Bouncing Off The Walls

Good speech intelligibility during a conference call is rare these days. The reason traces to the fact that most conference room design overlooks one of the most important elements-the room itself and the kind of acoustical environment desired. Solid conference room design must address the need for:

-Good speech intelligibility
-Eliminating reverberant echoes
-Eliminating potential fault areas (HVAC noise, etc.)

Sound waves emanate out from their sources and strike room boundaries in predictable ways. Studies have shown that reflected sound is often inaccurate sound, and controlling that is the key to making a room sound better. With proper acoustical design and treatment, a typical conference room with poor sound quality can be transformed to yield world-class sound.

Hard room surfaces such as concrete walls, glass windows, and tabletop surfaces are responsible for most detrimental reflections. These reflections directly affect speech intelligibility during an audio- or videoconference. The party on the receiving-end of the conference call will hear the direct sound from the person talking, and they will also hear the reverberations from the reflected sound. Often times the reflected sound seems louder than the source sound, and the result is poor speech intelligibility.

Speech intelligibility directly relates to the signal-to-noise ratio in the room. The goal is to have a strong signal coming through on both ends of the call with minimal noise. Noise can originate from the HVAC system, projector fans, or outside traffic. In the case of tele- or videoconferencing rooms, it also comes from reverberation in the room. Reverberation is considered noise in this case because it causes echoes that microphones will pick up. The ideal in maximizing the signal-to-noise ratio is to acoustically minimize everything but the signal or speaker's voice. Today there are excellent ways to eliminate in-room noise sources. These include, if you have the budget, "silent" mechanical systems; noiseless lighting fixture ballasts; remotely located dimmer panel boards; and quieter projectors placed in an acoustically treated, well-ventilated enclosure.

Reflection echoes are controlled by absorption. In part, this can be accomplished through carpeting and acoustical ceiling tile. Some wall treatments are also necessary for audio- and videoconference rooms to maximize the signal-to-noise ratio.

Class A Acoustic Treatment Solutions
In many audio- and videoconference room applications, the design, look, and feel of the room is just as important as the acoustic quality. For such applications, custom fabric-wrapped Class A fire rated (ASTM E84) glass fiber treatments work best. These treatments are available as either a full-wall stretched-fabric system or as a set of strategically mounted fabric-wrapped panels. These panels are specifically designed to absorb sound energy. Fabric-wrapped panels are available in a variety of finishes, styles, and colors that can be arranged in hundreds of combinations.

Noise Reduction Coefficients
The absorptive effectiveness of a sound absorber can be judged by its noise reduction coefficient (NRC). This is a laboratory rating of a material's sound absorption quality. The NRC rating is an average of how absorptive a material is in the four frequency bands considered most important for speech (250, 500, 1,000, and 2,000 Hz): the higher the NRC, the more sound is absorbed in the speech range. There is no absolute number that indicates total absorption, so it is possible to have an absorption device rating well over a NRC 1.00. This indicates a device or material is a very good absorber. For more critical applications, the performance of an absorber in the individual frequency bands should be compared.