone’s mute status. The system can also incorporate gooseneck or wearable mics, and a mix of up to eight of any mic types can be placed into the recharging tray.

Samson Technologies CM11B

For maximum pickup area with the minimal microphone presence on the conference table, Samson Technologies has the CM11B omnidirectional fixed charge condenser boundary mic in a low-profile housing that can be mounted on any flat surface using its mounting holes on the bottom surface. Available in black or white, the steel mesh screen cover can blend with the décor, and the low-profile Neoprene rubber pad insulates the case from table thumps and vibration. The microphone body uses a mini XLR connector, and a 30ft. cable is included. The mic operates on 9V to 52V phantom power, and the frequency response is 30Hz to 18kHz.

Sennheiser e 912 S

Versatility is a key for the Sennheiser e 912 S pre-polarized condenser microphone with its programmable membrane switch. Using an internal DIP-switch bank, the mode can be set to push-on/push-off, push-to-talk, push-to-mute, or permanently switched on. A second DIP switch bank controls the frequency response for low-cut, low and high boost, low boost, or linear response. Available in black, white, or Nextel non-reflecting gray, the mic has a rubber damping plate on the base, and its mounting slots allow it to be placed on vertical surfaces as well as tables. Electronics are integrated, and the gold-plated XLR connector resists corrosion.

Shure Microflex

The Microflex wireless microphone system from Shure can be used in a 4-channel or 8-channel configuration that includes bodypack, handheld, gooseneck, and wireless boundary types. With up to 40 compatible channels and adjustable power levels, the components connect via Cat-5e cable, and the systems can connect to corporate networks and third-party control systems using standard networking protocols. The Microflex Wireless Control Software provides remote monitoring and control of all settings and status parameters over the Web, a corporate network, or an AV local area network.

Shure SCM820

Also from Shure, the SCM820 8-channel automatic mixer uses IntelliMix technology and digital feedback reduction, Number of Open Microphones Attenuation (NOMA), and Last Mic Lock-On (LMLO) to ensure the maximum gain before feedback. MaxBus allows only one channel per source and Noise Adaptive Threshold (NAT) automatically adjusts the channel-open threshold. For customized response in a variety of acoustic environments, Intellimix Modes have five different mixing style presets including Classic, Smooth, Extreme, Custom, and manual. Mix A and B outputs offer selectable line/mic levels.


TOA introduced the AM-1 array microphone to detect the direction of the sound source and automatically steer its pickup emphasis toward it. The sound source tracking can be user monitored and manually adjusted through an app on a PC or iPad. Other manually controllable parameters include tracking range, sensitivity, speed, gain compensation, and more. The mic housing connects to a control unit via STP cable. The controller has a Cat-5 terminal for computer connection and an audio output for a mixer channel.

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