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 1. It is now well established that the acoustic conditions of a physical space play a vital part in whether anyone in that space can learn and develop successfully. 2. Children, as both immature listeners and language users, are particularly susceptible to the affects of the acoustics of a physical space. We also know that a hearing impairment, language processing difficulty, learning difficulty or any attention difficulty inevitably creates a deficit in listening. The fact that these conditions can co-exist in a variety of ways only complicates the picture for any given child. 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? We can try to quantify these difficulties by examining in detail both the functioning of any given child and the acoustics of the spaces in which s/he is expected to learn. Whenever someone is LISTENING they are required to give particular attention to a given SIGNAL. In a classroom the signal is often the teacher or a teaching assistant speaking. It can, of course, be other young people or even media, such as, the sound from an electronic whiteboard. The integrity of this signal when it reaches the listener is determined by the acoustic properties of the physical space. Where the signal becomes degraded it is usually as the result of NOISE or REVERBERATION. The affect of NOISE & REVERBERATION

Acoustic Measurements - some terms and concepts Terms for a varied audience Short time slot In the next few slides I will be discussing acoustics . I’m aware that we have a very varied audience and for some these issues are ‘bread & butter’ but that for some the concepts being discussed will be unfamiliar. Please bear this in mind as we examine some of these concepts in a little detail. This is but a short time slot and I’ve necessarily not got too into the detail but tried to cover the important concepts in a general way.

Noise What is noise? How do we measure noise? Noise - Noise is any unwanted sound that may MASK the signal in some way. Noise can be generated by external sources (e.g. roads, other classrooms etc...) or by internal sources, such as, a media projector or heating system. Measurement - Noise levels in a room can be measured using a SOUND LEVEL METER. These measurements can be taken over any representative period of time. These measurements are usually reported as ‘dB A’. Typical conversational speech is delivered at around 60 dB A to a listener 1 metre away. BATOD recommends that noise levels recorded in an empty classroom with otherwise typical school activities taking place and with equipment switched on, windows open etc... should be below 35 dB A for rooms in which deaf children are taught. BATOD recommends not greater than 35 dB A

Reverberation What is reverberation? How does reverberation affect a signal? Reverberation - This is the effect of the physical environment upon the sound within it. Materials absorb and reflect sound in different ways depending upon their construction and placement in the room. The sound that we hear is a combination of the direct sound from the listener and the sound that is reflected from the walls, floor, ceiling, windows and other surfaces in the room. As the amount of reflected sound increases in relation to direct sound, the signal can become smeared and indistinct making speech harder to understand.

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 Materials are rated according to the amount of sound they absorb and the amount they reflect and these ratings can be used to make judgements about the reverberant qualities of a material. Measurement - Sound analysis equipment can be used to measure the reverberation of a space. A signal is generated and the measuring device calculates the reverberation for given frequencies. This is typically reported in ‘secs’ - BATOD suggests that rooms where deaf children are taught should not have reverberation times above 0.4 secs across most frequencies.

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. Noise measurements and reverberation measurements are usually combined with detailed information regarding the built materials and the dimensions of the room to produce an acoustic report. The author will make recommendations regarding any acoustic adaptations to the room required by referring to published data regarding optimal listening conditions and how to achieve them. 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. 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 However, there is an important aspect missing from the data collection and report writing as described - the young person/people. You have not yet collected data that will help you understand the specific listening experience of the person you are trying to help.

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 See slide and then.... in order to determine these needs it is necessary to use a method that enables the TEACHER OF THE DEAF (TOD) to determine the SIGNAL TO NOISE RATIO (SNR) that a young person needs to listen to their best ability. By comparing this with the actual SNR in the classroom the TOD can determine whether your classroom requires acoustic adaptation even if it meets some of the published criteria for noise and reverberation levels. How?

Sound Assurance - a practical method Sound Assurance by Tony Shaw SPEECH IN NOISE TESTING (SPIN) SPIN methods The method described here is called Sound Assurance and was devised by Tony Shaw. The first stage of this method involves determining the SNR that is required by the young listener. This can be done by the TOD by conducting SPEECH IN NOISE TESTING (SPIN). SPIN is conducted by using recognised age appropriate speech discrimination tests. The speech is played through a loudspeaker or computer display (to enable lip-reading) and classroom noise can be played through other speakers at various points in the room. By adjusting the level of the signal (speech) and the noise the SNR where the best score is achieved can be carefully measured. Determining required SNR

Speakers for speech signal/noise Computerised speech test SPIN TESTING Speakers for speech signal/noise Labelled Picture and recordings of SPIN TESTING 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% SPIN testing results in an optimum SNR expressed as a positive number, e.g. +25 dB. +25 dB SNR would mean that the child requires the signal to be 25 dB louder than any noise if s/he is to achieve their optimum score in the speech discrimination testing. Note that optimum is not necessarily 100% correct but the best they can score. The effect of different SNR can also be measured so that when the classroom sound is measured a good estimate can be given regarding the amount of information the young person can discriminate accurately in probably less favourable conditions. Recording scores with different SNR can be informative for reporting

Making Class Recordings Digital audio recorder Ear level microphones Personal FM system Knowing the required SNR by the child allows the TOD to measure the class noise and compare. Knowing the required SNR by the child allows the TOD to measure the class noise and compare. This is achieved using a digital portable recorder and either one or two ear level microphones. This relatively discreet equipment is worn by the young person throughout a series of commonplace activities and allows the sound at the child’s ears to be recorded. The recorded sound captures the effect of any ambient noise alongside the reverberation qualities of the room materials in a single recording. 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. It is also possible to record the sound from a soundfield system or personal FM system alongside the sound in the classroom in order to compare SNR with and without soundfield/personal FM - assuming it is the signal and not the noise! - Teacher forgets to mute or switch off etc...

Making Class Recordings Sound Assurance testing in class Labelled Picture and recordings of CLASSROOM RECORDINGS This method is ‘recording’ the the acoustic parameters that were measured in the previous methods - the effect of noise and reverberation on the signal is included in the recording. It is all encompassing as it records the environment in which the auditory event takes place.

Interrogating Recordings The classroom recordings are transferred to a computer running some digital audio editing software, eg Adobe Audition What is audio editing software? The classroom recordings are transferred to a computer running some digital audio editing software, e.g. Adobe Audition. Audio editing software is designed to be used by the broadcast and music industry and always contains a number of useful tools. Firstly, the recordings can be ‘cut’ and sections re/moved in order to get snippets of representative ‘samples’ of the various recorded activities. What is specifically required is examples of ‘moments’ where the signal (e.g. teacher speaking) is recorded near a moment of just noise - this allows the two moments to be compared. Find the right moment on the recordings

Interrogating Recordings Waveform view (can show spectrograms) Where the analysis is shown Labelled Picture and recordings of Adobe Audition working

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 Using the analysis function of the software it is relatively straightforward to derive accurate SNR for any particular moment in time for one particular position in the room (where the child wearing the recording equipment was placed). This figure can be compared with the required SNR measured during the SPIN. Using this method it is possible to derive SNR for as many types of listening activities as take place - e.g. teacher talking to class or to child specifically, child to child speech, small group work etc...

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. It is also possible to compare the SNR ratio achieved through conventional un-amplified speech and the effect of adding a soundfield system or a personal FM system. Thus, alongside the conventional acoustic audit mentioned at the beginning of this talk, Sound Assurance allows the TOD, SENCo and class teacher to make accurate statements about the actual listening experience for an individual child. If the SNR achieved in the classroom is shown to be below the SNR required by the SPIN testing concern should be raised as it shows the young person will inevitably not be achieving their optimal speech discrimination during these activities. 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 Taking measurements with a soundfield system and/or personal FM system alongside conventional measurements of noise and reverberation allows for accurate predictions to be made about the effect on the child’s listening experience of adapting or augmenting the acoustic conditions of the space........can the SNR be improved and how? This makes these measurements ideal as evidence when requesting improvement to the learning environment through either physical adaptation or the fitting of a soundfield system and/or personal FM system.

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.