Handbook for Sound Engineers

74 Chapter 4

4.3 Isolation Systems

Isolation systems must be dealt with holistically. One
must consider walls, ceilings, floors, windows, doors,
etc. as parts of a whole isolation system. Vibration takes
every path possible when traveling from one spot to
another. For example, if one intends to build a sound
room directly below a bedroom of another tenant in a
building, one might assume that special attention must
be paid to the ceiling. Of course this is correct. However,
there are often paths that would permit the vibration to
bypass the ceiling. All these flanking paths must be
accounted for if isolation between two spaces is desired.

It should be noted that in some parts of the country
(most notably California) building codes require
seismic engineering. Make sure that the isolation
systems that are under consideration do not violate any
local seismic codes or require additional seismic
restraints. Mason Industries has published a bulletin that
is quite instructive in seismic engineering.^11

4.3.1 Wall Construction

Acoustic partitions are complex entities. As was previ-
ously noted, walls exhibit different degrees of isolation
in different segments of the spectrum. It is therefore
imperative that you know what frequencies you are
isolating. (Refer to Fig. 4-8.) The more massive the wall
and the more highly damped the material, the fewer the
problems introduced by diaphragmatic resonance. In
comparing the relative effectiveness of various wall
configurations, the mass law offers the most easily
accessible rough approximation. However, most prac-
tical acoustical partitions actually perform better—that
is, they achieve more loss—than what is predicted by
the mass law. To assist in the computation of isolation
based on mass, the densities of various common
building materials are listed in Table 4-6. If an air space
is added as in double wall construction, this introduces

an element other than mass and generally leads to

higher transmission loss.

4.3.2 High-Loss Frame Walls

The literature describing high TL walls is extensive.

Presented here is a dependable, highly simplified over-

view of the data with an emphasis on practical solutions

for sound room walls. Jones’s summary shown in Table

4-7 describes eight frame constructions including the

STC performance of each.^7 In each of these construc-

tions Gypsum wallboard is used because it provides an

inexpensive and convenient way to get necessary wall

mass and as fire retardant properties. Two lightweight

concrete block walls, systems 9 and 10, fall in the

Figure 4-13. The sound barrier attenuation required for the
sound room example of Fig. 4-12 is specified here as
STC-47.

Needed reduction

32 63 125 200 500 800 2k 5k 8k

60

55

50

45

40

30

25

20

15

10

Frequency–Hz

SPL–dB STC

Table 4-6. Building Material Densities

Material (inches) Density (lb/ft^3 ) Surface Density (lb/ft^2 )

Brick 120

44 0.0

88 0.0

Concrete: light wt. 100

43 3.0

12 100.0

Concrete: dense 150

45 0.0

12 150.0

Glass 180

¼3.8

½7.5

¾11.3

Gypsum wall-

board

50

½2.1

2.6

Lead 700

3.6

Particle Board 48

¾1.7

Plywood 36

¾2.3

Sand 97

18 .1

43 2.3

Steel 480

¼10.0

Wood 24–28

1 2 .4

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