Ensemble averaged surface normal impedance of material using an in-situ technique: preliminary study using boundary element method.

An in-situ measurement technique of a material surface normal impedance is proposed. It includes a concept of "ensemble averaged" surface normal impedance that extends the usage of obtained values to various applications such as architectural acoustics and computational simulations, especially those based on the wave theory. The measurement technique itself is a refinement of a method using a two-microphone technique and environmental anonymous noise, or diffused ambient noise, as proposed by Takahashi et al. [Appl. Acoust. 66, 845-865 (2005)]. Measured impedance can be regarded as time-space averaged normal impedance at the material surface. As a preliminary study using numerical simulations based on the boundary element method, normal incidence and random incidence measurements are compared numerically: results clarify that ensemble averaging is an effective mode of measuring sound absorption characteristics of materials with practical sizes in the lower frequency range of 100-1000 Hz, as confirmed by practical measurements.

[1]  Miko Elwenspoek,et al.  The μ-flown: A novel device for measuring acoustic flows , 1996 .

[2]  Toru Otsuru,et al.  In situ measurements of surface impedance and absorption coefficients of porous materials using two microphones and ambient noise , 2005 .

[3]  E. Mommertz,et al.  Angle-dependent in-situ measurements of reflection coefficients using a subtraction technique , 1995 .

[4]  K. Attenborough.  Acoustical characteristics of rigid fibrous absorbents and granular materials , 1983 .

[5]  Yasuhito Kawai,et al.  Estimation of the area effect of sound absorbent surfaces by using a boundary integral equation , 2002 .

[6]  Claude Depollier,et al.  Free field surface impedance measurements of sound-absorbing materials with surface coatings , 1989 .

[7]  A. L'Esperance,et al.  Anisotropy effect in glass wool on normal impedance in oblique incidence , 1987 .

[8]  Jean Nicolas,et al.  Measurement of acoustic impedance in a free field at low frequencies , 1988 .

[9]  C. Nocke.  In-situ acoustic impedance measurement using a free-field transfer function method , 2000 .

[10]  Y. Miki.  Acoustical Properties of porous materials : Modifications of Delany-Bazley models , 1990 .

[11]  Jonathan D Blotter,et al.  Measurement of sound power and absorption in reverberation chambers using energy density. , 2007, The Journal of the Acoustical Society of America.

[12]  Massimo Garai,et al.  Measurement of the sound-absorption coefficient in situ: The reflection method using periodic pseudo-random sequences of maximum length , 1993 .

[13]  Finn Jacobsen,et al.  A comparison of two different sound intensity measurement principles , 2005 .

[14]  Kenichi Ishikawa,et al.  Measurements of acoustic impedance and their data application to calculation and audible simulation of sound propagation , 2008 .

[15]  T.G.H. Basten,et al.  Two complementary Microflown based methods to determine the reflection coefficient in situ , 2006 .

[16]  E. N. Bazley,et al.  Acoustical properties of fibrous absorbent materials , 1970 .

[17]  D. A. Blaser,et al.  Transfer function method of measuring in-duct acoustic properties. I - Theory. II - Experiment , 1980 .

[18]  A. F. Seybert,et al.  Experimental determination of acoustic properties using a two‐microphone random‐excitation technique , 1977 .

[19]  Finn Jacobsen,et al.  A note on the calibration of pressure-velocity sound intensity probes , 2006 .

[20]  Yvan Champoux,et al.  Pressure variation above a layer of absorbing material and impedance measurement at oblique incidence and low frequencies , 1989 .

[21]  J. F. Allard,et al.  In situ two-microphone technique for the measurement of the acoustic surface impedance of materials , 1989 .