Building Design and Construction Handbook - Merritt - Ventech!

11.162 SECTION ELEVEN
acoustical ceiling as a sound barrier. Performance data for most typical commercial
ceilings are published in various bulletins and advertising matter.
11.80 ACOUSTICAL PERFORMANCE DATA
To simplify and standardize evaluation of the acoustical performance of materials
and systems, various rating systems have been adopted. The best known and most
widely used are those published by ASTM, 1916 Race St., Philadelphia, PA 19103.
Partitions, Floor-Ceiling Assemblies, and Barriers. Insulation (or isolation) of
airborne sound provided by a barrier is usually expressed as its sound transmission
class (STC). For a specific construction, STC is determined from a soundtransmission-loss
curve obtained from a standardized test of a large-scale specimen.
This curve is compared with a standard contour, and a numerical rating is assigned
to the specimen (ASTM E90 test procedure and ASTM E413, Determination of
Sound Transmission Class).
Table 11.27 lists typical STC ratings of several partition, wall, and floor-ceiling
components or assemblies. Published data for almost any type of construction can
be obtained from various sources.
A difference of one or two points between two similar constructions is rarely
significant. Normally, constructions tend to fall into groups or classes with their
median values about five points apart. In Table 11.28, the italic number represents
the median of a performance group which includes the numbers on either side of
the median.
The impact insulation (or isolation) provided by floor-ceiling assemblies is usually
expressed as their impact noise rating (INR) or impact insulation (IIC). Like
STC, INR and IIC values are obtained by comparing the curve of the sound spectrum
obtained in a test with a standard contour (except that for INR and IIC the
sound pressure level is measured in the room below the noise source). The entire
procedure is controversial and far from widely accepted; but its use is so widespread
that designers and builders should be aware of it. (See ASTM RM 14-4.)
Table 11.29 lists the impact isolation provided by several types of construction.
Note particularly the enormous effect of certain floor coverings on the performance
of the construction. (While IIC values are shown in Table 11.29, they can be converted
to INR values by subtracting 51 points; for example, IIC 60 � INR 9, and
IIC 45 � INR �6, etc.)
TABLE 11.28 STC Performance Groups
30 31 32 33 34
35 36 37 38 39
40 41 42 43 44
45 46 47 48 49
50 51 52 53 54
55 56 57 58 59