ACOUSTICS TAKE THE LEAD IN CLASSROOM DESIGN
- By Ellen Kollie
- February 1st, 2006
"Acoustics often get overlooked because you can't see it," says Pamela Marchesano, general manager of Alexandria, Va.-based Novawall Systems, Inc. "People don't think about it when building. When a teacher moves into a new classroom and finds poor acoustics, it's too late."
Fortunately, with today's focus on sustainability and ADA, more attention is being given to classroom acoustics. In fact, in 2002, ANSI Standard 12.60 for classroom acoustics was published. This standard is now leading classroom design as administrators, designers and architects strive to create excellent learning environments.
The first draft of the standard was written in large part by Kenneth Roy, Ph.D., a senior principal research scientist with Armstrong in Lancaster, Pa., while participating in a work group organized by Acoustical Society of America He says that there are basically two types of standards.
The first is a prescriptive standard, which says that, if you build using certain wall and ceiling constructions and use certain HVAC equipment, etc., then you can assume you'll meet the target acoustic performance criteria. This type of standard usually allows an architect to adequately design a space without additional input, but usually at added cost per classroom since multiple "safety factors" are not included.
The second is a performance standard, which doesn't tell designers and architects how to design, but rather what the design needs to meet in terms of acoustic performance criteria. This type of standard usually requires the services of an acoustical consultant, but there should be a cost savings per classroom since the design is specific and not dependent on multiple "safety factors" as the other approach. Roy says ANSI Standard 12.60 is primarily a performance standard, but with extensive appendices containing design information and prescriptive elements to aid in the design process.
Three factors affect the architectural acoustic performance of a space, says Roy. They are the size of the room, the shape of the room and the type of surfaces in the room.
Once you've chosen those three factors, you've determined the room acoustics.
The two things that combine to determine what level of speech intelligibility a classroom has are reverberation time and background noise. For example, if spoken words float around for a long time, then the reverberation time is too long and intelligibility is impeded. Likewise, if an HVAC system is so noisy that a teacher can barely be heard over it, then background noise is too loud and intelligibility is again impeded.
Reverberation time and, to a lesser extent, background noise are determined by the first three factors: room size, shape and surfaces.
Those are issues related to acoustics within a room. Another issue to consider when dealing with architectural acoustics is transfer of noise into the room from outside.
Let's put this information into action. If you have a classroom that measures a standard 30 ft. by 30 ft by 10 ft., installing a good acoustic ceiling (which is an inexpensive way to achieve good acoustics) and with a 0.70 NRC (Noise Reduction Coefficient), puts you in good shape, says Roy. This should put you with a reverberation time of 0.60 seconds, which is the standard for a room less than 10,000 cubic ft. And it should help to give you a background noise of not more than 35 dBA, which is the standard for rooms up to 20,000 ft., if a properly designed central HVAC system is installed.
"But, as the room gets bigger, you have to think, 'What else can I do?'" says Roy. Let's say you have a lecture-type classroom that's bigger than 20,000 cubic feet and a ceiling that is 12 ft to 15 ft. high. Now sound will bounce off the walls and take a long time to hit the ceiling, which translates to a high reverberation time. (The standard reverberation time for rooms from 10,000 cubic ft. to 20,000 cubic ft. is 0.70 seconds. Guidelines are given in the appendices for school spaces larger than 20,000 cubic ft.)
To solve this challenge, you have to add sound absorption to the walls as well as the ceiling, which should give a reasonable reverberation time and help to achieve a 40 dBA background noise (the standard for classrooms greater than 20,000 cubic ft.). In fact, as a rule of thumb, anytime you have a ceiling greater than 15 ft. high, you have to use sound absorption on the walls. "Typically, sound absorption applied to the walls is more expensive than on the ceiling," Roy points out. "You'd rather not do it unless you have to."
"It's a balance," offers Marchesano. She notes that too much sound absorption is as poor as not enough and that it's important to focus on the area from 2 1/2 ft. to 7 ft. vertically. That's where the teacher is speaking, so that's where sound is hitting the walls.
A Standard for Everyone
"The standard is only 10 pages long, but the appendix is 26 pages long," Roy says. "It tells how to do things, so architects have options." He also notes that, because not everyone can afford to hire an acoustical consultant, you can hopefully use the appendix to achieve success on your own.
Roy stresses that ANSI is a voluntary standard. At this point, a number of states, including Ohio, New Hampshire, New Jersey, Minnesota and Connecticut have adopted it. Other classroom acoustics standards/directives based on ANSI S12.60 are in use in the states of California, Washington and New York as well as in the Los Angeles, Philadelphia, Minneapolis and Washington, DC, school districts. Even if your state doesn't require it, your school district can specify in construction documents that it be used. "The standard can have a positive impact," he sums, "and it's starting to."
Marchesano adds that good acoustics can easily be accomplished when planning new construction or renovation, and it doesn't have to be expensive. It keeps the classroom as a whole more comfortable, and keeps young minds open to learning.