1.1 This Standard adopts insertion loss—the difference
between acoustical levels before and after
a noise-barrier installation—as the basis for evaluating
the acoustical effectiveness of an outdoor
noise barrier. Methods are provided to determine
the insertion loss of outdoor noise barriers at selected
receiver locations and under conditions of
interest.
1.2 This Standard covers insertion loss determination,
by measurement or by the combination of
measurement and prediction, for outdoor noise
barriers of all types. Sound sources at a site may
be those that are naturally present, controlled
natural sound sources, or controlled artificial
sound sources. Preferred acoustical descriptors
are time-average, A-weighted sound level, Aweighted
sound exposure level, or octave-band
sound pressure level. Other acoustical descriptors
of the BEFORE and AFTER sound are not precluded.
1.3 Standardized receiver locations or measurement
conditions are not prescribed. Measured insertion
losses apply only for the stated conditions
and are not to be generalized to represent other
conditions, sites, receiver locations, or sound
sources.
1.4 This Standard may be used for routine
checking of the insertion loss of an outdoor noise
barrier, or for engineering or diagnostic evaluations.
The methods of the Standard may be used
in situations where a barrier is to be installed, or
has already been installed.
1.5 This Standard does not present methods for
comparing the insertion loss of outdoor noise barriers
at different sites, nor does it specifically address
sound transmission loss through a barrier.
While comparisons of the insertion loss of outdoor
noise barriers at different sites or extrapolations to
other conditions may be possible, such comparisons
or extrapolations are not within the scope of
this Standard.
1.6 Reliable and repeatable results may be expected
when the distances between all receivers
and their closest and strongest sound sources (or
closest point of approach for mobile sound
sources) are within 70 m. The methods of the
Standard may be applied for other conditions, but
the experimental uncertainties likely will increase,
perhaps substantially.
1.7 This Standard presents two methods for indirectly
determining the level of the BEFORE
sound. The two methods are (1) by measurement
at a second site that is equivalent to the desired
site prior to installation of the barrier, or (2) by prediction
of the BEFORE sound levels. Equivalence
here is in terms of sound-source characteristics,
receiver locations, and terrain, atmospheric, and
ground conditions. The Standard presents principles,
not procedures, for assessing soundsource,
atmospheric and terrain equivalence, as
well as for choosing a model to predict the level of
BEFORE sound.
1.8 This Standard presents a method to determine
a lower bound to the insertion loss when
background noise prevents clear measurement of
the source sound level at a receiver location. In
many applications, reporting a barrier insertion
loss for a given receiver location as ‘‘equal to or
greater than X dB’’ is sufficient. This Standard also
presents a method to determine the total experimental
uncertainty associated with the barrier insertion
loss.
1.9 Because of many factors affecting the sound
levels at receiver locations, it may not be possible
to determine the insertion loss of an outdoor noise
barrier for conditions of interest.
ASA S12.8-1998 Referenced Document
ANSI S1.26-1995 Method for the Calculation of Absorption of Sound by the Atmosphere
ANSI S1.43-1997 Specifications for Integrating-Averaging Sound Level Meters
ASA S12.8-1998 history
1998ASA S12.8-1998 METHODS FOR DETERMINING THE INSERTION LOSS OF OUTDOOR NOISE BARRIERS