As a speech room increases in size, it becomes more difficult to maintain speech intelligibility and more critical to optimize the acoustics of the space. It is necessary to view the area as a passive amplification system. Larger speech rooms naturally have lower signal-to-noise ratios because the average listener distance is greater and the speech signal has to travel farther. Therefore, speech rooms should be as small as practical for the intended capacity. The goal for the shape of the space is to minimize the average speaker-to-listener distance. This is why Greek amphitheaters are semi-circular. The ceiling should be as low as possible to limit the volume of the room and decrease the amount of acoustic treatments needed to control reverberance. This is why a number of good speech rooms are fan-shaped with very low ceilings.
Noise inside a speech room can potentially come from many different sources including those located on the exterior of the building, in other interior spaces, or the building systems themselves. The building envelope should be designed to attenuate the level of environmental noise specific to the site. Interior partitions around speech rooms should always be full height, extending from floor to floor or the roof above. Stopping the partitions at ceiling level and leaving an open plenum above adjacent rooms is not permitted by school design standards. Also it is neither recommended nor endorsed by professional acoustics or hearing organizations. The building’s mechanical, electrical, and plumbing (MEP) systems should operate quietly by locating noisy equipment remotely from speech rooms and routing ducts and piping around, and not over speech rooms.
The most important and often overlooked source of noise interfering with speech intelligibility is reverberation, or how long sound reflects around amongst the ceiling, walls, and floor surfaces. It is the most disturbing source of noise because, unlike a truck or airplane pass-by or someone laughing and talking as they walk down the hallway, reverberation is always present, interfering with every spoken word all day long. High-performing sound absorption should be positioned overhead and in taller rooms on the upper walls as well.
For a detailed set of performance criteria and guidelines, it is advisable to refer to the American National Standards Institute/Acoustical Society of America (ANSI/ASA) S12.60, Acoustical Performance Criteria, Design Requirements and Guidelines for Schools. The criteria in this standard also form the basis of the acoustical requirements in the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) v4 and the Collaborative for High Performance Schools (CHPS), Criteria for New Construction and Renovation. As a minimum, these standards require an acoustic ceiling with a noise reduction coefficient (NRC) of 0.70 to 0.75 or a reverberation time (RT) no longer than 0.60 seconds.
Even if the applicable school district does not require compliance with one or more of these standards, they can still serve as a basis of good acoustic design for any educational facility. Professional acoustics and hearing organizations, such as the ASA, the American Academy of Audiology (AAA), and American Speech Language Hearing Association (ASHA), endorse and recommend that all schools comply with the requirements in the standards mentioned above.
Rooms for focus
Many rooms in educational facilities are not used by groups for understanding speech or appreciating music. Instead, occupants must work independently, concentrate, focus, or relax. Examples include computer labs, administrative offices, study lounges, and media centers. In these focus rooms, speech needs to be attenuated, not amplified. When these spaces are excessively loud and reverberant, they are very stressful. Speech carries, and distracting noises negatively affect concentration, productivity, or decompression. The acoustic goals in these focus rooms can vary from quiet relaxation or contemplation in an area of respite to individual concentration in a niche of a library or computer lab.