The standard "EN ISO 11654 Acoustics - Sound absorbers for use in buildings - Degree of sound absorption", which is based on a European standard and was developed by the International Organization for Standardization (ISO), describes a method by which the frequency-dependent values of the sound absorption coefficient can be converted into a single number. Before this is done, the one-third octave band values of the sound absorption coefficient measured in accordance with the standard "ISO 354 Acoustics - Measurement of sound absorption in a reverberation room" are converted into octave bands. In the annex of the standard, a classification method based on these single numbers is given for information purposes (Annex B).
The single number rating specified in this standard can be used to formulate the requirements and describe the acoustic properties of sound absorbing products to be used in normal offices, corridors, classrooms, hospitals and similar routine applications. The rating is not appropriate if the products are used in specialized environments requiring careful acoustic design. In such cases, only the full sound absorption data as a function of frequency is satisfactory.
This standard is not applicable unless the reference curve covers the full frequency range. If only part of this range is of interest, it may be more appropriate to look for products with good sound absorption only in this range. The shape indicators described in this standard provide some guidance in identifying such products, which may have a relatively low single number but may have a much higher potential when a more restricted frequency range is considered. Such products are evaluated from the full sound absorption curve.
Since the rating curve in this standard has the 250 Hz octave band as the lower limit, rating is not suitable below this frequency. If such low frequencies are of interest, the full sound absorption curve should be consulted.
This standard is, in principle, applicable to all building products for which the sound absorption coefficient is determined in accordance with ISO 354. However, it is generally not suitable for application to single items such as chairs, deflectors and the like, and is not applicable to road barriers and road surfaces.
For the purposes of this standard, the following definitions apply:
API values are used to calculate the weighted sound absorption coefficient from the reference curve shown in the figure given in the standard. The reference curve is shifted in steps of 0,10 toward the measured value until the sum of the negative deviations is less than or equal to 0,05. A negative deviation occurs at a given frequency when the measured value is less than the value of the reference curve. Only negative deviations are counted. The weighted sound absorption is defined as the value of the shifted reference curve at 500 Hz. Examples of calculations of the weighted sound absorption coefficient are included in the appendix of the standard (Annex A).
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