Matthew Bysouth Educational Audiologist

Gathering evidence in support of improving the acoustic

conditions of classrooms

• Children as vulnerable listeners

• The effect of additional needs

• Importance of acoustics in education

Background

Acoustic Measurements - some terms and

concepts

• The need to examine both the functioning of the child and the acoustics of the space

• What does LISTENING mean?

• The affect of NOISE & REVERBERATION

Acoustic Measurements - some terms and

concepts

• Terms for a varied audience

• Short time slot

Noise

• What is noise?

• How do we measure noise?• BATOD recommends not greater than 35 dB A

Reverberation

• What is reverberation?

• How does reverberation affect a signal?

Reverberation

• Measuring reverberation - BATOD recommends not greater than 0.4 secs

• Materials are rated according to the amount of sound they absorb and the amount they reflect.

Acoustic report

• Building/furnishing materials and room dimensions - referenced to published data

• Advice is usually concerned with reducing both the negative reverberant effects of reflective surfaces and the levels of ambient noise.

• This may require the installation of better quality acoustic absorption materials and/or the fitting of a soundfield system.

What is missing from this method?

• the listening experience of the young person or people

What is missing from this method?

• SIGNAL TO NOISE RATIO (SNR) - (the difference in intensity between the signal and the noise (expressed in terms of +/-) required by the young person

• Compare this with values recorded in the classroom. BATOD recommends that SNR should be greater than +20 dB up to 750 Hz and greater than 15 dB above this frequency

• How?

Sound Assurance - a practical method

• Sound Assurance by Tony Shaw

• SPEECH IN NOISE TESTING (SPIN)

• SPIN methods

• Determining required SNR

SPIN TESTING

Computerised speech test

Speakers for speech signal/noise

Personal FM system

Speech in Noise Testing (SPIN)

• SPIN testing results in the optimum SNR being expressed as a positive number, e.g. +25 dB

• SNR required for ‘best’ score - not necessarily 100%

• Recording scores with different SNR can be informative for reporting

Making Class Recordings

• Knowing the required SNR by the child allows the TOD to measure the class noise and compare.

• Method for making the recordings

• Recordings contain both signal and noise

Digital audio recorder

Personal FM system

Ear level microphones

Making Class Recordings

• Record the signal from a soundfield system and/or personal FM. When used properly this signal should be significantly better than that recorded without the soundfield and/or personal FM - assuming it is not unwanted noise.

Making Class Recordings

Sound Assurance testing in class

Interrogating Recordings

• The classroom recordings are transferred to a computer running some digital audio editing software, eg Adobe Audition

• What is audio editing software?

• Find the right moment on the recordings

Interrogating Recordings

Waveform view (can show spectrograms)

Where the analysis is shown

Interrogating Recordings

• Use analysis function to find SNR for each sample

• Compare with the required SNR measured during the SPIN

• Derive SNR in school for a variety of activities and interactions

Interrogating Recordings

• Compare the SNR ratio of un-amplified speech with soundfield and/or personal FM system.

• ToD, SENCo and class teacher can now discuss the actual listening experience of an individual child.

• What if optimum SNR is never achieved in class?

Recommendations and Evaluation

• Can SNR in class be improved?

• Use these measurements to make a good case for funding and equipment

The End

Matthew Bysouth Educational Audiologist

Further Reading

Shaw, Tony. Sound Assurance. Chapter 5 in Phonak VIP elearning Virtual Conference Proceedings, FM for Children. Phonak. Available from Phonak.

Carol Flexer. June 2011. Creating accessible classroom environments for listening and learning. Conference notes, Manchester 2011. Available to download from the internet as a PDF document.

NDCS. Acoustic Tookit. Available to download as a PDF document from the NDCS website.