Technology Showcase: Boardroom Microphones

One of the easiest misconceptions is to run with a one-size-fits-all mentality. Many mics, speakers, and electronic modules work excellently on the presentation
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Technology Showcase: Boardroom Microphones

Feb 1, 2004 12:00 PM, By Allan Soifer

One of the easiest misconceptions is to run with a one-size-fits-all mentality. Many mics, speakers, and electronic modules work excellently on the presentation stage or in an institutional setting but are less than perfect in the corporate boardroom environment. Here not only is high-quality audio a must-have but the installation must be configured for minimal intervention by technical personnel and be aesthetically pleasing to the client, as well. This article will touch on some of the key points of using mics in the corporate boardroom environment and will offer a listing of the major manufacturers of mics applicable for boardroom use. Products featured in this article are standalone microphones or packages. Conferencing systems are not included in this overview.

Most of the difficulties that integrators experience in the corporate setting stem from microphone use and placement. The corporate types who often participate in meetings seem to exhibit a lack of concern for speaking close enough to a mic to be heard clearly over acoustic ambience or switching their mics on and off. That is an annoyance and aggravation for the technical producers of a boardroom event (especially if remote conferencing is involved) and any interpreters or translators who might be struggling to provide top-level interactive service with less-than-ideal listening restrictions. Truth be told, those corporate types are footing the bill, and thus they are entitled to expect the behind-the-scenes personnel to do the tech work on their behalf. So setting up a bunch of cardioid mics on table stands and running the cable snake to a nearby closeted mixing system will just not do.

So big deal you say; a mic is a mic is a mic, right? Not true. Some real physics are present, which conspire against straight, clean, and simple. Let's begin this showcase with one of the more unusual yet useful devices, the boundary mic.


For basic recording and one-way transmission of audio, an elegant and simple solution to the electronic and aesthetics problems may be the boundary mic, with several of them laid out on the boardroom table. The very nature of the boundary mic beast is near-perfect hemispherical pickup. (Incidentally, the term pressure zone mic, or PZM, is often used in place of boundary microphones. However, PZM is a trademark of Crown Audio. See the sidebar “Pressure Zone Mics” for more information.) Boundary mics are low profile, unobtrusive, and ideal for use on flat surfaces. Studios and live recordists have been using them in stereo pairs for many years as an alternative to multimic technique. However, if simultaneous interpretation or translation/closed-captioning transcription will be a factor, then the omnidirectional attributes of typical boundary mics may become a liability rather than an asset. Several sources offer omnidirectional and directional boundary mics.


Directional mics seem to constitute most of the installed or leased equipment for boardrooms around the world. They are coupled with special shockmounts for table-thump noise reduction and individual electronic packages for mic control, interpretation interaction, and even voting tabulation. Directionals and hypercardioids are the most often found types among corporate audio installations. The design factors inherent in creating a directional microphone allow the instrument to reject much of the sound pickup from the sides and rear. Placing a unidirectional mic reasonably near to (less than 24 inches) and on axis with a speaker's lips will give optimum results.

To expand just a bit on the boundary mic idea, there are directional boundary mics, as well, which deserve consideration for boardroom use. An integrator can really prove his or her worth to the client through careful discussions about the intended use of the boardroom environment. Meetings that regularly require interpretation, live translators, or video support for conferencing or press involvement mandate directional microphony — different from those events that simply need recording for corporate minute taking and archival purposes. Industry standards and practices often require that a live mic have a red indicator LED to alert the participant and ancillary personnel to the mic's active condition.


One of the largest mic makers anywhere is Shure. For boardroom and corporate applications, a number of models are offered. The MX400 series — the MX412 and MX418 are representative — can be had in different gooseneck lengths and configurations and with or without bases, silent muting, LED indicators, and other options. Microflex is Shure's product line name for boundary microphones, and all Microflex models feature an interchangeable condenser cartridge. They are available in cardioid, supercardioid, and omnidirectional polar patterns, with features like programmable silent membrane switches, logic inputs and outputs, and LED indicators. Shure supplies these low-profile mics with an easy-to-use paint mask for custom color installations. The wireless Microflex MX692/C boundary microphone features more than 100 selectable channels through its integrated wireless transmitter.

Crown Audio is a major supplier and manufacturer of PZMs and conventional mics, as well. Having been the first to pick up boundary technology, Crown offers a variety of various omni- and unidirectional instruments to suit almost any contracting need. The PZM 20R is designed for flushmounting in a conference table, and the PZM 6D and 30D are engineered for dual response curves — flat and rising to enhance speech pickup. Crown also makes some nifty miniature boundary mics. These are interesting for concealment in the boardroom and surveillance and security use. From the conventional side of the coin, Crown's CM30 hanging condenser cardioid is good for recording, thus making it ideal for good speech pickup.

Astatic is a firm founded by two ham radio operators who wanted better mics for their rigs. The company is notable for manufacturing almost all of its assembly components in house, including its famous shockmounts, which have vastly improved table and podium mic installations. Astatic offers three boundary mics. The Astatic 201 and 202 microphones are miniature, high-performance electret condenser microphones designed for low-profile mounting in panels, tables, or ceilings. Both are 1.1 inches in diameter at the largest point and mount in a 13/16-inch opening in panels up to 2 inches thick. Each mic has a built-in, switchable highpass filter and color-matched shockmount isolators. The cardioid (half cardioid above mounting surface) pickup of the 201 pattern may minimize annoying feedback when used close to sound-reinforcement speakers and monitors while reducing the pickup of unwanted off-axis sounds. Astatic's model 901 is a more conventional boundary mic for tabletop use.

Sound Control Technologies offers various mics and electronics for audio and videoconferencing and distance-learning installs. It provides a different slant on boardroom mics. The SCM-4 features the use of slender, wand-mounted elements suspended from the ceiling. These microphones are available in custom lengths starting at six inches. The basic premise of these mics is to bring the working element down from high ceilings to a comfortable height in order to reduce room reverberation and ambient effects often picked up by ceiling mics. The SCM-4 uses a cardioid microphone element to achieve some rear cancellation of noise and reverberation while maintaining an effective omnidirectional coverage pattern in the working space of the conference environment. The SCM-2, a standard flushmount mic for ceilings or tabletops, is also available.

Electro-Voice is still a major player in broadcast and recording mics. It offers a hanging mic, the RE90H, and a boundary mic, the RE90B. A distinctly different mic is the PolarChoice, a conference table mic with selectable polar patterns (omni, cardioid, supercardioid, and hypercardioid) and permanent or portable mounting. The PolarChoice Satellite adds wireless flexibility to the mix. The base in the Satellite provides housing for an Electro-Voice or Telex body-pack transmitter, including the Safe-1000 encrypted secure wireless system.

Audix offers several alternatives, including a boundary mic (the ADX60) and some hanging and gooseneck mics, such as the ADX 112 and 118. The company also offers an accessory base, the ATS10, that has an off/on switch and input and output XLR connectors so that a variety of gooseneck and mic options can be employed.


Neumann is the studio mic giant. Though the company doesn't offer anything specific to boardrooms, many of its products are certainly of use in high-quality sound recording and transmission events. The Neumann KM100 is a podium or tablemount microphone of the wand type.

Sennheiser is a well-known name among recordists, audiophiles, and professional users. The Contractor Mic Kit (reviewed in the December 2003 issue of Sound & Video Contractor) features a selection of gooseneck and mic element options, including cardioid, supercardioid, and supercardioid/lobar polar patterns. The classic MD-421 and 425 series are not tiny and require desk stands of various types, but they are among the best in class for broadcast and studio-quality voice pickup. That can be an important factor if your boardroom inhabitants intend to hold regular press conferences or do any online distance conferencing.

Beyerdynamic is also a major contender in the mic field. The company has been in the professional audio business since 1924, when it was founded to design and manufacture loudspeakers for the German cinema industry. Beyerdynamic lays claim to presenting the first true dynamic headset, the model DT-48, which is still in production today and is a standard headset for live motion-picture recording techs. The boardroom offerings are boundary-style mics, with the newest being the MPC 67 RC. This mic is available with a remote control; the microphone can be activated by an external switch, and an external device (such as a video camera) can be triggered by its MOSFET output, which makes it applicable to semiautomated videoconferencing as well as video logging of meetings. The MPC 67 is offered with linear (flat) response and can be switched to 80 Hz or 180 Hz bass rolloff.

AKG is another major European audio manufacturer that grew from small beginnings to become a world supplier of professional mic technology. Like beyerdynamic, AKG began as an engineering effort to improve the audio quality of motion pictures in their infancy. The company's choice offering for boardroom installs is a hypercardioid boundary mic, the C400BL. The C562CM boundary microphone is designed for permanent, invisible mounting in ceilings, walls, tables, stage props, and so on. Owing to its high sensitivity, the C 562 CM is a perfect tool for surveillance or live recording because a single microphone can cover an entire room. Such coverage essentially trades off directionality, but it is useful if simple audio pickup is mandated and there's no need to visually identify the speaker (as in conferencing or interpretation events).

Schoeps is a German mic maker that holds the distinction of being the favorite and mandated standard of Hollywood motion-picture sound recordists for many years. The company offers several boundary mic models, but they are not geared or exceptionally open to the A/V market and are priced astronomically high. Still, if you have a client who wants the most expensive stuff to boast about, this company would be one to investigate. These mics must be obtained from Schoeps-selected U.S. reps. Address serious inquiries to the parent company in Germany (through its Web site) to determine the status of any American dealer.

DPA manufactures a variety of microphones and is probably best known for producing measurement mics and miniature mics for use in theatrical sound reinforcement. DPA offers a selection of compact mic capsules as well as a number of elegant mounting solutions that would apply in conferencing solutions.


Audio-Technica is a popular manufacturer of professional microphones and related technologies. For boardroom installs, it has ceiling-hung mics and boundary models. The Pro-45 is a top-end hanging mic with self-contained electronics to eliminate the need for an outboard power module (phantom power is required). This high-end mic is touted for recording and broadcast of choirs and orchestras, so it will offer excellent voice pickup. The mic is furnished with a windscreen and a proprietary steel hanger. The Pro-44 is representative of the line of tabletop boundary microphones. Like its hanging cousin, the Pro-44 has a self-contained electronics package, allowing it to plug and play directly in to any console or mixer that is equipped to provide phantom power.

Canadian company Clockaudio offers boundary layer mics such as the Stingray C008E, its top-of-the-line cardioid; and omni models, low profile (the C004E), and ceilingmount mics.

Some of the mic makers also produce and market related components such as automatic mixing systems, interpretation interfacing, conferencing, and voting equipment, all of which have direct boardroom applications. These other boxes and toys are not within the purview of this article, but a look at the companies' Web sites will prove interesting and informative. Now all you need is a deluxe coffeemaker, and you're set to provide quality boardroom audio service.


The PZM is a distinct contribution to microphone technology. It is a drastically different acoustical pickup characteristic as compared with other conventional mics. The history of the PZM is inexorably intertwined with Don Davis, the originator of the Syn-Aud-Con seminars, and it is one of Davis's early graduates of those landmark trainings. The story of this mic's inception can be read on Crown Audio's Web site ( and by clicking on the archives of Crown's Mic Memo newsletter. The late Ken Wahrenbrock, the PZM's developer, wrote and compiled these memo/newsletters.

Consider that since Alexander Graham Bell devised his telephone, not much had occurred in the basic development of mics. Regardless of improved materials and electronics, a microphone still had to have its diaphragm placed near enough to the sound source to be of any use. Directional mics tend to suffer from certain anomalies based on time and frequency shifts that produce audible artifacts and alterations in the acoustic waves that they intercept and convert to electrical energy. The PZM was a developed strategy, based on careful investigation and research, to minimize and even to negate the effects of acoustic wave interference in microphone use and placement. For purists the correct terminology is the boundary microphone, with PZM being Crown Audio's trademarked name. The concept is rather basic in its physics: a pressure-calibrated condenser mic capsule is mounted in certain ways within a sound field.

Such a mic element — when flushmounted in a large, smooth area within the general region of acoustic (sound) waves — has its on-axis response essentially in a free field. Sound is understood to be in a free field if it is a uniform wave, has no boundaries causing reflections, and no other sound waves nearby cause a disturbance. When placed within a cavity (a pressure sound field), this mic will have a response that is uniform with frequency. In the PZM system, no signal can ever arrive directly on-axis — sound can enter only at the sides of the opening, between the mic's diaphragm and the boundary plate. That means the PZM not only has a flat response but exhibits this characteristic for all angles of incidence. In real-world audio, that means no more comb filtering or hollow sounds when someone talks or sings somewhere near the mic but not directly in front of it. That is what sets boundary mics apart.

Other mics, no matter how well designed or expertly built, receive a mixture of direct and reflected sounds at different times upon their diaphragms. That creates frequency spikes and acoustic anomalies. Indeed, the very difference in time/energy/frequency is what creates the cardioid patterns that identify some mics as being directional. Directionality is often a needed quality, but it is derived at the cost of acoustic perfection. A boundary mic always sees the pressure field at the surface of its boundary, and that field is completely free of the glitches caused by interaction of direct and reflected sound waves.

The construction of a boundary principle microphone is inexpensive in relation to making other mics. It is essentially a plate of metal with a mounting arm holding the pressure-calibrated electret mic capsule fixed in position just slightly above the plate. Aside from the mechanics of the mounting and connector, nothing else is needed. In fact, Radio Shack licensed the idea for a number of years and marketed a PZM for about $50, and that particular model had almost identical response to the much costlier professional models offered by Crown.

Boundary mics have fewer restrictions in terms of placement and mounting. Anything is good, so long as one does not mess up the smooth boundary plate that creates the field.

For More Information

AKG Acoustics






Crown Audio

Crown Audio

DPA Microphones





Sound Control Technologies

Allan Soiferis a recordist, a broadcast consultant, and a regular adviser to several Canadian governmental groups in the areas of audio, video, and interpretation/conferencing support. He can be reached




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