Civil Engineering Reference
In-Depth Information
80
70
60
50
40
30
20
10
0
63
125 250 500 1000 2000 4000
Frequency (Hz)
Figure 8.27
Improvement in the impact sound insulation by a heavy floating floor, 50 mm concrete slab, 25 mm
mineral wool and 140 mm concrete basic floor. Measured data after Homb et al. (1983). Solid line - 9 dB per
octave above resonance frequency. Dashed line - predicted for an equivalent elastic unit mounting.
The solid straight line represents the predicted improvement following a frequency
dependence of 9 dB per octave above the resonance frequency, a curve that in this
example gives a slightly better estimate than what is actually achieved (see comments
below). It is also interesting to calculate the improvement in a thought experiment
assuming that the top floor floats on mounting units having the same total stiffness as the
mineral wool layer. The dashed line is calculated using Equation
(8.45)
, where an
empirical expression by Craik (1996) is used for the loss factor of concrete slabs (see
also section 6.4.2.3),
1
η=+
0.015.
(8.47)
f
It should be stressed that the latter result is included just to give an illustration of the use
of Equation
(8.45),
not because we expect that there should be a good fit to measured
data applied to a continuous elastic layer.
There exists, however, a series of measurement data on heavy floating floors on
continuous elastic layers that show a smaller frequency dependence than 9 dB per octave.
