Appendix 1 - Acoustic Fact Sheet

FACT SHEET
             Example: If one is interested in the TL     Thermal Advantages of Concrete’
             value of a glass panel (density ~ 2700kg/   by Paul Uno) shows the reduction in
             m3) with thickness 6 mm at a frequency      sound level efficiency when openings
             of 500 Hz (ie this frequency corresponds    of different sizes are present in panels.
             to the C above middle C on a piano)         For example, if a panel has a sound
             then the m value would be 0.006 x 2700      transmission rating of 50 dB (when
             = 16.2 kg/m2, the mf value would be         appropriately sealed) and an opening
             16.2 x 500 = 8100 kg/m2.Hz and thus the     in that panel which only constitutes 0.01
             TL would be 30 dB.                          % of the area of that panel (eg a 20mm
                                                         diameter hole in a 2.4m x 1.2m panel),
             Weak Links                                  then the panel will now only have a 40
             Whilst the information above gives the      dB rating – well below most accepted
             designer a good reference point to start    ratings for building design.
             with when trying to account for noise
             levels in buildings, much of this noise     Figure 1
             reduction can be forfeited if the so-
             called ‘weak links’ are not understood      Insualtion vs % Openings
             and accounted for when designing a
             structure.

             (a) Flanking
             Noise entering a structure does not
             always follow a direct path from an
             outside noise source through the wall in
             question, to the person inside hearing
             the noise. Often the sound waves
             can enter from indirect paths such as
             through ceilings, service penetrations
             and joints. This being the case, a
             designer needs to reduce the noise
             levels from these flanking paths (eg
             providing separation materials between
             walls and/or ceilings; caulking perimeter
             walls –again refer to the Handbook for
             more detail).                               (c) Windows
                                                         Glazing is obviously a key part of any
             (b) Openings, Holes & Cracks                building envelope and as such the
             Any concrete element will have its          designer has to take into account the
             acoustic rating downgraded if openings,     limitations of glass with respect to
             holes or cracks are left in the element     acoustic efficiency. The transmission loss
             after installation and during the life of   of standard residential glass is around 25
             the element. These openings provide an      dB and for 6mm commercial thickness
             avenue for sound waves to penetrate
             directly through the panel. Figure I
             below (reproduced from an ABIC 1992
             conference paper titled ‘Acoustic &
                                                                         making precast easy