Acoustics

Congestion and noise pollution are increasing through the country as development spreads further into the countryside and densities become higher in urban area.  It is becoming more commonplacefor building designers and homeowners to want to know the acoustic ratings for standard windows and some projects have the acoustical specifications written on them now. 

Depending on the acoustic values and qualities you are looking for in a window, there are various factors to consider:

• There is no significant difference between laminated and monolithic glass. The total glass thickness excludes the laminate thickness.
• There is no systematic dependence on frame material. It is easier to obtain the necessary good sealing and reduce flanking transmission through the frame with solid, filled or heavier frame cross sections.
• There is no systematic dependence on the type of opening. It is easier to obtain the necessary good sealing as the design is changed from sliding through double hung, casement and awning to fixed.
• Good sealing is important. These sound insulation values apply to windows and glass doors whose air infiltration at + 75 Pa is less than 5 l/s/m2 when tested in accordance with the Australian Standard AS 4420.4-1996 "Windows - Methods of Test - Air infiltration". Higher air infiltration will give lower sound insulation. The detrimental effect of air infiltration increases as the sound insulation increases.
• The sound insulation values apply to windows and glass doors with areas between 1 and 5 m2. Larger areas will give lower sound insulation.
• Monolithic or laminated glass of the same total glass thickness as the narrow gap type will have slightly greater sound insulation than the narrow gap type, and could be used instead of the narrow gap type if the increased thermal insulation of the narrow gap type is not needed.
• The sound insulation values are the A-weighted sound pressure level attenuation of urban road traffic noise when passing through the window or glass door. More specifically, the sound insulation values are the sum of the weighted sound reduction index (Rw) and the traffic noise spectrum adaptation term (Ctr) defined in Australian and New Zealand Standards AS/NZS 1276.1-1999 "Acoustics - Rating of sound insulation in buildings and of building elements Part 1: Airborne sound insulation".
• The sound insulation values can be used as Aircraft Noise Attenuation of facade component (ANAc) values in Australian Standard AS 2021-1994 "Acoustics - Aircraft noise intrusion - Building siting and construction".
• The sound insulation values can be used as Traffic Noise Attenuation of facade component (TNAc) values in Australian Standard AS 3671 - 1989 "Acoustics - Aircraft noise intrusion - Building siting and construction".
• The sound insulation values also apply to railway noise. An Australian Standard on railway noise intrusion into buildings is in preparation.
• The windows and glass doors must be installed and sealed into the building facade in a manner that introduces no significant extra air infiltration.
• Each 10 dB increase in the sound insulation corresponds to a perceived halving of the loudness of the transmitted sound. The smallest change in sound insulation that is perceptible to the human ear is 3 dB.
• Sixty-six sound insulation measurements were analysed to obtain these generic sound insulation ratings. Fifty of them were grouped into the five generic types shown in the table of measurement results (from 'The sound insulation of domestic Australian windows and glass doors', John Davy, CSIRO,2000) with at least five measurements in each group. Apart from the 6mm - 4mm and the 4mm - 3mm differences, the sound insulation values are statistically significantly different.
• All of the sound insulation measurements above 32 dB used special seals. None of the sound insulation measurements below 25 dB used special seals.
• Most of the window sand glass doors had equal areas of fixed and opening glazing.
• Thirteen of the windows and glass doors also had their air infiltration measured at + 75 Pa. There was a slight but non-monotonic decrease in the sound insulation values as the air infiltrations values increased. Due to the small number of measurements the decrease was not statistically significant.
• All the sound insulation measurements analysed are on real windows and not on just the glazing.
• Windows designed for good sound insulation should also be certified for structural performance and water infiltration. There have been cases of acoustical windows leaking badly.
• The Sound Transmission Class (STC) and the weighted sound reduction index (Rw), which are used for rating the sound insulation of internal walls, are NOT appropriate for rating the sound insulation of facade component such as windows and glass doors. The reason is that the traffic noise spectrum adaptation term has an average value of -5 dB and varies between - 13 and 0 dB. this is due to the fact that typical external noise has much more low frequency energy and typical internal noise.