The complementary strengths and weaknesses of passive and active noise control (ANC) methods have motivated many researchers to develop hybrid noise absorbers that integrate both control strategies. The impedance matching technique (IMT) is the most effective for such a purpose. An unsolved problem with available IMT schemes is the a priori reference signal that limits IMT applications. This study proposes the use of the forward wave, available by the two-microphone method, as the reference signal. Due to inevitable errors in wave separation and inlet reflection of the control signal, the absorber becomes a feedback system. A simple and stable ANC is developed for impedance matching without the a priori reference signal. The proposed absorber has an absorption coefficient of 0.9 or above in a frequency range of 60–850 Hz. It is stable in the presence of sensor mismatch and robust with respect to significant variation of inlet boundary conditions.

1.
U. Ingard, Notes on Sound Absorption Technology (Noise Control Foundation, Poughkeepsie, NY, 1994).
2.
D.
Guicking
and
E.
Lorenz
, “
An active sound absorber with porous plate
,”
J. Vibr. Acoust.
106
,
389
392
(
1984
).
3.
D.
Thenail
,
M.
Galland
,
M.
Sunyach
, and
M.
Sunhack
, “
Active enhancement of the absorbent properties of a porous material
,”
Smart Mater. Struct.
3
,
18
25
(
1994
).
4.
C. R. Fuller, M. J. Bronzel, C. H. Gentry, and D. E. Whittington, “Control of sound radiation/reflection with adaptive foams,” Proceedings of Noise-Con 1994, Fort Lauderdale, FL, pp. 429–436.
5.
S.
Beyene
and
R.
Burdisso
, “
A new hybrid passive/active noise absorption system
,”
J. Acoust. Soc. Am.
101
,
1512
1515
(
1997
).
6.
J. P.
Smith
,
B. D.
Johnson
, and
R. A.
Burdisso
, “
A broadband passive-active sound absorption system
,”
J. Acoust. Soc. Am.
106
,
2646
2652
(
1999
).
7.
F. J. Fahy, Sound Intensity, 2nd ed. (E & FN Spon, London, 1995).
8.
J. W.
Parkins
,
S. D.
Sommerfeldt
, and
J.
Tichy
, “
Error analysis of a practical energy density sensor
,”
J. Acoust. Soc. Am.
108
,
211
222
(
2000
).
9.
“Standard test method for impedance and absorption of acoustical materials by the impedance tube method,” ASTM C384, Philadelphia, 1990.
This content is only available via PDF.
You do not currently have access to this content.