Effect Of Area
The larger the window area, the more acoustic energy is able to pass through it. However, because of the way in which sounds add together, this is not a dominant effect. If the opaque parts of a façade (walls) are considered to have a sound insulation at least 10 dB higher than the window, then each halving of window area increases the effective sound insulation by 3 dB. If, for example, a 100% (fully) glazed façade had a sound insulation of 30 dB, changing to 50% and 25% glazed façades would secure corresponding aggregate sound insulations of 33 dB and 36 dB, respectively.

Effect Of Distance
With increasing distance from a noise source, there is a corresponding decrease in noise level. The decay rate is dependent upon whether the source originates at a point or over an area, which, in turn, depends on its shape and the distance at which the sound is heard.

Noise from an aircraft or a single vehicle may be considered to be a point source, and the decay rate approximates to 6 dB per doubling of distance. Noise from a line of traffic or railway train does not diminish as rapidly; 3 dB per doubling of distance is a typical decay rate.

For example, if a roadside noise measurement, 5 metres from the vehicles, indicates a level of 78 dBA, this would reduce correspondingly to 75 dBA at 10 metres, to 72 dBA at 20 metres and to 69 dBA at 40 metres. This 9 dBA drop in level from the initial measurement is almost equivalent to a halving in its perceived loudness at the kerbside.

Effect Of Height
With increasing building height, there should be an associated decrease in received street noise level, but the acoustic horizon of the upper floors is correspondingly increased. These are opposing trends, and the result is that the vertical noise field is almost uniform.

Barriers
Sound waves have long wavelengths, as mentioned earlier. Therefore diffraction effects are significant; that is, bending around obstacles is relatively easy. Fences, earth mounds and screens are therefore relatively ineffective, unless positioned either close to the source or close to the reception point. Window furniture, like blinds, has no influence on the noise transmission through windows.

Other Glazing Types
Apart from lamination, other glass types do not exhibit any departures from the sound insulation of ordinary clear float glass. Thickness for thickness, toughened, wired, coated and tinted glass products have exactly the same acoustic performance. Patterned glass products, which have surface indentations, behave identically to ordinary clear float glass of the same average thickness.

Fixing Effects
Better sound insulation is achieved by installing glass in resilient gaskets instead of tightly clamping it with beads. Any structural vibrations are then less able to be transmitted to the glass, thus maintaining its acoustic integrity.