The Measurement of Double Decay Rates in Small Enclosures Containing Highly Absorbent Samples

Abstract

One common method of obtaining the absorption properties of a sample of material is to measure the decay of sound in an enclosure partially lined with the sample. In order to infer absorption coefficients from decay rate measurements, it is assumed that the sound field in the enclosure is diffuse. When measurements are made in enclosures which are small compared with wavelength, and contain non-uniform absorption, the diffuse field may no longer be three-dimensional in nature. Descriptions are given of measurements made in a small rectangular enclosure with one surface lined with highly absorbent material, and the results presented. Predictions are made of the decay rates in this situation and compared with the experimental results. Finally, the different field states present during the decay are explored.

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References

Sabine

W.C.

, Collected Papers on Acoustics Dover Publications, (1964).

ISO 354 - 1985 (E) ‘Measurement of Absorption Coefficients in a Reverberation Room’.

Balachandran

C.G.

, and Robinson

D.W.

, ‘Diffusion of the Decaying Sound Field’, Acustica 19 (1968) pp. 245–257.

Mechel

F.P.

, Schallabsorber Vol. 1, S. Hirzel Verlag, (1989). Chap. 4.

Yegnanarayana

, and Balachandran

C.G.

, ‘Studies in a Reverberation Room with a Highly Absorbing Sample’, J. Acoust. Soc. Amer. 52 (1972), pp. 465–470.

Hirata

, ‘Geometrical Acoustics for Rectangular Rooms’, Acustica 43 (1979), pp. 247–252.

Tokyama

and Suzuki

, ‘Reverberation Time in Almost Two Dimensional Diffuse Field’, J. Sound Vib. 111 (1986), pp. 391–398.

Nilsson

, ‘Decay Processes in Rooms with Non-Diffuse Sound Fields’, Lund Institute of Technology Sweden, Report TVBA-1004 (1992).

Young

R.W.

, ‘Sabine Reverberation Equation and Sound Power Calculations’, J. Acoust. Soc. Amer. 31 (1959), pp. 912–921.

10.

Fitzroy

, ‘Reverberation Formula Which Seems to Be More Accurate with Nonuniform Distribution of Absorption’, J. Acoust. Soc. Amer. 31 (1959), pp. 893–897.

11.

Knudsen

V.O.

Delsasso

L.P.

, and Leonard

R.W.

, ‘Reverberation - Room Acoustics - Effects of Various Boundary Conditions’, J. Acoust. Soc. Amer. 42 (1967), p. 953–965.

12.

Yegnanarayana

, ‘Wave Analysis of Sound Decay in Rectangular Rooms’, J. Acoust. Soc. Amer. 56 (1974), p. 534–541.

13.

Kuttruff

, ‘On the Acoustics of Auditoria’, Building Acoustics 1 (1994), pp. 27–48.

14.

Schroeder

M.R.

and Kuttruff

K.H.

, ‘On Frequency Response Curves in Rooms: Comparison of Experimental Theoretical and Monte Carlo Results for the average Frequency Spacing between Maxima’, J. Acoust. Soc. Amer. 34 (1962), pp. 76–80.

15.

Crighton

D.G.

Dowling

A.P.

Ffowcs

J.E.

Williams

Heckl

F.G. Leppington

, Modern Methods in Analytical Acoustics London: Springer Verlag (1992).

16.

Olynyk

and Northwood

T.D.

, ‘Comparison of Reverberation - Room and Impedance - Tube Absorption Measurements’, J. Acoust. Soc. Amer. 36 (1964), pp. 2171–2174.