Connevans equipment for deaf people

Room acoustics measurement

The acoustic properties of an enclosed space are typically described by:

1. the ambient noise level (usually as a function of frequency) in the space under normal usage conditions

2. the reverberation time

3. the insulation of the structure from airborne and impact noise from outside the space

Why do I need to know about acoustics in schools?

Ambient background noise affects speech intelligibility and the concentration of room occupants. Student and teacher performance is proven to be better in low ambient noise conditions.

Long reverberation times (typical in older school buildings) adversely affect speech intelligibility, especially at a distance from the source of sound (usually the teacher's voice).

Ambient noise and reverberation time are the most important parameters to know.

What am I going to use the information for?

If the purpose of quantifying room acoustics is to benchmark existing teaching spaces for timetabling of HI students or for budgeting of acoustic improvement measures, then indicative survey quality measurements will be adequate. If accurate room acoustics qualification is required in order to contest 'out of county' placement tribunals, challenges to 'fit for use' in new-build, or acoustic treatment of rooms with marginal survey results, then the measurements must be made in a much more rigorous way.

What is BB93?

BB93 is the Buildings Bulletin Issue 93. It is a government document that provides a regulatory framework for the acoustic design of schools in support of the Building Regulations. These regulations specify minimum acoustic performance requirements for teaching spaces, particularly in recognition of the requirements of the Special Educational Needs and Disability Act 2001 for integration of children with special needs in mainstream schools.

There are three options for assessing classroom reverberation time.

1) Theoretical calculation:
Purely mathematical from Sabine formula with no acoustic measurement taken. The Sabine formula is based upon a rectangular empty room with known surface absorption coefficients - this method is very time consuming and highly prone to error in a furnished room as it requires many careful size measurements and multiple subsequent calculations.

Theoretical calculation can be used at the building design stage but otherwise, in our view, is a waste of time and effort.

2) Classroom Reverb Survey Kit - Quick assessment survey:
Connevans offer a Classroom Reverb Survey Kit - at less than £500 the kit is affordable and easy to to use. The kit can measure reverberation - accuracy around +/- 10% with correction for room volume. The kit also provides a useful sound level meter which can measure 41-115dB SPL (A). Weight 4.7Kg (including all options)

Another Sound Level Meter such as the Cirrus 252B may be used to measure approximate ambient noise levels down to about 32dBA SPL (not many real classrooms are this quiet!) These measurements are indicative and are sufficiently realistic for practical use but the methods are not rigorous enough to be used as evidence in the support of BB93 claims/tribunal hearings.

Classroom Reverb Survey Kit information sheet

Classroom Reverb Survey Kit instructions

3) Accurate measurement of parameters:
Connevans offer a Room Acoustics Measurement Package - at around £6500. This package can accurately measure reverberation time, ambient noise and make sound level measurement to meet BB93 requirements including data logging, spectrum analysis and speech transmission index.

The Connevans Room Acoustics Measurement kit it is suitable for characterizing the acoustics of all typical school teaching spaces including halls and gymnasia and contains everything needed to make the measurements required to prove compliance with BB93. This kit can be used to provide satisfactory evidence for use in tribunals. For ease of use, comprehensive step by step instructions are given for making the required measurements.

This kit can measure the following parameters:

Ambient noise as a function of frequency down to 17dBA SPL
Data logging of ambient noise, LAeq, 10 secs to 99 hours.
Reverberation time (RT60) as a function of frequency up to 8 seconds
Speech Transmission Index (speech intelligibility)
Airborne sound insulation between spaces as a function of frequency (limited frequency & dynamic range if using portable speaker supplied with kit)

The standard kit does not measure Impact sound insulation (but this is not normally required)

The standard kit has two cases:

1) Handheld Type 1 (+/-0.5dB accuracy) integrating and data storing sound level meter with all necessary software applications. The meter may be used stand-alone and is supplied in a rugged carry case along with a calibrator, mains charger, PC upload cables, upload software and instructions. Weight 2.9Kg

2) Rugged wheeled trolley case containing amplified speakers, tripods, cables, impulse generation device (for quick surveying), ear defenders, CD player (for STI measurement), power supplies, mains extension lead, long range ultrasonic distance measure and PC software including the Connevans RTFIX reverberation time reduction & cost calculator. Weight 17.5Kg.

Impulse device and ear defenders may be carried separately for quick surveying so that the trolley case need not be moved around more than necessary (weight 1.4Kg)

Visit www.DeafEquipment.co.uk to order or to view details of any of the packages we offer online .

We offer our Room Acoustics Measurement Package for hire - please contact customer services if you would like details.

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