Appendix 1 - Acoustic Fact Sheet

FACT SHEET
             glass it is around 30 dB. If one puts         Chart A - Composite Walls Sound
             glazing into a precast concrete panel         Insulation
             where the panel thickness is 150mm (TL
             = 50 dB) and the glazing is a single 6mm
             sheet (TL = 30 dB) then one cannot
             simply just average the two acoustic
             ratings as both values are logarithmic
             units. Whilst the mathematics is
             complicated for non-mathematicians,
             Chart A quantifies this ‘composite
             grading’ process.

             From Chart A it can be seen that if
             the concrete panel is 6.0m x 2.4m and
             the glazing is 1.2 x .2m, then the ratio
             of the small panel to the large panel
             is (1.2 x 1.2 / 6.0 x 2.4 = 0.10 or 1: 10).
             The acoustic rating difference between
             panels is 20 dB so the ‘loss of insulation’
             from the higher value is 9 dB which
             means the composite panel TL value is
             41 dB.

             If however, the panel contained a louvre      Summary
             panel for air-intake (which has no sound      In conclusion, when one is concerned
             insulation) rather than the glass panel,      about acoustic performance in building
             then the sound level difference between       construction, precast concrete is seldom
             the two panels would be 50 – 0 = 50           a concern as it has excellent sound
             dB, and thus the composite partition          transmission loss properties.
             TL value would be 10 dB (i.e. 50 dB
             minus 40 dB where the latter value            As well as performing well acoustically,
             corresponds to the x axis value from          aspects such as quality control, curing
             the chart for 50 dB difference and 1:10       and crack elimination are issues which
             ratio).                                       have been addressed during the
                                                           manufacturing process.

                                                           This is sometimes not the case
                                                           with concrete which is not factory-
                                                           manufactured. For example, lack of
                                                           vibration on site may result in incorrect
                                                           element density, thus the mass of the
                                                           panel is reduced leading to small TL (Rw)




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