Matthew Bysouth
Educational Audiologist
Gathering evidence in support of
improving the acoustic conditions of
classrooms
Background
• Importance of acoustics in education
• Children as vulnerable listeners
• The effect of additional needs
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
• Materials are rated according to the amount of sound
they absorb and the amount they reflect.
• Measuring reverberation - BATOD recommends not
greater than 0.4 secs
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
Speakers for speech
signal/noise
Computerised speech test
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
Ear level microphones
Personal FM system
• 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
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
Matthew Bysouth
Educational Audiologist
The End
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.