Evaluations of new speech security quick test

Abstract

This report presents extensive laboratory measurements to evaluate a new speech security quick test intended to provide accurate estimates of the results of the full speech security test (ASTM E2638-08). Ce rapport fait état de mesures en laboratoire exhaustives qui ont été réalisées dans le but d'évaluer un nouvel essai rapide de la confidentialité des entretiens permettant d'estimer avec précision les résultats de l'essai complet suivant la norme ASTM E2638-08. RES

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http://irc.nrc-cnrc.gc.ca
Evaluations of new speech sec urity
quick test
RR-279
B r a d l e y , J . S . ; G o v e r , B . N .

March 31, 2009














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Evaluations of
New Speech Security Quick Test






J.S. Bradley and B.N Gover












IRC Report RR-279
31 March 2009

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Summary
This report presents extensive laboratory measurements to evaluate a new speech security
quick test intended to provide accurate estimates of the results of the full speech security
test (ASTM E2638-08). The proposed new quick test procedure would measure level
differences from a calibrated source on one side of a wall to a spot receiver 0.25 m from
the other side of the wall as illustrated in Fig. A.
The measurement results in
this report evaluated the effects
of various parameters on the
results of the quick test
procedure and compared them
to those obtained using the full
speech security test. The
comparisons included
measurements of a typical wall
construction and the same wall
with 2 variations of a door
included. The tests also
included systematic variations
of the sound absorption in the
test rooms.
The quick test procedure
resulted in lower measured
level difference values than the
full test procedure and the differences varied with the amount of room absorption.
However, the differences did not vary greatly over frequency and this was particularly
true when a dodecahedron loudspeaker was used.
h
ds
dm
test wall
microphone
loudspeaker
Fig. A. Source and receiver positions for the new
quick test procedure.
By correcting for the effects of room absorption, it was possible to provide quite accurate
predictions of the level differences (LD), averaged over frequency, obtained from the full
test. For tests using a dodecahedron loudspeaker, the RMS difference between the
predicted and measured LD(avg) values was only 0.56 dB, which increased to 1.46 dB
when a directional source was used.
Differences between the two measurement approaches can be larger at individual 1/3-
octave band frequencies, but agreement was again better for predictions from quick test
measurements made using a dodecahedron loudspeaker. Fig. B illustrates the agreement
possible between predicted and measured level differences for the wall-with-no-door
construction in the upper panel and for the wall-with-a-door in the lower panel. For the
constructions and room absorption conditions tested, the RMS differences of the 1/3-
octave band measurements varied between 1 and 2 dB depending on the loudspeaker
type, construction details and room absorption.
Additional investigations showed that another variation the quick test approach could be
applied to measuring the sound transmission loss characteristics of installed doors in field
situations. Since doors and door seals are often the source of speech security problems, a
more efficient means of assessing their performance could be practically very useful.

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250500100020004000
0
10
20
30
40
Wall with Door
Predicted Pos. #5
Measured Pos. #5

LD(f), dB
Frequency, Hz
20
30
40
50
60
Wall No Door
Predicted Pos. #5
Measured Pos. #5


LD(f)
Fig. B. Example comparisons of predicted and
measured full test LD(f) values for a wall with
no door (upper) and for a wall with a door
(lower).
It was also demonstrated that impulse
response measurement software could be
adapted to provide a more efficient but
equally accurate approach to making
quick test measurements. With the
ability to provide immediate results, this
approach could be a useful tool for
assessing and diagnosing speech security
problems in situ.
Evaluations of the quick test procedure
for a broader range of combinations of
doors and walls are required to more
generally establish the accuracy of the
approach.


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