Sound protection for windows refers exclusively to the protection against airborne sound. The key structural figure is the sound reduction index R, which describes the difference in volume between the sending and receiving room. The sound reduction index of a window is dependent on the type of glazing and the gap between the panes, the frame construction, the seals and the type of wall connection. However, roller shutter boxes and ventilation equipment must also be taken into account separately with their known sound reduction indexes as specified in their proof of suitability.
If sound protection improvements are planned as part of modifications or renovations, the aim should be to achieve an increase in the sound reduction index of 5 dB. Changes in the range from 0 dB to 2 dB are almost imperceptible to the human ear; 3 dB to 5 dB, however, is on the border of perceptibility. Significantly perceptible improvements are achieved with values from 6 dB to 10 dB.
The evaluated sound reduction index Rw is the simple identification of the assessment of the sound behaviour of glazing and windows. Rw encompasses only the sound transmission via the component without any diversions (e.g. connection joints) and is specified in dB. It is determined by taking measurements on a test bench at different frequencies. This method takes into account the fact that our ear responds less sensitively to sound sources with low frequencies (100 to approx. 400 Hertz) than to those with higher frequencies. These measurements are used to determine a type of average value. It thus becomes clear that sound-insulating glass products with the same evaluated sound reduction index can show significant differences at different frequencies.
By contrast, the apparent sound reduction index R’w takes into account the bypass transmission of the flanking component. It describes the actual sound insulation between two rooms and is compared with the requirement values in a sound protection measurement.
Considered in total
In practice, components are often made up of area ratios with different sound insulation, for example walls with doors or windows. The resulting sound reduction index Rw, res provides information about the sound protection properties of composite components and can be calculated if the sound reduction indexes of the individual component areas (Rw,i) are known.
Rw,res: resulting evaluated sound reduction index of the composite component (dB)
Rw,i: evaluated sound reduction index of the i-th component area (dB)
Si: i-th component area (m²)
Stot: total area of the composite component in the room (m²)
If the sound reduction index of the outside wall, the window area part and the required resulting structural sound reduction index R’res, w [dB] are known, the required evaluated sound reduction index of the windows can be calculated with the following formula:
SA: area of the windows or outside doors [m2]
St: total room outside component area [m2]
Rw,W,req: required evaluated sound reduction index of the windows [dB]
R‘w, OW: evaluated sound reduction index of the outside wall [dB]
R‘res, W: required evaluated resulting structural sound reduction index