THEORETICAL ANALYSIS OF LINED -DUCT SOUND ATTENUATION
AbstractThis paper investigates theoretically how duct geometry and liner thickness affect the attenuation of fundamental-mode
sound propagation in a lined duct. The study was done to satisfy the need for a greater understanding of interior natural-
ventilation openings and of silencers implemented to improve the acoustical performance (‘ventilators’), and to provide
engineers and architects with optimal-design guidelines. It assumed ventilators of the simplest form – straight, acoustically-
lined ducts of rectangular cross-section. An analytical solution is presented for the attenuation of the fundamental mode in
such a duct. Duct-liner thickness does not affect high-frequency performance; however, it limits low-frequency performance.
A 25-mm liner is likely not thick enough to be effective, but a 100-mm liner may be excessive. Increasing the duct height
reduces the attenuation at all frequencies; in order to provide effective attenuation through the 4000-Hz band, the height
should not exceed 100 mm. If the cross-sectional aspect ratio of a duct is greater than 10, or the duct is only lined on two
opposing surfaces, the attenuation of its fundamental mode is in effect identical to that of a 2D lined duct. Provided that the
duct liner and height are such that the silencer is effective at absorbing sound at a given frequency, reducing the aspect ratio
towards unity will result in large attenuation gains.
How to Cite
Copyright on articles is held by the author(s). The corresponding author has the right to grant on behalf of all authors and does grant on behalf of all authors, a worldwide exclusive licence (or non-exclusive license for government employees) to the Publishers and its licensees in perpetuity, in all forms, formats and media (whether known now or created in the future)
i) to publish, reproduce, distribute, display and store the Contribution;
ii) to translate the Contribution into other languages, create adaptations, reprints, include within collections and create summaries, extracts and/or, abstracts of the Contribution;
iii) to exploit all subsidiary rights in the Contribution,
iv) to provide the inclusion of electronic links from the Contribution to third party material where-ever it may be located;
v) to licence any third party to do any or all of the above.