We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
March, 1950
GLOVER AND MCLAREN \ ACOUSTICS
75
Table of Time Factors for
Optimum Reverberation
Multiplier
Frequency c/s.
Multiplier
Multiplier
Speech
Speech
Music
and Music
64
1.75
2.30
2.03
128
1.38
1.55
1.47
256
1.15
1.20
1.18
512
1.00
1.00
1.00
1,024
1.00
1.00
1.00
2,048
1.00
1.00
1.00
4,096
1.14
1.04
1.09
8,192
1.35
1.15
1.25
16,384
1.60
1.35
1.47
It is interesting to note that all curves indicate an increase in reverberation as desirable at the highest and lowest frequencies.
Too much reverberation at the lower frequencies causes an unnatural booming effect, whilst an increased reverberation at the higher frequencies, although desirable from the point of view of intelligibility in speech, is not desirable in music. Whenever there is a tendency for an increased reverberation in the higher frequencies, the acoustical properties of the room are regarded as unpleasant, and musicians dislike the hard tone which is imparted.
Experience seems to indicate that intermediate curves such as those indicated in heavy lines, and marked " Music " and " Speech," in Fig. 1 provide the most desirable reverberation characteristics. The " datum " of time on this figure is for 512 c/s., for which frequency the optimum time is taken as unity.
To find the optimum time at any other frequency it is only necessary to multiply by the appropriate time factor read off from the graph, or taken from the appended table.
The importance of the careful selection of absorbents to give optimum reverberation throughout the frequency range is emphasised in the tabulated results of suggested treatments for a faulty auditorium.
Although each of the suggested treatments gives optimum reverberation at 512 c/s, treatments B and C show considerable departure therefrom, at other frequencies, and the room, if treated by these methods, would be satisfactory for the soprano voice, but too reverberant for the bass, and too " dead " for the piccolo.
Table Showing Selective Absorption of Room Corrected by Treatment with :
A. 1,420 sq. ft. of Insulite.
B. 835 sq. ft. of Cotton fabric draperies (14 oz. per sq. yard) in very heavy folds.
C. 573 sq. ft. of " BB " Acousti-Celotex.
Mean
Source of Sound
Frequency
Reverberation Time
A
B
C
Bass Voice
128
1.22 sec.
3.72 sec.
2.01 sec.
Trombone and Tenor
256
1.14 sec.
1.46 sec.
1.50 sec.
Clarinet and Soprano
512
1.00 sec.
1.00 sec.
1.00 sec.
Violin and Flute
1,024
0.85 sec.
0.64 sec.
0.95 sec.
Piccolo
2,048
0.81 sec.
0.77 sec.
0.92 sec.