By Richard Schrag
Recent news articles1 indicate a trend in classrooms that many acousticians find disturbing: Elementary school teachers are being given sound reinforcement systems. On the surface this may seem like a worthy idea, and studies do show that students learn better when they hear better. However, in a well-designed small mainstream classroom, voice amplification should not be required in the first place. Amplification systems are often a way of "fixing" classrooms that are too noisy and too reverberant to begin with. The better solution is to address the problem at its source—making HVAC systems quieter and providing surface treatments that enhance intelligibility.
If a space's basic acoustical needs—adequate sound isolation, noise and vibration control, and appropriate room acoustics—are not met, other technological means of overcoming problems may only exacerbate them. In most types of acoustical environments, the goal should be to address the "natural" acoustical background before applying technology fixes.
For classrooms, voice amplification is usually not the best solution. Despite the brain's remarkable ability to distinguish speech from noise, in noisy environments it must work much harder to understand the spoken word, ultimately detracting from its ability to process the content. Raising the talker's sound level can improve the signal-to-noise ratio but only by making everything louder, which may be just as fatiguing for the listener. Also, amplifying the teacher's voice addresses only the problem of teacher-to-student intelligibility; it does not improve student-to-teacher or student-to-student communication. This is a case where technology is a work-around for a problem that can be better solved with good acoustical design.
Other building types provide similar examples. To ensure that the spoken word can be understood over air-conditioning, houses of worship often just make the sound reinforcement louder. An extra 3 dB of background noise can dramatically increase the complexity and cost of the sound system. Moreover, an electronic system generally cannot overcome poor natural acoustics. If the sound is "muddy" because the venue is inherently too reverberant, you can't expect that more sound amplification will fix it.
Open office environments are susceptible to the "cocktail party effect," in which the ambient sound level in a space rises disproportionately from competition among multiple conversations. If sound is allowed to bounce around surfaces with inadequate absorption properties, the guy with the booming phone voice (even though he's four cubicles away) makes everyone else talk louder. If a sound masking system is put forth as the solution to this problem without the accompanying fixes to the "passive" acoustics, it will need to be set at a higher-than-desirable level to overcome the general cacophony. The workers won't be disturbed by "loud guy" but now their open office will sound like a freeway even when he isn't on the phone.
A related phenomenon can be experienced in hotel meeting rooms with operable walls. If the partition is not providing adequate sound isolation, sound that comes from the meeting next door may be audible. The typical (technological) response is to raise the level of the AV system, increasing the amount of noise that leaks through to the other space. This prompts the group in the adjacent space to raise its level, escalating into a situation where the reinforced sound in both rooms is much louder than needed but is still not intelligible.
Technology solutions can be a necessary and useful extension of a room's acoustics. Sound reinforcement systems are essential in many types of spaces. Recent developments such as electronic acoustics systems can fulfill the promise of a true multipurpose room, but these systems work well only if they have an appropriately neutral backdrop for the "color" they provide.
Professional acousticians—such as members of the National Council of Acoustical Consultants—and acoustical standards (such as ANSI S12.60-2002) provide guidance in creating environments that have appropriate acoustics. They enable technology systems to work with the acoustical background rather than fighting it.
Richard Schrag (firstname.lastname@example.org) is a principal at Russ Berger Design Group, an Addison, TX-based design and consulting firm that combines expertise in acoustics, architecture, and interiors to create technical environments and buildings for recording studios, broadcast facilities, creative production spaces, and home theaters.
1 cf. Hu, Winnie. "In a Time of Distracted Ears, Teachers Ensure They're Loud and Clear." New York Times 16 March 2008