Stealth Sound

Sound should be heard and not seen. This is the task of installed sound industry in the archtectural environment. While the modern expectations for sound systems has developed from simple audibility to nothing short of studio monitor quality, there remains an architectural desire to keep the listener from seeing the devices. In applications where a case can be made for the paramount importance of the sound system, there may be greater latitude in exposing this technology to view. However, even in those cases, the loudspeakers are often located in spaces that the structural, lighting and HVAC systems have failed to consume.

The architectural insistence on placing the devices out of the line of view (sometimes from any viewpoint) can often move the loudspeakers away from the appropriate acoustical location. How do you achieve a suitable apparent sound source from loudspeakers that are physically located in the "wrong" location? A classic example of this dilemma is the two loudspeakers on either side of a platform in a church or presentation room. If the architect dismissed a centre cluster in the ceiling, then either side of the talker may be the only option. The loudspeakers may be able to achieve uniform coverage, but the arrival time from each loudspeaker will create large variations in frequency response as you move away from the centre line of the room. In addition, the apparent location of the talker will usually be laterally displaced (any listener not sitting in the centre of the room will hear the amplified voice from only one side of the room). This is a very distracting situation. Attempts to return the apparent source of the talkers voice to the centre of the platform will result in a far more complex loudspeaker system.

A central cluster of loudspeakers can make it through the design process and into the building, but rarely without a struggle. A cluster is difficult to integrate into the design of a room and often takes a prominent visual location. It can be difficult to achieve a good enclosure (acoustically speaking) that entirely suits the "look" of the room while hiding the jumble of loudspeaker hardware. An enclosure may suit the architecture but will the loudspeakers be expected to project through fabric that is almost perpendicular to the device? Even the most acoustically transparent fabric becomes opaque at these angles, and then becomes an unwanted reflector of the sound. A well-designed cluster can perform poorly if it is enclosed by fabric that is too far from being parallel to the front of each loudspeaker.

If we must place the loudspeakers high up in the ceiling, then we must control the directivity, so the sound is focused on the listeners and not to the walls and ceiling. This requires devices large enough to control the wavelengths involved. While many architects imagine loudspeakers to have shrunk in size over the past two decades (to those tiny plastic boxes that come with new computers), if sound quality is an issue then the size of the devices will probably be an issue, too. In sound reinforcement applications, the loudspeaker must do more than just sound good, it must have the directivity control necessary to achieve good gain-before-feedback. Higher up in the ceiling also worsens the vertical offset between talker and apparent source for the listener. We are far less sensitive to a vertical offset than a lateral one (mentioned above) but it is still undesirable.

The sound reinforcement system designer needs loudspeakers that can defy the current physical limitations necessary to achieve bandwidth, directivity control and localization. A thin malleable surface that radiates sound would be very useful. We need a transducer that produces high quality sound but can be manufactured to look like common architectural surfaces, such as wood, gypsum wall board, concrete, stone or glass. The transducer must be capable of directivity while free from problems of interaction between devices. It must produce full-bandwidth sound over the intended coverage area while dramatically reducing the level of sound in all other directions. Finally, the device must produce these characteristics, regardless of the size and shape of the area it can consume. I have seen (and heard) a new technology that might achieve (most of) these important sound reinforcement criteria. However, it still awaits a manufacturer to address a range of issues before a useful product develops from the idea. Stay alert, someday you might hear a loudspeaker even an architect could like.

United Entertainment Media Inc.
460 Park Avenue South, 9th Floor
New York, NY, 10016
Ph. 212-378-0400
FAX 212-378-2160

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