Theme ‘noise and acousics’

‘Noise and acoustics’ is a theme in the chapters ‘architectural spaces’ and ‘interior design’ and is mainly in schools. (See the recommendations and for the literature en some technical remarks here.)

All students/pupils are subject to three sources of sound: from outside, from installations and appliances such as air systems en from teachers and other children. In the majority of Western schools, including the U.S., Canada and Britain the combined noise level is alarmingly high. Quite a proportion of students is troubled by this. One US-source says: “On any given school day, thousands of students across the country are unable to understand 25 to 30 percent of what’s said in their classroom. The reason: excessive noise and reverberation…” (See here for sources and some technical details about noise in school.)
If this is true for all students, one can only guess how many autistic students who are oversensitive to noise are affected and to what extent.
Sound from outside differs from school to school, depending on their location (highways, factories) and also on their soundproofing measures and acoustics. Extensive German research proves it’s quite possible to attain silent classrooms through noise reduction and reverberation measures.

British research shows that even the quietest classroom situations exceed the standard for background noise; in the noisiest situations even by 50%.
Representative research in 120 classrooms of 60 Dutch elementary schools shows that air systems in empty classrooms exceed the international noise standard of 35 decibels in 47% of the cases.

The biggest problem lies in noise produced by pupils and teachers themselves, a fact which underscores the paramount importance of the acoustic qualities of classrooms – see below.

The German research just mentioned, quotes a study which finds that 81% of the teachers agree with the statement “the noise of pupils causes me stress.”

The aforementioned British study distinguished six activity levels, ranging from ‘silent reading’ to ‘working in groups, moving around the classroom, with some talking’. In the most silent situation the noise level was 56 decibels and in three out of six exceeded 72 and 77 respectively. In order to understand speech in those situations the teacher would have to raise her voice to between at least 82 and 92 decibels (plus 15 dB). This is a higher noise level than that of a Diesel truck, passing at 30 feet. Most probably the 142 London schools included is this study (in areas away from flight paths into major airports) don’t compare badly with schools in any other European or North-American urban area.

According to the Health Council of the Netherlands “Noise levels exceeding 35 dB(A) can lead to reduced ‘speech intelligibility’ in classrooms and therefore interfere with the transfer and processing of information. This especially applies to sensitive groups, such as pupils and teachers with hearing problems and pupils with language difficulties, for example those with a different mother tongue. The Committee points out here that the noise produced by pupils will almost always exceed a noise level of 35 dB(A).”

No doubt many pupils on the spectrum can be included in these ‘sensitive groups’, so noise in the classroom poses a very serious problem to them.
About the sound conditions in schools for special education, we haven’t found specific information. To the extent class sizes are lower there, we may assume these conditions are comparatively better. According to the cited British study a class with 30 pupils creates twice the noise a class with 18 pupils does. This is also an argument for smaller classes in general.

Reverberation is expressed in the elapsed time between switching off a sound source and the moment the sound level is lowered to 60 dB. Reverberation time is a measure for the level of sound absorption of a space. (Some of the literature used here and some specifics on sound can be found here.)

Reverberation is an aspect of ambient noise, i.e. sound which echoes and persists longer in rooms called ‘noise spaces’.
An architect with long experience in this field says:
“Reverberation time can be a nuisance. A space shouldn’t be acoustically dry; that is unpleasant. Noise can be muted by way of ceilings, walls and floors with acoustic materials. Also materials used in interior design contributes to its absorption; thick curtains instead of luxaflex and upholstered.”

A special reason for avoiding ‘acoustically dry spaces’ or to take counter-measures once they are there, is that reverberation contributes to confusion about the source of sounds. People on the spectrum often have a lot more trouble identifying them and consequently are more confused than others. Such confusion adds to the nuisance; one can even say that the difference between sound and noise is marked by such confusion.

Let’s quote a father about his autistic son by way of illustration:
“A sound from cupboard doors, for instance, or from a hard floor, a passing train, a humming refrigerator, scooters, for him they are the wrong stimuli. Suddenly a sound builds up and he can’t tell what they are or where they come from; he cannot explain why there’s sound.”

This quote mentions virtually every way sound can trouble people with autism. The focus is on sounds from cupboard doors and hard floor surfaces. That is, on what are called ‘acoustically dry spaces’ in which the reverberation time is long.

In schools
The most important source of noise in schools are generally the pupils/students and teachers themselves. (See here.) Apart from drastic class size reduction, the most effective way of dealing with noise in classrooms is improving their acoustics. The positive effects on the number of quiet class hours and work-related stress of teachers has been proven in research.

Seven measures
There is a number of measures available against noise in school. One can be taken by students and/or their parents, which is to avoid schools with high noise levels. Think of location, class size and measures taken by schools. Briefly:
Limiting noise levels is an even greater must when there are students on the spectrum in the school.
Measures against reverberation deserve a very high priority.
Noise produced by installation such as air systems has to be limited. Make sure students understand the source and character of the noise they experience.
Create possibilities to escape unbearable noise levels, preferably by making low-noise spaces available.
Students/pupils who are unbearably affected by noise should be allowed to make use of head-phones and similar devices to neutralize and/or drown it out (i.e. with one’s own music).
A practical measure is to seat children who have trouble understanding their teachers close to them.


*Health Council of the Netherlands

Indoor air quality in primary schools. And the value of carbon dioxide as an indicator of air quality. The Hague, 2010. To be downloaded(download here).
Oberdörster, Markus en Gerhart Tiesler, Akoestiek in Moderne Onderwijsgebouwen. Over pedagogische trends, ruimte akoestiek, gezondheid leraren en gedrag leerlingen, Bremen, Universiteit van Bremen, Instituut voor interdisciplinair onderwijsonderzoek, 2006. PDF