A simple method to reduce built-up noise in schools - CSP Acoustics

A simple method to reduce built-up noise in schools

Last July, Clackmannanshire Council invited us to provide design guidance to address excessive noise in the multi-function hall of Strathdevon Primary School. Recently, we heard that our design advice has been incorporated in the refurbishment and the school is very happy with the results, though the method is simple and easy.

The story began with a new pupil with special needs arriving at the school last year. He has cochlear implants and a form of autism. He could not bear the noise in the multi-function hall, but this hall was frequently used for many types of activities, such as PE lessons, whole school assembly, breakfast club, lunch sittings and occasional performances. Once he entered the hall, he felt so distressed that he would “pull his ears off”, especially during PE lessons and lunch sittings. He had not been able to attend a whole school assembly in the hall.

Clackmannanshire Council and the school decided to refurbish the hall to improve the acoustic environment.

The hall was naturally ventilated and heated by electric radiators. As a result, no discernible mechanical noise was present in the hall. The high level of noise in the hall was mainly due to the build-up of reverberant sound coming from teachers and pupils.

The hall occupied 167m2 floor area with a volume of 870m3. We carried out reverberation time measurements in the hall before the refurbishment and the result at middle frequencies was 1.8 seconds; exceeding the higher limit required in the current national standards for schools Building Bulletin 93 (BB93).  BB93 requires that the reverberation time in a multi-function hall should range from 0.8 seconds to 1.5 seconds for refurbishment.

It was clear that the hall needed additional absorptive material to reduce the reverberation time and thus reduce the built-up reverberant noise. Most areas of the two side surfaces of the hall were external windows. If adopting ordinary absorptive curtains, natural light would be blocked. The wall surfaces at the middle level were covered by radiators, which were not suitable for installing absorptive panels. The rest of the walls were used for posters, which were not suitable for installing absorptive panels either.

We identified that a transparent absorptive curtain product was available on the market. When it is installed at 0.15m from windows and folded at 100% fullness, the laboratory tested absorption performance can reach 0.5 at middle frequencies (which means the curtains can absorb 50% of the sound energy incident on them).

We recommended that all the existing PVC blinds be replaced by the transparent absorptive curtains, with additional absorptive panels on the ceiling. Installing curtains is simple and easy, while installing absorptive panels on the ceiling is more complicated and costly, and it would also have an impact on the appearance of the hall. The school decided to install the curtains only.

To everyone’s surprise, after adopting such a simple and easy method, the teachers and the pupils in the school found that the acoustic environment in the hall has been improved considerably, the reverberant noise being reduced significantly. The improvement certainly helps the pupil with special needs settle better there.

The curtain suppliers were delighted when they heard this news and invited us to return to the hall, to re-measure the reverberation times. The test results confirmed our clients’ subjective feelings. The reverberation time at middle frequencies has been reduced from 1.8 seconds to 1.3 seconds, complying with the criteria set out in BB93.

In general, this simple method of sound absorption has achieved a satisfactory outcome.

Reverberation time test results before and after installing the transparent absorptive curtains


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