|New Data for Acoutiscal Properties of
An environmental acoustics research report in which seven laboratories
from Canada and the United States participated is the basis for
a revision of ASTM E 477, Standard Test Method for Measuring Acoustical and Airflow Performance
of Duct Liner Materials and Prefabricated Silencers. The revised
standard will provide a better understanding of the acoustical
properties of duct-silencers installed in ventilation systems
to reduce air-conditioning noise.
Data from the interlaboratory study supports a revised precision
statement for Standard E 477 that extends to a 63 Hertz octave
band. It will be included in a revision of E 477 by a task group
of ASTM Subcommittee E33.08 on Sound Transmission in Committee
E33 on Environmental Acoustics that will be reviewed and re-published
by the Society.
A well-known test originated in 1973 by ASTM, E 477 is referenced
in building codes, and has been adopted by the U.S. Department
of Defense and approved by the American National Standards Institute.
The precision statement covers both insertion loss and generated
noise of silencers.
It is a summary of a very extensive series of round robins that
took five years and gives us a rational basis for the precision
and reproducibility of E 477 data, said the subcommittee chair,
Howard Kingsbury, P.E., acoustical consultant, State College,
Pa. Recently, the standard has been extended down in frequency
range to include the 63 Hertz octave band. This is the first time
anybody has ever looked extensively at such low frequency data
obtained in a variety of reverberation rooms.
The round-robin tests included a 3 ft.-long standard pressure-drop
silencer, a 7-ft. long high-insertion loss silencer, and a 5-ft.
long packless (no fiber-fill) silencer, he explained, pointing
to the wide of range of silencer-types evaluated.
As stated in the standard, E 477 covers the laboratory testing
of duct-liner materials, integral ducts, and in-duct absorptive
silencers. Procedures describe measures of acoustical insertion
loss, airflow generated noise, and pressure drop as a function
of airflow. A provision is included for a simulated semi-reflective
plenum to fit around thin-walled duct and silencer test specimens,
as the acoustical environments around such thin-walled specimens
can affect the measured insertion loss.
For further technical information, contact Howard Kingsbury, P.E., State College, Pa. (phone/fax: 814/238-9688). Committee
E33 meets April 9-10 in West Conshohocken, Pa. For meeting or
membership details, contact Staff Manager Steve Mawn, ASTM (phone: 610/832-9726). //
Copyright 2001, ASTM