Broadband noise absorption, including low frequencies, may be obtained by a hybrid passive–active two-layer system. A porous layer in front of an air layer provides passive absorption, at medium and high frequencies. Active control of the input impedance of the two-layer system yields absorption at low frequencies. The active control system can implement either pressure-release or impedance-matching conditions. A simple analytical model based upon plane waves propagating in a tube permits the comparison of both control strategies. The results of this simple model show that the pressure-release condition affords higher absorption than the impedance-matching condition for some combinations of geometrical and material parameters. Experimental results corroborate the good performance of the pressure-release condition under the prescribed geometrical setup.

1.
Allard
,
J. F.
, and
Champoux
,
Y.
(
1992
). “
New empirical equations for sound propagation in rigid frame fibrous materials
,”
J. Acoust. Soc. Am.
91
,
3346
3353
.
2.
Beyene
,
S.
, and
Burdisso
,
R. A.
(
1997
). “
A new hybrid passive/active noise absorption system
,”
J. Acoust. Soc. Am.
101
,
1512
1515
.
3.
Delany
,
M. E.
, and
Bazley
,
E. N.
(
1970
). “
Acoustical properties of fibrous absorbent materials
,”
Appl. Acoust.
3
,
105
116
.
4.
Elliott, S. J. (2001). Signal Processing for Active Control (Academic, London), pp. 132–166.
5.
Furstoss
,
M.
,
Thenail
,
D.
, and
Galland
,
M. A.
(
1997
). “
Surface impedance control for sound absorption: Direct and hybrid passive/active strategies
,”
J. Sound Vib.
203
,
219
236
.
6.
Guicking
,
D.
,
Karcher
,
K.
, and
Rollwage
,
M.
(
1985
). “
Coherent active methods for application in room acoustics
,”
J. Acoust. Soc. Am.
78
,
1426
1434
.
7.
Guicking
,
D.
(
1990
). “
On the invention of active noise control by Paul Lueg
,”
J. Acoust. Soc. Am.
87
,
2251
2254
.
8.
Hansen, C. H., and Snyder, S. D. (1997). Active Control of Noise and Vibration (Spon, London), pp. 559–576.
9.
Mechel
,
F. P.
(
1988
). “
Design charts for sound absorber layers
,”
J. Acoust. Soc. Am.
83
,
1002
1013
.
10.
Nelson, P. A., and Elliott, S. J. (1992). Active Control of Sound (Academic, London), pp. 161–179.
11.
Orduña-Bustamante
,
F.
, and
Nelson
,
P. A.
(
1992
). “
An adaptive controller for the active absorption of sound
,”
J. Acoust. Soc. Am.
91
,
2740
2747
.
12.
Smith
,
J. P.
,
Johnson
,
B. D.
, and
Burdisso
,
R. A.
(
1999
). “
A broadband passive–active sound absorption system
,”
J. Acoust. Soc. Am.
106
,
2646
2652
.
This content is only available via PDF.
You do not currently have access to this content.