From the Baltimore Sun
Copyright © 2006, The Baltimore SunThere were some misleading quotes and omission of some key facts about classroom acoustics in the above article that prompted ECH to respond with the following letter.
In reference to your 3/13 article entitled, "Volume rises in debate on classroom acoustics" I would like to respond to some statements. First, you cannot compare installation of a sound enhancement system (SES) in a classroom to increased volume in a sports arena or train station. The purpose of a classroom SES is to help children (whose auditory capabilities are not as developed as adults) detect, discriminate and comprehend sounds for the purpose of learning. This is the basis behind phonics and literacy which lead to higher level learning. Most importantly, you MUST understand that a SES is only SLIGHTLY increasing the volume of the teacher's voice. The main benefit is that the sound is equally distributed around the room, giving every child an equal opportunity to hear and learn.
The readers must understand that children with normal hearing need the teacher's voice to be 15 decibels louder than the noise in the room in order for that speech to be intelligible. (As mentioned in your article, this is 9 decibels louder than an adult would require.) This is the most critical component of acoustics, and it is referred to as the SNR or Signal to Noise Ratio. They must also understand that direct speech (the teacher's voice) drops 6 decibels for every doubling of distance. So a teacher speaking at 65 decibels 3 feet in the front of the room will be heard at 53 decibels 12 feet from the front wall, and so on. (See diagram) Yet noise, remains fairly constant around the room. These two factors explain why children not seated close to the teacher miss out on information (up to one third of the information.)
The acousticians recommend making acoustical modifications to the classroom to cut down on reverberation and background noise. The problem with this theory alone is that all the acoustical modifications possible will not correct the problem of the teacher's voice dropping over distance, and thus they ignore the required SNR of children. In fact, the ANSI standards that the MSDE recommends specifically exclude SNR from the scope of its standards. (See our FAQs page for details on this.) This is because ONLY a SES with speakers evenly distributing the sound can ensure that ALL children in ALL areas of the classroom will hear the teacher's voice at the SNR of +15 decibels. These same standards recommend a background level of noise in an UNOCCUPIED classroom, ignoring the reality of student occupied classroom noise.
It would be ideal to make all of the acoustical modifications AND install a sound enhancement system. But, it would not be cost effective. Acoustical modifications run well in excess of the $1700 cost of a SES, and ALONE cannot achieve the desired results. I am not aware of any studies which show the benefits from making just acoustical modifications to buildings. However, I have read the 50 plus studies that have been done showing improved academic performance, improved behavior, improved classroom management, improved literacy, reduced teacher absenteeism, high ROI, and reduced special education referrals from using Sound Enhancement Systems. This research supports this small investment in our children's education. A summary of these studies as well as many other important facts can be found at www.classroomhearing.org.
ECH Executive Director