Page 33 - Fall 2005

ASA MEMBERS OF ANSI W/G S12.42
Robert E. Apfel
John S. Bradley Bennett M. Brooks Daniel C. Bruck Angelo J. Campanella Robert C. Coffeen
T. James DuBois Stanley L. Ehrlich John Erdreich Richard D. Godfrey William H. Hannon Robert D. Hellweg
Murray R. Hodgson K. Anthony Hoover Daniel L. Johnson Howard F. Kingsbury Jerry G. Lilly
Harold L. Merck Peggy B. Nelson Michael T. Nixon Stephen W. Payne, Jr. Karl S. Pearsons Richard J. Peppin Joseph Pope
Daniel Queen Stephen I. Roth Kennneth P. Roy Mark E. Schaffer
Neil T. Shade
Gary W. Siebein Joseph J. Smaldino Sigfrid D. Soli
Noral D. Stewart Brandon D. Tinianov Ewart A. Wetherill William A. Yost
Linn Redden Anne Seltz
Linda L. Semesky Donna L. Sorkin Sarah J. Woodhead
NON-ASA MEMBERS OF ANSI W/G S12.42
Karen L. Anderson Daniel Collings Carl C. Crandell Gary Ehrlich David Fagen
Jay J. C. Gould
Steve Inglis Cheryl D. Johnson John Lyons Ronald Moulder Julie Olson Richard Randall
initially recommended maximum background noise levels of 30 dBA, for example); some advocated for less. Nevertheless, we have learned that a number of countries have converged on the same background noise recom- mendation.
The working group also considered several possible standards for maximum reverberation time. Data from Nabelek and Nabelek (1985) and others suggest- ed the shorter the recommended RT60, the better for speech recognition. When the RT60 approaches .5 s or shorter, few detrimental effects on speech recogni- tion have been noted. When RT60 is very short, sound quality may decrease. The working group agreed that recom- mending a maximum RT60 of 0.6 s for unoccupied classrooms would almost certainly result in a lower RT for occu- pied rooms, once children and furniture were in place. That value also seemed
feasible to achieve in real rooms without extensive modifica- tion. Again, other organizations (such as ASHA) had recom- mended stricter or similar criteria.
The quest for good school acoustics seems to have picked up speed around the world. We know of acoustics standards in Sweden, Germany, the United Kingdom, Italy, Portugal, and Croatia. Some countries are farther along in their implementa- tion of an acoustics standard for schools. The United Kingdom has implemented a mandatory standard for new construction. The World Health Organization has compiled recommenda- tions for its European region. The word about children’s need for good acoustics seems to be spreading.
How much does it cost?
We recognize that building schools to meet this standard will not happen without some additional cost. To meet the acoustical needs of children, designers will need adequate par- titions, windows, and doors to control the sound levels of intruding noise from outside the classroom. Beyond that, the HVAC systems seem to present the greatest challenge. Manufacturers of central, ducted HVAC systems are currently meeting that challenge by offering quiet systems that will meet the standard. Estimates for the increased cost of including these high-quality doors and windows as well as central ducted HVAC systems have been between 1% and 3% of construction costs. The United Kingdom reports that it is able to build quiet schools for less than 1% additional cost. It seems a good trade- off for providing full acoustic access to all children. Additional information about costs can be found at www.quietclassrooms.org in the list of links below.
What’s next?
The standard has been making news. Efforts are under- way in several states to include the standard in future build- ing codes for new school construction. The U.S. Department
room noise. These special populations of children constitute a significant proportion of typical public school classrooms, and they should be a consideration in the acoustical design. Nevertheless, good acoustics are needed by all children.
What agreement do we have for the limits to back- ground noise and reverberation that children need?
The working group engaged in extensive discussion of the recommended performance standards. Guidance was sought from research, from other agencies concerned with hearing in children, and from other countries engaged in this dialogue. Based on the literature, children do not reach maximum performance for recognizing familiar speech in background noise at SNRs of +10 dB or less. A common finding amongst researchers was the need for +20 dB SNR. As we surveyed other organizations (such as the American Speech-Language-Hearing Association, or ASHA) and other countries’ standards (such as England, Sweden, and Croatia), we found a common desire for at least +15 dB SNR for children to achieve their maximum performance potential. One must consider the need for +15 dB SNR throughout a classroom, and the fact that the average sus- tainable comfortable conversational speech level of 65 dBA at one meter’s distance. Speech is a highly complex signal that varies in frequency and level quickly during conversa- tional speech. Even when one speaks at a relatively constant overall level, individual phonemes in a sentence vary in level by 30 to 40 dB. A sentence that is produced at an aver- age level of 65 dBA, then, may contain vowels that are as high as 75–80 dB and consonants as low as 45-50 dB. In addition, one must assume that voice levels decrease with increasing distance. With these assumptions, the perform- ance criterion of maximum noise levels of 35 dBA (55 dBC) was recommended. Other agencies had recommended more strict criteria (ASHA and the Swedish working group
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