Last update: 15.10.2020
Sound control

Sound ratings for buildings

A building component (e.g. glass) with a noise reduction capacity rating of 40 dB will reduce 70 dB of outside noise to 30 dB on the inside of the building - a noticeable reduction that is approximately 5 % of the outdoor noise level.

When working with buildings, it is not possible to consider the individual building in terms of noise level. The entire periphery around the building must be taken into account in order to calculate the total dB possible for sound reduction.

Average noise reduction factor (Rw)

The noise for solid objects is defined according to EN 20140, EN ISO 717 and EN ISO 140 and indicated as Rw in dB. This is carried out by measuring and comparing a reference curve. Rw represents an average sound insulation over the relevant frequencies.

Average noise reduction factor (Rw)

Here, the reference curve is moved vertically, providing that the lower deviation does not exceed 2 dB. An overshooting is not taken into account. The value of the ordinates of the moved reference curve at 5,000 Hz then complies with the average evaluated noise reduction value of Rw. In addition, particularly in Germany, DIN 4109 must be considered. This defines the following nomenclature:

R    = evaluated noise reduction extent in dB with no noise transfer over the adjacent components (just the net glass value, for example).
Rw    = weighted sound reduction index in dB with sound transmission via adjacent structural components (for example windows).

Rw, res    = resulting sound reduction index in dB of the entire structural component (e.g. entire wall inc. windows consisting of frames with glass and structural connections).

Rw,P    = weighted sound reduction index in dB, determined on a test station.

Rw,R    = weighted sound reduction index in dB, calculation value.

Rw,B    = weighted sound reduction index in dB, values measured on the construction.

Correction factors (C, Ctr)

This correlation can be used to compare and calculate individual acoustic components in order to arrive at the total sound level. However, real-life applications have shown that, depending on the noise source for these Rw mean values, there are certain correction factors that should be taken into account, which are also defined in the standard EN 717-1.

Spectrum adaptation value

* In several EU countries, there are computational methods for the fixation of octave band sound levels for road and rail traffic noise. These can be used for comparison with the spectra of 1 and 2.

These correction factors, i.e. spectrum adaptation values C and Ctr, reduce the sound reduction index Rw of the component if the noise sources conforming to the EN list are causative. 

This means for a typical glazing of Rw (C, Ctr) = 42 (-1 ; -5)        
Rw            = 42 dB
Rw+C    = 42 – 1     = 41 dB
Rw+Ctr    = 42 – 5     = 37 dB

The corrections are based on the A-weighted sound spectra (→ chapter 6.2.2).

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