Sound absorption is the loss of sound energy when sound waves comes into contact with an absorbent material such as ceilings, walls, floors and other objects, as a result of which, the sound is not reflected back into the space.
Sound absorbent materials can be used to create a suitable acoustic environment within a space by reducing the ‘reverberation time’. Reverberation affects the way a space 'sounds'. A long reverberation time can make a room sound loud and noisy and causes speech to sound muffled and muddy. Rooms designed for speech therefore typically have a short reverberation time of less than 1 second. Conversely, a longer reverberation time can enhance a music hall by adding richness, depth and warmth to music.
- Sports halls.
- Recording studios.
- Lecture theatres.
- Concert venues, cinemas and theatres.
Generally, sound absorption is applied in the form of treatment to floors, walls, ceilings, partition surfaces and objects such as chairs or bookshelves. The use of sound absorbing screens is also becoming more common.
Sound absorbers can be divided into three main categories:
- Porous absorbents.
- Resonance absorbents.
- Single absorbents.
Porous absorbents conventionally take two forms; fibrous materials or open-celled foam. Fibrous materials absorb sound as sound waves force the fibres to bend and this bending of the fibres generates heat. The conversion of acoustic energy into heat energy results in the sound effectively being absorbed. In the case of open-celled foam, the air movement resulting from sound waves pushes air particles through the narrow passages which in turn generate a viscous loss along with heat.
Usually a materials thickness has the greatest impact on its sound absorbing qualities. The thickness of materials can be compensated for with air space behind a wall panel or acoustic ceiling to improve performance at lower frequencies.
It is generally better to not include an airtight layer on the surface, such as a vapour barrier or paint layer, as this may reduce the sound absorbing qualities. However, architecturally, fibrous materials and open celled foams are not always considered attractive or robust. It is common therefore to cover these materials with an acoustically transparent finish such as a tissue, cloth or slatted wood, or with perforated materials such as wood, metal, plasterboard and so on.
Resonance absorbents consist of a mechanical or acoustic oscillation system, such as membrane absorbers, where there is a solid plate with a tight air space behind. Absorption reaches its maximum at the resonance frequency. The cavity can be filled with a porous material, to broaden the absorption over the range of frequency.
Single absorbers can be tables, chairs or other objects.
The sound absorbing characteristics of acoustical materials varies significantly with frequency. Low frequency sounds, below 500 Hz, tend to be more difficult to absorb whereas high frequencies sounds, above 500 Hz, are easier to absorb.
NB: Sound absorption is not the same as sound insulation which is used to prevent sound travelling between separate spaces across a partition such as a wall, ceiling or floor. Sound absorbing materials can convert some of the absorbed sound energy into heat, rather than transmitting it, which improve sound insulation, but it should not be seen as a substitute for adequate sound insulation.
 Related articles on Designing Buildings Wiki
- Acoustics in the workplace.
- Airborne sound.
- Ash deafening.
- Audio frequency.
- Building acoustics.
- Building Bulletin 93: acoustic design of schools.
- Impact sound.
- Noise nuisance.
- Pre-completion sound testing.
- Reverberation time.
- Robust details certification scheme.
- Room acoustics.
- Sound absorption coefficient.
- Sound insulation.
- Sound reduction index (SRI).
- Sound v noise.
- Structure-borne sound.
- UKAS accreditation for sound absorption testing.
The 2021 edition of the Building Conservation Directory, also available online, has been published. Find skilled trades specialising in work to historic and traditional buildings.
BT has revealed that almost 4,000 of its iconic red phone boxes across the UK are available for local communities to adopt for just £1.
On 26 March the IHBC, led by Prof. John Edwards, hosted a free one-hour CPD webinar ‘Introduction to Building Survey for Retrofit’ for sector professionals.
Greg Clark, writing an opinion piece for RICS, explores how good governance in cities pays dividends.
The Architectural Heritage Fund has issued a report on the first year of its ‘Transforming Places Through Heritage’ grants programme, funded by DCMS.
Europe’s star cities are scattered all over Europe but their perfect geometrical beauty can only be fully admired when seen from above.
The freely available Insight 1 series targets a wide range of cohorts who wish to gain an appreciation of practical heritage conservation.
The restoration and renewal of the Palace of Westminster is of ‘paramount importance’ according to the recent strategic review.
The IHBC's monthly CPD Circular showcases upcoming Events, Awards, Placements, Bursaries & Scholarships, Calls for Papers and more from across the UK and beyond.
The move of a 139 year old Victorian House through the streets of San Francisco drew an excited crowd of onlookers who came out to watch a truck slowly and carefully pull the historic house through the streets.