The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.

ARTICLE REFERENCE

Article: A critical study of the precision of measurement of absorption coefficients by reverberation methods

Author: Paul E. Sabine

Publication Date: July 1931 (JASA 3, 139); https://doi.org/10.1121/1.1915551

Paul E. Sabine was a distant cousin of Wallace C. Sabine. He continued Wallace's work at Riverbank Laboratories in Illinois after his cousin's death in 1919. His main focus was the development of Riverbank Labs into one of the leading testing institutions in the United States, even before “sound chambers” were built at the National Bureau of Standards (today NIST) and at universities. Paul's work focused on absorption coefficient measurements, and he published a series of articles on that topic.1–6 He was strongly concerned with the precision of measurement of absorption coefficients by reverberation methods1 and demonstrated the error of the measured value of the absorption coefficient when the reverberation time is not determined precisely. He was aware of the large variability of the measured absorption coefficient of the same sample in different laboratories. He investigated various source types (organ pipe and loudspeaker), and measured the reverberation time with the ear and stop watch method. Remarkably, the uncertainty with the ear and stop watch method was less than 1% when the reverberation times are compared from three different days (with 25 observations each). Sabine concluded from his investigations that the determination of the sound decay with a high precision is very important but remains difficult due to the logarithmic character of the decay curve and the fluctuating sound intensity due to the variation of the interference pattern in the reverberant sound. Finally, he noted that the interior treatment or the color in rooms would outweigh the uncertainties in the measured absorption coefficient values and that the so-called “war of coefficients” would be only a quite meaningless wrangle over practical unessentials in his opinion.

Since the pioneering work of W.C. Sabine and C.F. Eyring much progress has been made. In parallel and surely not independent from acoustic testing, the efficiency and variety of acoustic materials increased rapidly. Unfortunately, this also led to the “battle of the coefficients” due to the diversity in the acoustic values assigned to the same material measured in different laboratories.7 The Acoustical Society was founded in 1929 by four men, among them Paul E. Sabine, because of the “absorption coefficient problem.” At the 10th anniversary meeting of the Society the opening session was dedicated to exactly this ongoing problem. Sabine presented his collected findings from the viewpoint of the testing laboratory and remained positive that the problem could be solved in the future. In the following years important work was carried out: Maa8 derived the distribution of Eigentones for rectangular chambers and Hunt et al.9 analytically showed that modes have to be subdivided into groups having common properties. Kuttruff10 showed that the beginning of the sound decay contains the weighted mean of all decaying modes and should not be disregarded when calculating the reverberation time. Furthermore he showed that the sound decay is curved when plotted on a logarithmic axis and care has to be taken when defining “the” decay slope. Since Eyring's11 contribution on the average sound absorption coefficient at least the battle of the coefficients is resolved and captured in international standards (ISO 354, ASTM C432) but the fighting against uncertainties still remains.12 Recent developments which continue the ideas of former research8–11 include the spatial decomposition of the (decaying) sound field,13 the isotropy of the incident sound field on the absorber,14 and the multi-exponential decay model for calculating decay times.15 In 2029 the 100th anniversary of the ASA will be celebrated with hopefully at least a partial solution to the “absorption coefficient problem.” Let us then open the time capsule from the 25th anniversary celebration16 and see if we satisfied the expectation of our famous pioneers in acoustics.

At the 10th anniversary meeting of ASA Paul E. Sabine5 concluded his presentation with the following statement: “The aim of architectural acoustics is a social one, directed toward the alleviation of the evil of noise and the enhancement of the enjoyment of speech and music. As long as our civilization moves towards social ends, architectural acoustics will continue an important branch of engineering science.” This presently can be regarded as one of the most important aims for acoustic engineers, namely, to design our surroundings to be a little bit more quiet and well-sounding.

1.
P. E.
Sabine
, “
A critical study of the precision of measurement of absorption coefficients by reverberation methods
,”
J. Acoust. Soc. Am.
3
,
12
(
1931
).
2.
P. E.
Sabine
, “
Reverberation measurements of sound absorption coefficients
,”
J. Acoust. Soc. Am.
4
,
38
(
1934
).
3.
P. E.
Sabine
, “
What is measured in sound absorption measurements?
,”
J. Acoust. Soc. Am.
6
,
169
(
1935
).
4.
P. E.
Sabine
, “
The effects of cylindrical pillars in a reverberation chamber
,”
J. Acoust. Soc. Am.
9
,
272
(
1938
).
5.
P. E.
Sabine
, “
Architectural acoustics, its past and its possibilities
,” presented at the
10th Anniversary Meeting of the Acoustical Society of America
,
New York
(May 15,
1939
).
6.
P. E.
Sabine
, “
Measurement of sound absorption coefficients from the viewpoint of the testing laboratory
,” Presented at the
10th Anniversary Meeting of the Acoustical Society of America
,
New York
(May 15,
1939
).
7.
F. V.
Hunt
, “
The absorption coefficient problem
,”
J. Acoust. Soc. Am.
11
,
38
(
1939
).
8.
D. Y.
Maa
, “
Distribution of eigentones in a rectangular chamber at low frequency range
,”
J. Acoust. Soc. Am.
10
,
235
(
1939
).
9.
F. V.
Hunt
,
L. L.
Beranek
, and
D. Y.
Maa
, “
Analysis of Sound Decay in Rectangular Rooms
,”
J. Acoust. Soc. Am.
11
,
80
(
1939
).
10.
H.
Kuttruff
, “
Eigenschaften und Auswertung von Nachhallkurven (Characteristics and analysis of decay curves)
,”
Acustica
8
(
4
),
273
280
(
1958
).
11.
E. F.
Eyring
, “
Methods of calculating the average coefficient of sound absorption
,”
J. Acoust. Soc. Am.
4
,
178
(
1933
).
12.
M.
Vercammen
, “
Improving the accuracy of sound absorption measurements according to ISO 354
,” in
Proceedings of the International Symposium on Room Acoustics,
Amsterdam
,
the Netherlands
(
2019
).
13.
M.
Nolan
,
E.
Fernandez-Grande
,
J.
Brunskog
, and
C.-H.
Jeong
, “
A wavenumber approach to quantifying the isotropy of the sound field in reverberant spaces
,”
J. Acoust. Soc. Am.
143
,
2514
(
2018
).
14.
M.
Berzborn
,
M.
Nolan
,
E.
Fernandez-Grande
, and
M.
Vorländer
, “
On the directional properties of energy decay curves
,” in Proceedings of the 23rd International Congress on Acoustics,
Aachen
,
Germany
.
15.
J.
Balint
,
F.
Muralter
,
M.
Nolan
, and
C.-H.
Jeong
, “
Bayesian decay time estimation in a reverberation chamber for absorption measurements
,”
J. Acoust. Soc. Am.
146
,
1641
(
2019
).
16.
F. A.
Firestone
, “
Anecdotal history of the twenty-fifth anniversary celebration of the Acoustical Society of America
,”
J. Acoust. Soc. Am
26
,
873
(
1954
).