Civil Engineering Reference
In-Depth Information
1.5
1.5
1
1
0.5
0.5
Prediction: TMM
Prediction: FTMM
Test (8ft
× 8
ft
×
4.5in)
Prediction: TMM
Prediction: FTMM
Test (8ft
× 8
ft
×
3in)
0
0
10
1
10
2
10
3
10
4
10
1
10
2
10
3
10
4
Frequency (Hz)
Frequency (Hz)
Figure 12.7
Reverberant absorption coefficient of 8
×
8 ft foam samples; tests versus
predictions.
1.5
1.5
1
1
0.5
0.5
Prediction: TMM
Prediction: TMM
Prediction: FTMM
Prediction: FTMM
Test1 (6ft
×
6ft
×
2in)
Test2 (6ft
×
6ft
×
2in)
Test (6ft
×
6ft
×
3in)
0
0
10
1
10
2
10
3
10
4
10
1
10
2
10
3
10
4
Frequency (Hz)
Frequency (Hz)
Figure 12.8
Reverberant absorption coefficient of 6
×
6 ft foam samples; tests versus
predictions.
Canada (NRC) Laboratory, in Ottawa. The laboratory volume is 250 m
3
.Thefoams
were mounted following Mounting A of ASTM C423. Two thicknesses were tested: 3
in (7.64 cm) and 4 in (11.34 cm). The material is modeled as limp. Figure 12.7 shows
the comparison between tests and the finite size correction (FTMM). The ideal random
incidence absorption (where finite size effect is omitted) is also shown. Overall good
agreement is observed for both thicknesses. The same foam was tested in a smaller
reverberation room at the Universite de Sherbrooke (143 m
3
in volume). The foam test
area was 6
×
6ft(1
.
829
×
1
.
829 m). Again, two thicknesses were tested: 2 in (5.04 cm)
and 3 in (7.62 cm). The results are shown in Figure 12.8. Again, it is seen that the FTMM
is able to capture the overall tendencies of the measured absorption curve.
12.4
Point load excitation
12.4.1 Formulation
This section discusses the use and application of the TMM for a structure-borne excita-
tion. Methods to calculate the response of a porous elastic material to a mechanical or
