Acoustic Advantages of Wool Carpeting
Steve McNeil
Technical Bulletin, 2014, AgResearch, Christchurch, New Zealand
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The acoustic properties of wool carpets provide benefits that should be considered
when choosing floorcoverings. At home, the noise reducing properties of carpets
provide comfort and at the office, they increase job satisfaction and performance.
Carpets control noise by reducing the floor noise, absorbing airborne noise and
minimising the transmission of noise through floors into other rooms.
The AgResearch Textile Team has experience in the acoustic properties of carpets and
clothing, having performed investigations for several textile companies, and has
collaborated with world-renowned acoustic experts.
Living in a noisy world
The impact and control of noise is becoming more important as we live and work more closely
together and roads get busier. Most of us want our homes to be quiet retreats from a noisy
world. Offices too, are becoming noisier as individuals' work spaces become smaller. Office
noise is known to reduce job satisfaction and productivity [1]. Noise is a particular problem for
those with impaired hearing who have difficulty picking out desired sounds from the confusion
of background noise. In restaurants without carpeted floors and/or soft wall coverings, normal
conversation can become difficult because of the large amount of sound generated on, and
reflected from, the hard floor.
The role of carpets
Why does nearly every car, cinema and passenger aircraft have carpet on the floors [2,3] and
sometimes on the walls as well? It is because carpeting is one of the most effective ways of
reducing noise. Carpets can absorb sound equally as well as some dedicated acoustic materials,
and reduce sound generation on, and propagation through, floors. Consequently, in the home
the acoustic properties of carpets provide comfort, while at the office they increase job
satisfaction and performance.
The acoustic benefits of wool carpet, together with their thermal and walking comfort, natural
ability to improve indoor air quality, inherent safety and sustainability [4-8], combine with their
aesthetics and prestige value to give the purchaser a justifiable feeling of satisfaction. The
superior acoustic properties of wool carpet are further enhanced by the use of an underlay.
Carpets are one of the few materials that can control noise in three ways.
1.
Airborne sound reduction
Sound is readily reflected from hard surfaces, which is why they make a room echoey. The
longer a sound bounces around a room the greater the overall sound level, making speech
indistinct and distant sounds seem closer. The porosity of the surface of carpets means
that sound waves can penetrate into the pile, rather than being reflected back into the
room as they would from a smooth surface (see the figure below). Absorption occurs as a
result of the sound waves causing vibrations in the individual fibres, pile tufts and
underlay. These components of carpets have different resonant frequencies at which they
© AgResearch Limited, 2014
best absorb sound, giving carpets the ability to absorb sounds over a wide range of
frequencies. This is particularly true with wool pile, as the natural variations in diameter,
crimp and length assist absorption across a wide frequency range.
Comparison of the airborne sound reductions of wool carpets and bare concrete [11].
2
Carpet, 10 mm, 1356 g/m . Underlay, 9.5 mm foam rubber.
2. Surface noise control
Surface noise is the sound from footsteps, dropped objects and furniture movement that
is heard in the room. Bare tile floors produce 7 to 12 times more surface noise than
carpets [9]. Carpets reduce this type of noise by cushioning objects on the floor and it is
this cushioning that also gives carpets their excellent walking and standing comfort
properties [2]. This type of noise control is particularly important in classrooms and busy
restaurants.
3.
Impact sound isolation
The reduction of transmission of footstep noise and the like through a floor to the room
below is clearly important for multi-storied buildings, lobbies, mezzanines, and balconies.
Carpets isolate sound by converting some of the high frequencies into less noticeable
lower ones. A footstep on concrete creates a high proportion of high frequency sound,
which will be heard as a sharp click or tap, whereas a carpet will change this to a muffled
thump. The thicker the carpet and underlay the greater the degree of sound isolation.
Carpets on underlay can isolate sound transmission so effectively that there is virtually no
competitive flooring alternative.
Effect of Wear
Trials under practical conditions showed a decrease in sound absorbing efficiency with heavy
wear of no more than 16%. After shampooing, which improves tuft definition, this loss was
reduced to 10% [10].
© AgResearch Limited, 2014
References
1.
Sundstrom E, Rice J P, Osborn O P and Brill M, Office noise, satisfaction, and performance. Environment
and Behaviour, 1994, 26(2), 195-222.
2.
Wang X, Subic A, Miller J and Lawry B, Vehicle floor carpet acoustic optimization. Proceedings of the 15
International Congress on Sound and Vibration 2008, 2736-2743.
3.
Woodcock R, Liu W, Sharma S, Dandaroy I and Bhuiyan M T, Modeling of carpet for aircraft interior noise
prediction. Proceedings of the Noise Control Conference, 2008, 372-379.
4.
Meade W, Consumer Properties of Carpets. WRONZ Technical Bulletin, January 1998. Wool Research
Organisation of New Zealand, Christchurch, New Zealand.
5.
McNeil S J, Sunderland M R and Zaitseva L I, Closed-loop wool carpet recycling. Resources, Conservation
and Recycling, 2007, 51(1), 220-224.
6.
Metcalfe P, The Frictional Advantages of Carpet in Slip Prevention. WRONZ Technical Bulletin, May 2003.
Wool Research Organisation of New Zealand, Christchurch, New Zealand.
7.
Ingham P, Fire Safety of Wool Carpets for Public Buildings. WRONZ Technical Bulletin, June 1999. Wool
Research Organisation of New Zealand, Christchurch, New Zealand.
8.
McCall R A and McNeil S J, Comparison of the energy, time and water usage required for maintaining
carpets and hard floors. Indoor and Built Environment, 2007, 16(5), 482-486.
9.
Study pinpoints acoustical properties of carpet. American Dyestuff Reporter, 1969, 58, 29-30.
10.
Meckel L, Sound absorbing properties of textile floor coverings. Melliand Textilberichte, 1982, 63, 335337.
11.
Data from Carpet Specifier's Handbook, The Carpet and Rug Institute, Dalton, USA, 1992.
th
For further information please contact Dr Steve McNeil
Tel: +64 3 3218650
Email: [email protected]
This publication has been prepared by AgResearch for stakeholders in the New Zealand wool industry, and is based on current knowledge. To the
extent of permissible by law, neither AgResearch nor any person involved in this publication accepts any liability for any loss or damage whatsoever
that may directly or indirectly result from any advice, opinion, representation, statement or omission, whether negligent or otherwise, contained in
this publication.
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Private Bag 4749, Christchurch 8140, New Zealand
T +64 3 3218800 F +64 3 3218811 www.agresearch.co.nz
© AgResearch Limited, 2014