Civil Engineering Reference
In-Depth Information
3.9
Example
The impedance
Z
of a layer of anisotropic fibrous material is represented in Figure 3.12.
The normal flow resistivity
σ
N
and the thickness
d
of the material are respectively
σ
N
=
25 000 N m
−
4
sand
d
2
.
5cm.
The impedance at 630 Hz is represented as a function of the angle of incidence
θ
for three values of the anisotropy factor
s
=
σ
P
/σ
N
=
1, 0.6, 0.3. A value of
s
close to
0
·
6 was obtained in measurements performed on several glass wools (Nicolas and Berry
1984, Allard
et al
. 1987, Tarnow 2005).
=
References
Allard, J.F., Bourdier, R. & L'Esperance, A. (1987) Anisotropy effect in glass wool on normal
impedance in oblique incidence.
J. Sound Vib
.,
114
, 233 -8.
Cremer, L. and Muller, A. (1982)
Principles and Applications of Room Acoustics
. Elsevier Applied
Science Publishers, London.
Delany, M.E. and Bazley, E.N. (1970) Acoustical properties of fibrous materials.
Applied Acoustics
,
3
, 105 - 16.
Nicolas, J. and Berry, J.L. (1984) Propagation du son et effet de sol.
Revue d'Acoustique
,
71
,
191 - 200.
Tarnow, V. (2005) Dynamic measurement of the elastic constants of glass wool.
J. Acoust. Soc.
Amer
.
118
, 3672 - 3678.
