Sound transmission analysis by sound intensimetry.
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Date
1985
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Abstract
This thesis represents the development and evaluation of a theory for
sound transmission analysis by sound intensimetry. In the context of
this study sound transmission analysis is understood to embrace the
following:
(1) The measurement of sound reduction indices.
(2) Diagnostic analysis of sound transmission through panels and
structures.
The sound intensity method is examined against the theoretical background
of the classic two-room method which forms the basis of currently
used international standards. The flanking problem, which is one of
the principle limiting factors in the use of the classic method, is
analyzed.
The standard formulation of the intensity method is expanded to account
for leakage error, boundary interference effects and calibration mismatch.
It is shown that the commonly observed low-frequency discrepancy
between intensity and classic method results is resolved by application
of the Waterhouse correction.
Sound absorption by the test object on the receiving side is shown to
cause an error which increases with the flanking factor and with the
fraction of the receiving room absorption located on the surface of the
test object. Guidelines are developed for the assessment and control
of absorption error in practical situations.
Using the common mode rejection index as a performance rating for sound
intensity meters, the measurement of sound transmission in reactive
fields is investigated. Derivation of a formula for the reactivity
near the surface of a transmitting panel surrounded by a flanking
structure in a reverberant field, leads to the development of a theoretical
framework and criteria for the planning and evaluation of test
arrangements for sound transmission analysis. Guidelines are given for
the calculation of minimum receiving room absorption and the microphone
spacing required in practical situations.
A study of the characteristic properties of sound intensity fields in
diffuse and non-diffuse environments is used as a basis in formulating
a new method of measuring directional diffusivity. Based on the relationship
between reactivity and the degree of directional balance in a
sound intensity field, this method involves spatial averaging of the
pressure level and determination of the magnitude of the total
intensity vector at the point under consideration. A direct-reading
diffusivity meter has been developed and employed in assessing
diffusivity in practical situations.
The effect of a lack of directional diffusivity on the accuracy of
sound transmission analysis in reactive fields is examined. Criteria
for calculating minimum diffusivity requirements in the source and receiving
room are developed and evaluated experimentally.
Description
Thesis (Ph.D.)-University of Natal, 1985.
Keywords
Sound--Transmission., Sound--Measurement., Theses--Physics.