Handbook for Sound Engineers

76 Chapter 4

general STC range of the gypsum wallboard walls 1 to
8, inclusive.

The three papers by Green and Sherry report
measurements on many wall configurations utilizing
gypsum wallboard.^11 Fig. 4-14 describes three of them
yielding STCs from 56 to 62.

An expression of the empirical mass law stated as an
STC rating rather than transmission loss^10 is shown in
Fig. 4-15. This makes it easy to evaluate the partitions
of Table 4-7 and Fig. 4-14 with respect to partition
surface weight. The numbered STC shaded ranges of
Fig. 4-15 correspond to the same numbered partitions of
Table 4-7, and the A, B, and C points refer to the A, B,
and C constructions of Fig. 4-14. From Fig. 4-15 it can
be seen that the performance of wall types 1 and 9 can

be predicted from the mass law. The other wall types

perform better than what the mass law curve predicts.

This better performance results primarily from decou-

pling one leaf of a structure from the other.

In recent years there have been new developments in

wallboard. QuietRock™*1 is an internally damped wall-

board. Although it is considerably more expensive than

standard gypsum board, it far outperforms conventional

drywall, and for a given STC because less material is

needed when using QuietRock, the cost can be offset.

Following are ten points to remember concerning

frame walls for highest STC ratings:

1. It is theoretically desirable to avoid having the
   coincidence dip associated with one leaf of a wall
   at the same frequency as that of the other leaf.
   Making the two leaves different with coincidence
   dips appearing at different frequencies should
   render their combined effect more favorable.
   However, Green and Sherry found this effect negli-
   gible when partitions having equivalent surface
   weights were compared.^11


2. The two leaves of a wall can be made different by
   utilizing gypsum board of different thickness,
   mounting a soft fiber (sound-deadening) board
   under one gypsum board face and/or mounting
   gypsum board on resilient channels on one side.


3. Resilient channels are more effective on wood
   studs than on steel studs.

Figure 4-14. Three arrangements of gypsum wallboard
two-leaf partitions having progressively higher STC ratings.
(After Green and Sherry, Reference 11.)

2" × 4" studs

16" OC

5/8" Gypsum

wallboard

A. STC 

56

2" × 4"

plate

5/8" Gypsum

wallboard

5/8"

Gypsum

wallboard

1/2" Gypsum

wallboard

2" × 4"

staggered

studs 16" OC

2" × 6"

plate

B. STC 

58

5/8"

Gypsum

wallboard

5/8"

Gypsum

wallboard

3 5/8"

steel studs

24" OC

3 5/8"

steel

runners

space 1"

C. STC 

62

Figure 4-15. A variation of the empirical mass law

expressed in terms of sound transmission class rather than

TL. The numbers refer to the partitions of Table 4-7; the

letters refer to Fig. 4-14.

1*QuietRock copyright Quiet Solution, 125 Elko Dr.,

Sunnyvale, CA, 94089.

Partition surface density–lb/ft^2

0.3 1 5 10 50 100

70

60

50

40

30

20

Sound transmission class (STC)^10

Empirical

mass law

7

5

3

4

6

A

B

C 10

9

8

1