Carpet softens harsh sounds and creates a quieter, more peaceful indoor environment.
The installation of carpet and underlay is the only method available for eliminating excessive noise generated by floor impacts such as noise produced from footfalls, chairs scraped across the floor and objects dropped on the floor. This is particularly important in homes where children running and jumping can produce heavy floor impacts, contributing greatly to ambient noise levels.
Carpet and underlay also help to control sound reverberation, the term used to describe the degree to which sound lives on within a room. Reverberant homes are generally noisy and ‘echoey’ places where speech communication, particularly over the phone, is difficult.
The installation of carpet and underlay will bring long reverberation times down to acceptable levels. While there are other sound absorption alternatives such as acoustic ceiling tiles and panels, they do not reduce floor impacts and for this reason cannot achieve the same overall reduction in noise levels.
Noise attenuation is yet another reason why carpet is an excellent floor covering choice where functionality and fashion are important.
Excessive indoor noise is a major problem in the community. Unwanted noise can:
- cause stress and affect human wellbeing
- impair productivity in the workplace and the classroom, and
- affect patient outcomes in hospitals and aged care facilities.
A range of factors contribute to the increased level of concern about acoustic privacy and these include:
- open plan offices and homes
- a large increase in the number of people living in town houses and apartments
- inadequacy of existing impact sound insulation regulations.
Carpet can significantly improve the functionality of indoor spaces by reducing unwanted noise.
Floor Impact Noise
Carpet virtually eliminates floor impact sounds such as noise produced by footfalls, chairs scraped across the floor, and objects dropped onto the floor.
According to acoustical consultants, Graeme E Harding and Associates (GEHA):
“The installation of carpet or similar types of floor covering is the only method available for eliminating excessive noise generated by floor impacts. Carpeted floors can result in a reduction in noise of over 20 decibels.” This is particularly important in schools, busy offices, health care facilities and in the home with children, where floor impact sounds can contribute greatly to ambient noise levels.
The pile structure of carpet also helps to control reverberation. A material’s potential for reverberation control is quantified by its Noise Reduction Coefficient (NRC) and/or by its Weighted Sound Reduction Coefficient, αw (pronounced ‘alpha w’). A typical broadloom carpet has an NRC of 0.35 and will absorb approximately 35% of sound that strikes it. The NRC rating of carpet is directly proportional to the thickness of the floor covering. If the carpet is installed with an underlay its NRC rating will almost double. NRC ratings of common room finishes are provided in Table 1.
Table 1 : Noise Reduction Coefficients (NRC)
|Material||Noise Reduction Coefficient (approximate)|
|Carpet with underlay||0.65|
|Acoustic ceiling tile||0.55 to 0.95|
AS/NZS 2107:2000: Recommended Design Sound Levels and Reverberation Times for Building Interiors provides recommended reverberation times (T60) for a range of indoor environments in order to ensure good speech intelligibility, control of noise and a degree of acoustic privacy.
Recommendations for common spaces are shown in Table 2.
Table 2 : Recommended Reverberation Times
|Type of occupancy||Recommended reverberation time (T60)|
|General office areas||0.4 to 0.6 seconds|
|Private offices||0.6 to 0.8 seconds|
|Primary school classrooms||0.4 to 0.5 seconds|
|Domestic living areas||Less than 0.8 seconds*|
* GEHA recommendation (AS/NZS 2107 does not include advice for T60 in domestic spaces).
Reverberation times for common spaces with and without carpet were calculated by GEHA using CSIRO test data commissioned by the Carpet Institute. In all cases, installation of carpet and underlay was predicted to bring excessively long reverberation times down to acceptable levels.
Noise attenuation is another reason why carpet is the best floor covering choice where functionality and fashion are important.
Impact Sound through Floor / Ceiling Systems
Noise from footfall in the apartment above is a common source of complaint among modern apartment dwellers.
Building Code of Australia (BCA) Acoustic Criteria
The BCA incorporates Deemed-to–Satisfy provisions for impact sound insulation of floor / ceilings separating apartments.
The Carpet Institute commissioned CSIRO acoustical laboratories to test a range of carpets for impact sound insulation in accordance with the BCA requirements. All floors tested with carpet were found to easily pass the BCA criterion for impact sound. Results are summarized in Table 3.
Table 3 : Impact Sound Insulation Values and BCA Requirements
|Product||Impact sound rating (Ln,w + CI, dB)||Performance|
|Requirements for Class 2 & 3 buildings||62 or less|
|Carpet with underlay on concrete||30||Excellent impact sound insulation|
|Carpets without underlay on concrete||42||Good impact sound insulation|
|Concrete floor||68||Inadequate impact sound insulation|
Carpet is the most effective and practical option for protecting residents of multi-storey buildings from impact generated noise from occupancies above.