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Everything you need to know about conference room microphones

Michael Garwood 20 September 2017

No pressure, but mics can either make or break your conference room, says technical advisor Justin O’Connor. Here’s a comprehensive guide to choosing what microphone is best for you

Immersive technology is becoming increasingly common. We’ve all seen or used the distinctive head-mounted displays (HMD) used for virtual reality rides or console games, or enjoyed the antics of Pokémon Go hunters seeking augmented reality beasties. But outside of entertainment, where are the strong business cases for AR, VR and mixed reality (where digital and real-world objects coexist)? The answer is in-fact, all around us.

Effective communication can be defined in a number of ways and comprises many elements. In face-to-face discussions, we hear the words and inflections of another person, and we also pick up on other critical input including body language and intentional gestures.

Having a conversation or taking in a presentation is a multisensory experience. Remote meetings employ technology that is intended to provide a multimedia experience that emulates this as closely as possible. Providing video and audio to all participants has become nearly standard for conferencing. While both audio and video content are part of effective remote communication, they are not equal.

If audio becomes unintelligible or is lost, the meeting stops

 Quality audio ‘critical’

Poor video quality or loss of video signal is frustrating and distracting. It can interrupt the flow of communication and collaboration. If the video signal does not return or improve, the meeting can continue without video and documents can be shared by email if necessary. If audio becomes unintelligible or is lost, the meeting stops. Even if video remains, without audio the meeting will stop until the problem is rectified. If it is not, the meeting will most undoubtedly be rescheduled. Video is important to communication, but audio is absolutely critical.

The distraction can range from annoying to detrimental. Even having to strain to understand the far end of a call can limit the creative and analytical thinking that makes collaboration efficient and more productive.

There are many factors that influence good audio quality. First and foremost is the capture of the spoken word. Good capture relies on good microphones, the right type of microphones, and attention to room acoustics. Getting the microphones right can go a long way to overcoming other potential detractions in the audio path. Getting the microphones wrong will absolutely cause problems that cannot be mitigated later in the signal path. Microphones will make or break the effective audio communication from your conference room.

But before looking into microphones, there must be some consideration for acoustics

Acoustics

But before looking into microphones, there must be some consideration for acoustics. It isn’t always feasible architecturally, aesthetically, functionally, and financially to deploy acoustic treatments in a conference room. Anything that can be done to address acoustic matters is helpful. In most conference rooms, the typical acoustic problem is reflective surfaces. Construction and furniture materials that are hard or glossy tend to reflect sound frequencies that are critical to the intelligibility of spoken words.

In a room that can accommodate 12 to 15 people or fewer, these reflections are unlikely to impact intelligibility for the people in the room when listening to a person speaking. In the case of microphone capture, these reflections can impact the intelligibility on the far side. These reflections arrive at the microphones later than the original sounds. If they are nearly as loud as the original signal when they arrive at the microphones, they will obscure parts of the words being spoken.

In a highly reverberant room, there will be many late arriving reflections and they will retain enough of their original sound pressure level as to be audible and mask the words of the person speaking.

Tackling reverberation is best done by adding as many soft, and therefore sound absorbing, materials to the room as is possible

Tackling reverberation is best done by adding as many soft, and therefore sound absorbing, materials to the room as is possible. Drapes, and carpet are excellent choices as is the hanging of art that is on large canvases, rather than prints or photographs covered by glass. Any step that can be taken to mitigate reflections will improve the intelligibility at the far end.

Microphones – the technical bit

Microphones capture acoustic energy and convert it into electrical signals. Most typical microphones have a diaphragm that physically responds to the air pressure oscillations of sound. The diaphragm, attached to a coil of wire, moves sympathetically and the coil passes through a magnetic field generating an electrical signal that is representative of the acoustic energy.

Microphones have a variety of pickup patterns, which determine where the efficiency of the microphone is greatest. Three common patterns are: omni-directional, which has an equal pickup in all directions; cardioid, which has a null point at the back of the capsule; and super cardioid and hyper cardioid, which while having a small lobe at the rear, have greater directionality of the primary pickup lobe. These patterns are represented by polar plots, as shown on the image to the left.

The best microphone placement and type would be a directional microphone for each individual, within a few inches of their mouths

Good capture quality from a microphone is about ratios. Since the capsule, even in a directional microphone, will pick up sound energy from more than one direction, the reflections of sound throughout the room will be picked up. If the relative energy difference between the original spoken words and the reflections is low, the sound quality will not be as good. If the ratio between the original speech and the reflection is large, the intelligibility and quality of what is captured will be much better. In the case where the energy of the reflected sound is closer to the original, the listeners at the far end will perceive the room to be large, “cavernous”, and “echoey”, and the perception is that the people talking are far away from the microphones. (In some cases this is indeed because the people speaking are too far from the microphone)

The best microphone placement and type would be a directional microphone for each individual, within a few inches of their mouths. This reduces the impact of the acoustics of the room as the comparative level of their spoken words to that of the late reflections will be much higher. All sound energy dissipates as it travels through air. If the original spoken words only pass through a few inches of air space, and the reflections travel all the way to a wall and back, for example, the energy will have dissipated, even in a highly reflective room. There are many factors that influence whether this type of microphone approach is feasible in a conference room, including budget, furniture, aesthetics, and room functionality. The closer the solution is to a single microphone element in close proximity to each person in the room, the better.

Tabletop microphones

Tabletop microphones can take on various forms. Gooseneck microphones with a base on the table and a neck extending the microphone up to the person speaking are arguably the best acoustic approach. They are, however, often considered visually unappealing and some people experience discomfort with a microphone in front of their face and speak more softly. Also, depending on the pickup pattern and how animated the person speaking is, they may move out of the pickup pattern while speaking. Other table top microphones are low profile boundary mics that sit very close to the surface of the table and even use that boundary surface to increase their efficiency. These help with the worry about people moving out of the pickup pattern, but it also means the microphone element is further from the person speaking. An additional concern is that the microphones can be blocked by laptops, covered up by papers, and tend to pick up noises at the table.

Ceiling microphones

Ceiling microphones hang from the ceiling and capture the sound of speech from above. This solves some of the disadvantages of tabletop microphones by getting the microphones off of the table. They can’t be covered by papers or blocked by laptops, and they are less likely to pick up table noises.

Ceiling mics are also generally less noticeable as they are above the sight line. If enough ceiling microphones are installed and placed properly, they can account for people getting up from the table while speaking and they are also an effective for avoiding issues such as running cable on top of or through tables, and aesthetics.

Ceiling mics are also generally less noticeable as they are above the sight line

They are, however, further away from the people speaking. While most ceiling mics allow for variable installation heights to accommodate different ceiling types, they will essentially always be further away from the people speaking than a table microphone. Ceiling mics may be less likely to pick up table noise, but they end up in close proximity to other noises such as the fans of projectors.

Beamforming microphones

Beamforming microphones have been increasing in popularity and in the number of options available. Most are available in either ceiling mount or tabletop versions, but they differ from single element, traditional microphones due to the array of acoustic capsules they feature. A beamforming microphone array uses multiple elements that are forming a large pickup pattern.

When a person is speaking, the signal strength of that speech at all or some of the elements is compared by processing algorithms to determine where the person speaking is located with relation to the array. The processing can then focus the pickup of the person speaking by adjusting individual capsule levels to increase pickup of the person speaking and increase rejection at other parts of the array. Advanced approaches to this processing allow the beamforming array to track the person speaking if they are moving, and in some cases will support multiple simultaneous beams.

There is no one size fits all answer to microphones

Final thoughts…

There is no one size fits all answer to microphones. Even rooms that have the same size table and the same number of chairs may well need different microphone approaches based on acoustics, aesthetics, or room functionality. While it is advisable to have standardisation in conference rooms within an enterprise, this standardisation should be reserved to user experience and control, and to infrastructural technology.

Microphone selection requires intentional decision making based on the various influences. The result may be that many rooms share the same approach, but if this arrives from careful consideration of the challenges, needs and the input of a knowledgeable professional, the results will be far more effective and of much higher quality than attempting a single answer to all rooms.

 

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