Handbook for Sound Engineers

Acoustical Noise Control 79

Another means of decoupling the floor above from
the sound room ceiling involves suspending the entire
ceiling by a resilient suspension, such as in Fig. 4-19.
Mason Industries, Inc. reports one test that demonstrates
the efficacy of this approach.^13 They started with a
3 inch concrete floor that alone gave STC-41. With a
12 inch air gap, a^5 e 8 inch gypsum board ceiling was
supported on W30N spring and neoprene hangers,
resulting in STC-50. By adding a second layer of^3 einch
gypsum board and a sound-absorbent material in the air
space, an estimated STC-55 was realized. The W30N
hanger uses both a spring and neoprene. This combina-
tion is effective over a wide frequency range. The
spring is effective at low frequencies and the neoprene
at higher frequencies.

4.3.7 Floor Construction

Many variables must be considered when designing

isolated floors. These variables include cost, load limits

of the existing structure, the desired isolation, and the

spectrum of the noise. Every successful system uses a

combination of mass and resilient support designed to

work above the resonance point of the system, and thus

achieve isolation. There are three general approaches to

floating or isolated floors; the continuous underlayment,

the resilient mount, and the raised slab, Fig. 4-20.

Floating Floors. Once again, simply increasing mass is

often the least productive way to make significant gains

in STC. For example, a 6 inch solid concrete floor has

an STC of 54, and doubling the thickness to 12 inches

Table 4-8. Floor and Ceiling Systems

Ceiling Treatment Treatment of Floor Above Sound

Transmission

Class*

2 inch gypsum wallboard nailed to joists 12 inch lightweight concrete on e inch plywood, 2

× 12 joists 16 inches on centers

STC-48

3 inch mineral wool. Resilient channels 2 ft-0 inch on center

2 inch sound deadening board, einch gypsum board

1 cinch plywood on 2 × 10 joists 16 inches oc STC-46

3 inch mineral wool. Resilient Channels 2 ft-0 inch oc einch

gypsum board

12 inch lightweight concrete on 2 inch sound deadening

board on einch plywood, 2 × 10 joists, 16 inches oc

STC-57

2 inch mineral wool. 2 inch sound deadening board. Resilient

channels 2 ft-0 in oc e in gypsum board

12 inch lightweight concrete on einch plywood, 2 × 10

joists, 16 inches oc

STC-57

*These are FSTC ratings.^9

Figure 4-19. A method of suspending a ceiling that gives a

great improvement in STC rating of the floor and ceiling

combination.

Fiberglass or neoprene and

spring hangers

Two layers^5 / 8 " gypsum board

Figure 4-20. The dramatic improvement of sound transmis-

sion class (STC) from 54 to 76 by adding a 4 inch floating

floor with a 1 inch air gap between it and the structural

floor. (Riverbank TL-71-247 test reported by Mason Indus-

tries, Inc., in Reference 13.)