Transmission loss of plasterboard walls

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Transmission loss of plasterboard walls

Northwood, T. D.

C A N A D A

1 I

7

_no.

66

&.NALY

ZED.

by

T.

I3

.

Northwood O F BUlLDFNG R E S E A R C H N A t r O N A L R E S E A R C H C O U N C I L

.

O T T b C A N A D A

TMNSWSSION LOSS O F PLASTERBOARD WALLS

Plasterboard walls constitute an important type of c o n s t r u c t i o n

particularly in modern dwellings, but also in other t y p e s of buildings. Such walls are relatively light, inexpensive, and e a s y t o e r e c t , and they may be

made t o provide adequate fire protection and sound insulation.

Although sound insulation measurements for various plasterboard walls

have been made by various laboratories, they have not, until r e c e n t l y , been

sufficiently well coordinated t o provide an understanding of the effects of various parameters. The purpose of this note is t o present. systematic measurements

on a wide variety of such canstructions. This will provide, f o r immediate u s e ,

up-to-date information on many practical walls obtained by the latest t e s t pro- cedures (ASTM E 9 0 - 6 6 T ) . The main objective, h o w e v e r , is to provide e x -

perimental information f r o m which general conclusians applicable to other

multi-leaf walls may be derived. T h i s note is a complete record of the t e s t

results; another paper analysing the general relations, f r o m empirical and

theoretical viewpoints, is also in preparation.

GENERAL NOTES

A typical plasterboard w a l l consists of two plasterboard leaves

separated by an air space and a system of s t u d s or framing members.

The sound transmission l a s s (TL) of such a wall depends on the T L t s of

the individual leaves and on the degree of coupling introduced by the i n t e r - vening air space and stud system.

It

is found that both the air space and the s t u d s play an important part

in determining the over -all transrnis sion l o s s , and both paths must g e n e r a l l y

be considered when improvements in sound insulation are attempted. Trans

-

mission through the space depends on the internal spacing between wall leaves,

the degree of lateral subdivision of the space, and the amount oi absorption

t r e a t m e n t in the space. Transmission through the studs depends on the

r i g i d i t y of the studs and t h e stud-plasterboard connections; the p r o c e s s may

be thought of as the propagation of flexural vibrations f r o m one w a l l surface to the other by torsion in the studs. If the s t u d s have l o w torsional r i g i d i t y

(e. g , steel channels) transmission via the s t u d s a p p e a r s to be negligible. The effects of various stud and s f x d connection systems are examined in l a t e r

sections.

The performance of the individual heaves of the wall depends on t h e i r surface density {mass per unit area), stiffness, and internal damping.

E X P E R I M E N T A L DETAILS

A l l sound transmission measurements reported here w e r e made in

accordance with ASTM E90

-65T,

"Labor ator y Measurement of Airborne

Sound Transmission L o s s of Building Partitions." A f e w of the simpLer con-

structions, e specially single -leaf walls, have been tested by several l a b o r a -

t a x i e s and the results are found t o be reasonably reproducible. In addition, the transmission loss was calculated f o r some of the single -leaf walls

utilizing theory developed by L. C r e m e r some y e a r s ago. The p a r a m e t e r s r e q u i r e d f o r the calculation are the surface density, modulus of elasticity,

and internal damping of the material. These quantities w e r e determined

f o r plasterboard by static and dynamic experiments on small samples of

p l a s t e r b o a r d ,

The calculations will b e described in d e t a i l in a separate report but

one detail i s worth noting. The basic expression fox transmission ratio

applies t o a train of plane waves reaching the wall at a particular angle of incidence.

T o

obtain the '"random incidence" transmission 10s s , this

e x p r e s s i o n is averaged f o r a uniform distribution of all angles from normal

t o g r a z i n g incidence. Grazing incidence is an u n r e a l i s t i c limit f o r finite

r o o m s and walls and, unfortunately, the calculated result is quite sensitive to this limiting value. S o m e w r i t e r s , noting that s o m e measured

T L

v a l u e s

w e r e about

5

dB higher than calculated random incidence values, have i n f e r r e d t h a t the limiting angle of incidence is about 78 degrees, the so-called ''field incidence" case. The present series of calculations and laboratory measure- ments give the b e s t fit: f o r a limiting angle of 8 5 degrees. It appears,

however, that there can be a spread of about 5 d B among various laboratory

and field measurements, depending an the exact angular distribution of the

incident sound field.

T e s t specimens w e r e mounted in an opening 1 0 f t wide by 8 f t high

separating two r e v e r b e r a t i o n r o o m s . The source room has a volume of

2100 cu f t and the receiving r o o m has a volume of about 9 0 0 0 cu f t . Following

ASTM E 9 0 , each room is equipped with fixed and moving diffusing panels

designed t o provide as good an approximation as possible to the diffuse sound

field that is as s u e d in t r a n s m i s s i o n 10s s theory. The sound pressure l e v e l

in each room i s sampled by a set of nine microphones whose outputs are

observed individually. The variation i s s m a l l enough that a simple arithmetic mean of sound pressure levels i s sufficient to d e t e r m i n e the space-average

sound pressure level in each room. The t e s t signal consists of third-octave

bands of "pink" noise and measurements a r e taken at a s e r i e s of t h i r d - o c t a v e s

c e n t r e d on 1 2 5 t o 4 0 0 0 Hz. In some measurements, the results w e r e extended

to 5000

Hz

to permit a better study of coincidence effects in the high-frequency

PREPAJUTION O F TEST WALLS

The t e s t specimens are described briefly i n the tables or' results, but

a few construction details are elaborated on as folZows,

J o i n t s

Preliminary t e s t s w e r e m a d e with joints between plasterhoard

sheets finished with the conventional tape and joint compound. _{T h e s e}

gave results identical t o those obtained when the joints w e r e simply sealed with masking tape ( s e e Group

I,

W a l l

No.

1 - 2 ) . Most subsequent t e s t s were

done with masking tape on the joints.

Lamination P r o c e d u r e

When two layers (plasterboard or other mate rials) w e r e laminated

together with g y p s u m joint compound, a special applicator w a s used to

apply the compound in a uniform manner i n strips 5/8 in. wide b y 518 in.

high and spaced 1 3/4 in. apart. The second layer of plasterboard w a s

then pressed into place. T e m p o r a r y screws holding the two sheets together

during c u r i n g were removed before t e s t . Two test walls w e r e installed by

a local contractor, using an alternative technique consisting of a few small

patches of joint compound and an extra s e t of permanent s c r e w s driven

through the first sheet into the shkds. In the few instances when contact

cement was used for lamination, it w a s spread over the e n t i r e surfaces.

Space Absorption

Mineral wool or glass f i b r e batts about 2 in. thick or g r e a t e r w e r e

used.

It

was found that the results were not critically sensitive t o thickness

1

or density; a 2-in. glass f i b r e board was slightly l e s s effective as an

a b s o r b e r at l a w frequencies, but similar t o the thick b a k s at high frequencies.

Studs

Canventional 2 x 4 wood studs

11

5/8 b y 3 5 / 8 in. ) w e r e used at 1 6 - and 24-in. spacings. They were s e t i n a 2 x 4 frame around the perimeter

of the t e s t opening, T e s t s conducted without s t u d s utilized the same 2 x 4

p e r i m e t e r frame for supporting the plasterboard. Steel channels 3 518

&.

and 2 s in. wide, spaced at 24-in. c e n t r e s , w e r e mounted in the appropriate

perimeter channel frame, A f e w t e s t s were done also with 1 5/8-in, channels

1

Caulking

T o

avoid problems relating to

leakage

at the perimeter, a bead of caulking compound was applied around the perimeter in every case. _No

attempt was m a d e in

this

study to investigate the efficacy

of

control joints

such as are needed in installations in actual buildings.

Plasterboard

W i t h the ca-operation of several manufacturers, spe cia1 samples

w e r e obtained of gypsum board, representing the extremes of density

and thickness allowed under CSA Standard A8 2.27

-

1963. It was found that within this range there was no measurable difference in performance f o r a particular nominal thickness. Similarly, no difference w a s found between

conventional gypsum board and the so-called Type

X,

fire -resistant

version, Results for vinyl-covered board (vinyl applied o v e r paper) were

c l o s e to those f o r the ordinary paper -covered versions.

RESULTS

The results of aBL the transmission tests included in this s e r i e s

(approximately 100) a r e reported in the attached tables. The t e s t

specimens are arranged in four groups as fallows.

Single -Leaf W a l l s (Table

I)

In

this group are gathered the t e s t results for single layers of

plasterboard and other materials, plus composite constructions consisting

of various sheet materials laminated together. It is hoped that these d a t a ,

together with results f o r two-leaf walls, will provide material f o r testing

any theory applicable to two-leaf walls.

1

Double -Leaf W a l l s , Main Components 2-in. Plasterboard (Table

II)

Included in this group are all the walls in which *-in. p l a s t e r b o a r d

forms the main component of each leaf. W a l l s with additional l a y e r s that

add damping or that affect the s k d - p l a s t e r b o a r d connection are also included. Double-Leaf W a l l s . 5/8-in. Plasterboard (Table

IIIE

Many

of

the s e walls e s s entially duplicate constructions already

described ~JI Table

II,

but f o r f i r e resistance purposes 518-in. plasterboard

1

is g e n e r a l l y more acceptable in practice. As compared to

z-in.

plasterboard,

s u r f a c e density. . Above 1000 H e the coincidence dip with

518-in.

p l a s t e r b o a r d falls about one-third octave below the dip for $-in. board, T h i s results in

slightly poorer high frequency performance.

Included in the t e s t s listed in Table WC were studies of various systems

f o r connecting plasterboard to studs.

Double -Leaf W a l l s E m p l

Different Thicknesses of Plasterboard (Table

IV)

This group includes walls f orrned from different thicknesses of

plasterboard or multiple layers thereof,

For each wall t e s t e d the right-hand portion of the table contains a brief description of the specimen, including the surface d e n s i t y of t h e

wall leaves and, as a single-figure rating, the ASTM Sound T r a n s m i s s i o n

C l a s s . On the left-hand s i d e of the table a r e given the t r a n s m i s s i o n l o s s e s

f o r the standard third-octave frequency bands f r o m 125 to 4000 Hz (in

some instances up to 5000

Hz),

1 . L. G r e r n e r : The Propagation of S t r u c t u r e -Borne Sound. Sponsored

Research (Germany)

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