Boardroom audio
May 1, 2000 12:00 PM, Dale Florence
Although new video technology is often specified by the client for the modern conference room, achieving good speech intelligibility remains critical to an installation's overall success.
Today, customer expectations are high. Television and movies have set standards of elaborate boardrooms and control centers where anyone inthe world can be seen, heard and communicated with by the press of a button or by a spoken command. Despite the fact that these types of representations involve fantasy - perhaps including violations of the laws of physics but especially regarding the budget for the room - business people have come to expect this level of hands-free communication and ease of use in their own office spaces, and they want you to design it.
Although technology is coming closer to meeting this promise, budget restrictions will continue to restrain full implementation of the newest technologies by all but the largest of corporations. Still, many boardrooms have complex, integrated systems consisting of multiple products, including remote control, audio, video and data-sharing components. Boardrooms, however, are for communications, and at the heart of every communications application is the audio system. Even the most simple boardroom design will have some type of audio requirement. With this in mind, we will focus on the basic elements of a boardroom sound system and how best to meet the customer's needs.
The first step in meeting the needs of a customer is to find out how he is going to use the system and what performance level is expected. If an architect or acoustical consultant is designing and specifying the system, most of this work will be done before the contractor becomes involved, but we will assume that you get a call from a small- to medium-sized business that wants to build a boardroom or add audio to an existing meeting room without going to an architect or consultant. This is the time to help your customer define the scope of the project.
Next, identify the customer and his expectations. Set up a meeting with the customer to discuss the project. Talk to the individuals who will use the room as well as the technical staff that will be involved with the day-to-day use and operation of the system. Each will have a different idea of what is wanted from the system. Resolve any unrealistic expectations and help the customers determine what they actually need. Ask a lot of questions up front.
Additionally, knowing how the room will be used is absolutely necessary in order to design and install a system that will meet the customer's needs. How big will it be? How will it be built? What are the walls, floors and ceilings made from? Is it a multi-purpose room? Can the room be divided with multiple meetings taking place simultaneously? What kinds of presentation media will be used? Will they be using remote conferencing? What about video? Common uses include playback of prerecorded A-V sources, viewing satellite or TV programs, speech reinforcement within the room, and teleconference or videoconference sessions. Suggest uses from your experience to make sure the customer is not forgetting important applications.
If you are installing in an existing room, be sure to check it out completely. If the room exists on the drawing board, talk to the architect and designers. One of the first principals of working with sound is knowing the distance that it has to travel. Is sound reinforcement necessary? Remember basic principals; for example, how many loudspeakers will be needed and what their best placement should be. A room with a low ceiling will usually require more loudspeakers than a room with a higher ceiling to ensure sufficient coverage. Surprisingly, medium-sized boardrooms often have better acoustical properties than smaller or larger rooms.
Existing boardrooms or offices to be converted for boardroom use will likely have wall surfaces made of plaster, gypsum board or paneling with carpeted floors and acoustical ceiling tile. Newer boardrooms will incorporate modern designs featuring glass walls, marble floors, high ceilings and large, hard-surfaced tables. Each of these surfaces absorbs or reflects sound waves in different ways.
The absorption characteristics vary in relation to the wavelength of the sounds in the room. Reflections can cause sound waves to combine slightly out of phase and cancel each other out, causing dropouts or dead spots in the room. Sound waves can also combine in phase and cause the system to become unstable, which leads to feedback or hot spots where the sound is more concentrated. In addition, sound waves can bounce back and forth between flat, parallel wall surfaces and create standing waves at the resonant frequency of the room, which produces unwanted acoustic energy.
Eventually, all the reflections in the room will become incoherent and out of phase. Reflections and standing waves combine to form acoustic energy called reverberation. As reverberation increases, intelligibility diminishes, and people in the room will be able to hear but not understand what is being said. When a person cannot understand speech, his or her first impulse is to turn up the volume, which only adds to the reverberation problem. In this case, turning the volume down a little may be all that is necessary to bring back intelligibility.
Aesthetics vs. acoustics
Architects and interior designers strive to satisfy their customers by creating rooms with high-gloss aesthetics and stunning visual effects. These rooms may look great, but hard surfaces inherently have poor acoustics. Curved walls and domed ceilings cause the biggest problems of all. Curved surfaces tend to focus sounds to particular places in the room. If the focal point occurs at a mic, feedback will be an inevitable reality.
Acoustical treatment may be necessary if echoes, reflections or reverberations render the sound system ineffective or counterproductive. Absorption panels can be added to walls to reduce reflections and reverberation. Draperies can be placed in front of windows and glass walls, which can normally be left open but must be pulled closed during meetings to provide a more cooperative acoustical environment.
A dollar spent improving room acoustics may save many times the amount required to overcome poor audio quality electronically. Plan in advance to overcome poor room acoustics. Explain both the problems and the possible solutions to the customer. Whether the boardroom is being newly constructed or remodeled, addressing acoustical concerns before work begins can prevent a lot of unnecessary frustration and expense for customers and contractors down the road. Compromised acoustics require an optimized audio system that will be more complex and expensive. If the customer cannot afford the system, the sale will be lost.
Consider the room layout. How flexible is the room? Can it be sub-divided for simultaneous meetings? Ask about furniture arrangement in relation to how the room will be used. Make sure to note the location of tables and chairs, and be prepared to make suggestions. Be sure to take multiple-use layouts that might preclude having tables in fixed locations into account.
Next comes local speech reinforcement. Amplification of speech that originates within the same room is considered local speech reinforcement. The goal is not to make speech louder but to extend the speaker's voice to every participant in the room. Someone who is seated on the last row of a meeting room should be able to hear the person speaking just as easily as someone seated on the front row.
Most small boardrooms do not need local speech reinforcement simply because meeting participants are seated relatively close to each other. Some boardrooms, however, may require amplification because of their size or the acoustics of the room. In addition, speech reinforcement might still be required for meetings that include people at distant sites or to reach people seated in another room set up to accommodate overflow attendance. Again, we are talking about extending the audio rather than making it louder.
Mics in the boardroom
Simply stated, mics should be placed close to the person talking. Although this statement may seem obvious, it is one of the most significant factors in determining the performance of the audio system and one of the biggest challenges for sound contractors. We have not yet found a mic on the market that can discriminate between sound from the person speaking and other noise in the room. As a mic is moved farther away from the person speaking, the loudness of the speech reaching the mic is decreased. To compensate for the loss in volume, mic gain must be increased, which leads to a greater possibility of feedback and will amplify background noise as well. Finally, the farther away the mic is from the person talking, the more hollow and distant the audio will sound.
Because they can be closer to the person speaking, tabletop mics will generally do the job better than ceiling mics. The biggest problem with tabletop mics is that they are in the way. Place tabletop mics so that papers and charts will not interfere with the path of sound between the mic and the person speaking. There are some imaginative table designs that accommodate mics as well as a variety of other must-have electronics, such as network access for laptops.
Customers often demand ceiling mics. Make them aware of the issues. In addition to problems created due to the distance from the person speaking, mics that are mounted directly to the ceiling can pick up rumbling sounds from vents and air-handling equipment. Although ceiling mics can work, the acoustical treatment required may not be worth the tradeoff. Hanging mics can work in rooms where furnishings need to be moved around for different types of meetings. Be sure that hanging mics are not in the direct path of sound from nearby ceiling-mounted speakers.
Critical distance must also be considered when locating mics. Critical distance is the point where the loudness of a person's voice is equal to the loudness of reverberant sound in the room. The critical distance of a room is unique to the room and its acoustics. Measuring reverberation and calculating critical distance requires special test equipment. Although space does not permit a complete discussion of critical distance here, a general rule is to provide a good acoustical environment with mics located as close as practical to the person speaking.
More mic tricks
An automatic mixer should be used to turn mic inputs off and on as needed. An automatic mixer's gate inputs open when the incoming signal reaches a fixed or predetermined threshold. In practical terminology, this means that they turn the mic on when someone is speaking then turn it off when they are quiet. This minimizes mics' picking up HVAC or other constant background noise. The best automatic mixers also compare all of the mic inputs in relation to each other and in relation to noise in the room. If the signals picked up by all of the mics connected to the mixer (such as background noise) are equal, then the mixer will keep the inputs gated off.
Turning on additional mics will increase the potential for feedback. Automatic mixers can use the number of open mics as a reference to compensate for feedback considerations. As the number of open mics increases, the output level of the mixer is turned down. Doubling the number of open mics requires an overall reduction of 3 dB at the mixer's output.
Electronic feedback eliminators, EQs or other types of signal processors can be used to achieve maximum gain before feedback in the audio system. Be careful to avoid over-equalization. Too much tweaking can result in unnatural sound and listening fatigue for the occupants of the room.
Other issues
Use data sheets, manuals and tech notes from loudspeaker manufacturers to determine loudspeaker placement in the room. This will ensure adequate coverage of all seating areas. Choose power amps to match loudspeaker load requirements. Overrate the amp power 20% to 30% to provide headroom for peaks in audio level. This will prevent overdriving and clipping of the amp's output signal and allow for better dynamic range.
As we extend the audio to all of the participants, do not forget the hearing-impaired. Assistive listening systems (ALS) should be included under the guidelines of the Americans with Disabilities Act. Generally, this requires assistive listening for 4% of the total seating capacity in relation to the maximum seating for any use of the room. For rooms seating less than 50 individuals, no less than two ALS-equipped seats are required. Assistive listening is usually accomplished with a wireless mic or transmitter and a personal receiver for hearing-impaired individuals. Remember that radio transmitters and wireless mics can transmit signals beyond the confines of the boardroom.
Program audio
Audio from sources other than speech reinforcement, teleconferencing or videoconferencing is often referred to as program audio. A program audio system is usually the easiest to design and install in a boardroom. Audio tape, CD, VCR, DVD and telephone, television or satellite audio needs to be heard by everyone in the room. This may require a high-end reproduction system, perhaps even surround sound.
If possible, design a program audio system that can be used independent of speech reinforcement and teleconferencing systems. Separate systems can simplify control and provide a better S/N ratio and an increased frequency response.
Choose professional-grade playback devices, rather than consumer-grade types, for best audio quality. The higher output levels from pro-audio devices will allow inputs of mixers or switchers to be used at unity gain. Adding gain at input stages not only increases the program audio level, but it also amplifies any noise or distortion. Try to keep levels throughout the system at unity gain until the final power amp.
Use loudspeakers of good quality, matching the power amp to the loudspeaker's power handling characteristics. For surround sound, consider using a matched system of amps and loudspeakers supplied by one manufacturer. For best results, follow the manufacturer recommendations regarding loudspeaker placement and system connections.
Teleconferencing
Teleconferencing requires two-way communication. The local audio needs to be extended to a far site, but the far end audio needs to reach the local site as well. A telephone line can connect the sites, but the send and receive audio exist on the same pair of wires. Routing a portion of the transmit signal back on the receive path is called side tone or line echo, and on a regular telephone handset, it is desirable. Hearing yourself on the earpiece helps determine how loud you should speak.
Now, connect the same phone line to the input and output of a sound system. What happens? The local audio is applied to the phone line; far end and local audio is brought into the system. The result is instant echo - if not severe feedback. A telephone interface device called a digital hybrid is required to remove echo of this type. The digital hybrid samples the local audio before it gets to the phone line. The sampled audio is then inverted 180 degrees and combined with the audio from the phone line before being sent to the amp and loudspeakers in the local room. Because the sampled local audio is 180 degrees out of phase from the original local audio, the two signals cancel each other out.
Digital hybrid telephone interfaces can be purchased separately and integrated into the system in order to teleconference with more than one distant site at a time. Some echo cancellers have the digital hybrid built in, eliminating the need to purchase a separate component.
We have fixed the phone line issues, but we now have audio from the far end passing through the amp to be heard from the loudspeakers in the local room. Everything is great, right? Wrong. The audio from the loudspeakers will be picked up by mics in the local room and sent back to the far end. The far end will hear an acoustical echo that is generated in the local room.
Acoustic echo cancellers are used to sample the audio from the far end before it gets to the local amp and loudspeakers. Local audio, picked up by mics in the room, contains audio from the person speaking in the room as well as far-end audio emanating from the loudspeakers in the local room. The sampled far end audio is applied, 180 degrees out of phase, to the audio picked up by the mics. This cancels out the far end audio before the signal is sent back to the far end.
The digital signal processors that exist in the echo canceller allow for simultaneous local speech reinforcement and teleconferencing. Because the far-end audio has been sampled and removed from the mic audio, the portion of mic audio containing only local talkers can be sent to the amp and loudspeakers in the local room.
A successful conference requires clear audio. What if you are working with a spectacular boardroom - that is, one with glass walls, marble floors and a hard table? You need conferencing equipment that optimizes audio performance to deal specifically with these acoustical challenges.
Distributed echo cancellers have a separate echo canceller on each individual mic input, which enables each echo canceller to converge at a faster rate to quickly eliminate the echo. Changes in audio levels, mic placement and room acoustics are instantly accommodated. Some echo cancellers have an automatic mixer built into them. All audio signals are converted to digital information before any sampling, echo cancellation or mixing takes place. Because the mixer is an integral part of the echo canceller, the mixer's inputs can be set to respond only to a voice in the room. The automatic mixer can then ignore any and all audio from the loudspeakers. In addition to providing hands-free teleconferencing, this feature greatly enhances local speech reinforcement. Saving the expense of a separate automatic mixer is another benefit of using combination echo canceller or auto mixer devices.
Two separate rooms require two separate acoustical echo canceling products. The reference for each echo canceller is based on its own room. In instances where moveable walls or partitions installed between two rooms are opened to create one large room, that room will require only a single echo canceller. Rather than installing two separate distributed echo-canceller products, choose one that has two references. For combined use, route all of the mic inputs to use one reference. For two-room use, route half of the mic inputs to use one reference and half to use the second reference.
Clearly, audio is only one part of designing a great boardroom. When you think about why people meet, however, it is obvious that it is the most important. If the projector fails, you can always describe the chart. If the video blinks out, you can cope. Without audio, communication breaks down, and you no longer have a meeting.
No one needs to feel intimidated by the prospect of providing excellent boardroom audio systems. The variety of available equipment offers solutions to a variety of challenges; knowing what to plan for is the biggest hurdle. In many ways, great boardroom audio has never been easier.
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