About | 22.06.2021 | By paul_simpson

BATOD members’ questions about improving acoustics and on speech discrimination

My classroom is not a new build; how can I argue to improve the acoustics?

 There are requirements for ’substantially’ refurbished learning spaces, but they are sadly a little lower in specification than new builds.  But what about a general classroom in an established school?

How to argue to improve existing conditions:

The important thing to discuss with educational settings is that all classrooms must be ’suitable’ for learning [NB suitable is NOT legally defined in the School Premises Regulations and Independent School Standards).

https://www.gov.uk/government/publications/standards-for-school-premises https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/800615/Independent_School_Standards-_Guidance_070519.pdf

BUT the most important area to argue for suitable acoustics, eg ‘access to (spoken) information will be duties under the Equality Act.

From ISS Part 5

‘although the production of an accessibility plan is not part of the requirements of the independent school standards, it should be noted that there is a requirement for such a plan to be prepared, published, reviewed, revised and implemented by the proprietor of an independent school under paragraph 3 of Schedule 10 to the Equality Act 2010’

https://www.gov.uk/guidance/notes-on-acoustics-lighting-and-ventilation-in-schools

 NB If a school plans to use a portable cabin style temporary structure as a classroom for more than 28 days, then the 2015 version of BB93 (quoted below) says that School Premises Regulation and Approved document E apply, i.e. the minimum standards for refurbishment and conversion of existing buildings apply.

0.3.2. Temporary buildings 

‘Buildings that are in place for 28 days or less are exempt from the Building Regulations including Requirement E4 but not from the School Premises Regulations and the Independent School Standards. New school buildings and extensions with a site life of more than 28 days should comply with all applicable Building Regulations including Requirement E4. Many buildings in schools have only temporary planning permission, which usually lasts for 2 years. These buildings are subject to the Building Regulations.’

‘Additional guidance on prefabricated buildings is given in Clause 0.6 of Approved Document E. Prefabricated buildings include, for example, a building created by dismantling, transporting and re-erecting sub-assemblies on the same premises or another premises. In these circumstances by virtue of the School Premises Regulations, the minimum standards for refurbishment and conversion of existing buildings apply.

Do we need a minimum of 80% in speech discrimination assessments to be able to make sense of what we hear?

80% is mentioned in the original BATOD Audiology Refreshers ( an update is in process) but I think this figure may be linked to 83% audibility (+10dB SNR) and we can say that deaf children need greater audibility due to fewer language experiences.  But we should consider that the speech signal is highly redundant and good levels of speech perception can be attainable with less than full access.

For example, (although the listener still has to make sense of what is audible),“Perfectly clear hearing for speech may be defined as audibility of all the useful information in the acoustic speech signal. In other words, clear hearing is achieved when 100 percent of the information in the sound leaving the talker’s mouth is present in the sound arriving at the listener’s ear… Perfectly clear hearing is difficult to achieve… Noise obscures, or masks, some of the speech sounds, thereby reducing audibility. To avoid this, the average level of the speech needs to be at least 15 dB above that of the noise”.(Smaldino and Flexer, 2012).

The amplitude of the softest speech sounds (weak consonants) to the loudest (strong vowels) varies by 30dB, or 15dB either side of an average level, so the listener needs at least +15dB signal to noise ratio (SNR) to have access to the range of speech sounds.

It is generally assumed that adults can function adequately when only around 50 percent of the useful information in the speech sounds is available. For example, adequate benefit from acoustic hearing aids is defined for adults as a phoneme score of 50% or greater on the Arthur Boothroyd word test presented at 70 dBA (NICE, 2019). But again, this requires that the listener “takes full advantage of their mature knowledge and processing skills, and the listener may expend considerable mental effort in making up for the missing acoustic information” (ibid).

When the levels of the speech and the noise are the same, the speech-to-noise ratio (SNR) is 0dB, giving 50% audibility of the useful information in the speech signal.  There is a relationship between audibility and SNR.  (NB see Boothroyd (2004) – speech intelligibility and speech audibility are different things but they are linked.)

 

Audibility SNR
50% 0dB SNR
58% 2.5dB SNR
67% 5dB SNR
75% 7.5dB SNR
83% 10dB SNR
92% 12.5dB SNR
100% 15dB SNR

As speech sound travels away from the talker it loses 6 dB of amplitude for every doubling of distance – the inverse square law or 6 dB rule. However, in a room there is a point where the sound source and the reflected sounds are equal in intensity, but beyond this critical distance reflected sound dominates.  So, in real life and without amplification, audible information is limited.

References

Boothroyd, A. (2004) Room Acoustics and Speech Perception. Seminars in Hearing, 25(02), 155-166. https://doi.org/10.1055/s-2004-828666.

DfE. (2015). Acoustic design of schools: performance standards (BB93). UK Government, the Department for Education. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/400784/BB93_February_2015.pdf

NICE (2019) Cochlear implants for children and adults with severe to profound deafness Technology appraisal guidance [TA566].

https://www.nice.org.uk/guidance/ta566/chapter/1-Recommendations

Smaldino, J. J., & Flexer, C. A. (2012). Handbook of acoustic accessibility: best practices for listening, learning, and literacy in the classroom. New York: Thieme.