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Room Acoustic Design – Acoustic Masonry

The Impact of Acoustics in Schools
With new research into acoustics in schools it has become apparent that often classrooms have poor acoustics. As a result this can have a significant negative impact on the educational development of children. Whilst adults can make guesses at words missed, children often find it harder to do so.

Prior to 2003, Part E of the Building Regulations did not apply to schools. It now includes schools within its scope. Building Bulletin 93 aims to:

  • Provide a regulatory framework for the acoustic design of schools in support of the Building Regulations
  • Give supporting advice and recommendations for planning and design of schools.
  • Provide a comprehensive guide for those who are involved in the design of new or refurbished school buildings.

Performance standards are defined in BB93 for the following:

  • Indoor ambient noise levels from external sources and building services defined on a room classification basis
  • Airborne sound insulation between spaces
  • Impact sound insulation of floors
  • Reverberation within teaching and study spaces
  • Sound absorption requirements for corridors, stairwells and entrance halls
  • Speech intelligibility requirements in open plan spaces

Unfortunately classrooms throughout the UK and Ireland currently suffer from poor room acoustics. The problem can be eradicated at the source however with the use of a revolutionary Acoustic masonry block Alphacrete Acoustic.

The science behind poor acoustics.

Why are some rooms acoustically poor?
There are a number of factors to take into account when analysing the acoustics in any one room, the following play a major part in creating a poor acoustic environment.

  • Too much reverberation
  • Sound from other rooms penetrates the walls
  • Flutter echos

What is reverberation?
Reverberation is the persistence of a sound after its source has stopped, resulting in poor speech intelligibility in rooms.

  • The effect of reverberation on speech.
  • Decreases the overall understanding of speech
  • Vowels interrupt the understanding of lower loudness consonants. Vowels tend to be 10-15 dB louder than consonants.
  • Silent intervals between syllables, sounds and words are filled with reflective energy resulting in a smearing effect of the sound.

Ways to reduce reverberation time.
In order to reduce reverberation time, you need to increase the absorption in the room. Absorption can be increased by the replacing of covering hard surfaces with softer ones to minimise the amount of reflection.

Acoustic experts have already proven that Alphacrete Acoustic blocks offer significantly better acoustic absorption than alternative products that are typically employed in similar applications.

Acoustics in classrooms
Two important characteristics of an acoustically optimized classroom are a low background noise level and a low reverberation time. The background noise may be from adjacent classrooms or activity outside. Reverberation is the multiple reflections of sounds within a room that can prolong and distort the original sound components. Speech intelligibility is compromised when a soft vocal element is masked by the reflected sound of a preceding louder element. Reverberation also has the effect of amplifying background noises.

For optimum speech intelligibility a reverberation time of less than 0.6 or 0.8 seconds is required for classrooms.

Other applications for Alphacrete Acoustic
In addition to classrooms, poor Acoustics can have a significant impact on other rooms, and buildings depending on their applications.

Assembly halls.
The number of hard surfaces in a hall makes it an extremely ‘live’ environment as far as sound is concerned. As a result speech intelligibility often suffers in this environment. Assembly halls within schools in particular due to the variety of applications are often an acoustic challenge. Typical uses can range from drama, parents evenings, lectures, exam halls, sports use, audio / visual presentations. A room where a whisper can be heard as well as a school choir can prove challenging.

For optimum speech intelligibility a reverberation time of 0.8 to 1.2 seconds is required for assembly halls.

Sports halls.
Typically gymnasia sports halls are built to be robust. Sports halls require large volumes of space with excellent light and acoustics. in order for the users to enjoy their activities without distraction. The design of sports halls normally incorporates a number of hard surfaces to withstand use, unfortunately these combine to produce particularly poor acoustics.

Reverberation time of less than 1.5 seconds is required for sports halls.

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Music Rooms
Music rooms are one of the most challenging when it comes to acoustics, as music will produce more sound than any other type of lesson in a school. The design of the room itself should be considered, and parallel walls should be avoided if possible to reduce the occurrence of flutter echoes and standing waves.

Reverberation time of less than 1.0 seconds is required for music classrooms and less than 0.8 seconds for small practice / group rooms.

Conclusion
Alphacrete Acoustic effectively deals with room acoustic problems, by the absorption of the reverberant sounds. It achieves this through its unique geometry and mix design, and has been tested and accredited by sound research laboratories. All measurements of sound transmission were performed in accordance with the guidance set down in BS EN ISO 140: 1995: Acoustics — Measurement of sound insulation in buildings and of building elements, Part 3 — Laboratory measurement of airborne sound insulation of building elements. Alphacrete Acoustic offers excellent resistance to the transmission of airborne sound, and with a wide range of colours available enables specifiers to create stunning schemes which not only look good, but sound good too.

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