250 Building acoustics
An example of the latter effect is given in Figure 6.24, which shows measurement
data and calculated results on single glazing. This example is used due to the complete
set of data given, both for the material and the geometry. Measurements are performed
using three separate sheets, each of area (560 x 1680) mm^2 , mounted together in a frame
making a total measuring area of (2020 x 1800) mm^2. Measurements were conducted on
samples of thickness 3, 4 and 6 mm, of which we are presenting the last two.
Figure 6.24 Sound reduction index of single glazing. Measured data reused by permission from Quirt (1982).The fit between measured and calculated results is very good for the 6 mm glazing,
whereas the expected lower reduction index for the 4 mm glazing does not show up in
the mass-controlled region. This discrepancy could be due to several factors; presumably
it is caused by the influence of the frame. It should be noted that the scale used for the
ordinate is different from the one used in Figure 6.23.
More recently, Callister et al. (1999) have reported on measurements and
calculations on single glazing using a test area much smaller than by Quirt, specifically
0.61m x 0.91 m. Their calculated results are based on Sewell’s expression for the
reduction index at low frequencies and Cremer’s Equation (6.101) for frequencies above
coincidence, together by a certain interpolation around the latter, following Sharp (1978).
Doing this, they obtain a very good agreement between measured and calculated results.
Finally, we shall use the example shown in Figure 6.24 to illustrate the relationship
between the resonant and non-resonant transmission in a specific case. Figure 6.25 again
shows measured data for 6 mm glazing plotted together with the predicted ones. In
63 125 250 500 1000 2000 4000Frequency (Hz)010203040Soundreduction index (dB)
Measured - 4 mm
Calculated - 4 mm
Measured - 6 mm
Calculated - 6 mm