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Open windows with good sound insulation

We have translated the report published by the Danish Environmental Protection Agency (you can download the original report in Danish here).  We are sharing this information to increase its international impact.  Although the research is in the context of Danish regulations and requirements, the ideas and test data are useful in many different scenarios.

Download the English translation here.

Summary and conclusions

Three different window types are examined to increase the sound insulation:
A.  Further development of the “Air supply window”, a plenum window arrangement.
B.  A conventional window with an internal solution.
C.  A conventional window with an external solution.

An ordinary window in an open position has a low sound insulation that for some situations are not sufficient to meet the Danish requirements for indoor noise level. The primary project objective was to research alternatives to an ordinary open window that both has wide-ranging sound insulation, but also have diverse dimensions, absorption material locations and structural additions such as an external solution.  Many laboratory measurements with different types of windows were conducted. The laboratory measurements were supplemented by field measurements. The report presents the measurements and the subsequent conclusions.

An optimised version of the “Air supply window” (sometimes called a “plenum window”) was developed with a focus on sound insulation for low frequencies. In contrast to previously developed solutions, perforated casings were tuned to dampen the low frequency part of the spectrum.

An internal solution to increase the sound insulation of a standard window was developed.  Improvements are seen in several steps: first by adding an additional window (i.e. overall double construction), next, by adding a sliding window into the cavity, and finally by adding absorption in the cavity of the window.

An external solution to increase the sound insulation of a standard window was developed. It does not require any changes to be made on the window opening or the window itself. The solution is based on an external design in the form of an attached sound-lock which is connected to a window frame that opens out into the sound-lock. This may be particularly suitable for refurbishment purposes.

Comparative field and laboratory measurements were conducted on an air supply window to investigate differences between field and laboratory measurements. There is a higher sound insulation for field measurements than laboratory measurements, especially for frequencies below 250 Hz. The difference in Rw+Ctr is 2-4 dB. An explanation could be the difference in sound incidence. Hence it could be possible that the difference could be greater for window types in which the opening does not
face the noise source.

The three window types investigated range widely in sound insulation, dimensions and design / solution principles. For the three window types, the laboratory sound insulation as Rw+Ctr was measured respectively as 26, 12 and 17 dB with an opening area of 0.35 m2. Laboratory sound insulation as Rw+Ctr for an ordinary open window are in the range of 5-8 dB with an opening area of 0.35 m2.  Therefore the improved sound insulation performance is in the range of 4 – 21 dB for the different solutions.

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