Audio Engineering

Room Acoustics 849

From the graph shown in Figure 29.3 , it can be seen that some pretty heavy constructions
are required in order to achieve good sound separation/insulation. However, it is possible
to also achieve good sound insulation using lightweight materials by using multilayered
construction techniques.

Combinations of layers of plasterboard and softboard, separated by an airspace, are used
frequently. Figure 29.4 shows a typical construction. The softboard is used to damp out
the natural resonances of the plasterboard, which would reduce its sound insulation. The
airspace may also be fi tted with loose acoustic quilting (e.g., fi ber-glass or mineral wool,
to damp out any cavity resonances).

Note that an airtight seal has to be created for optimum sound insulation effi ciency. Also
note that different sized airspaces are used.

A double-leaf construction as shown in Figure 29.4 can achieve a very good level of
sound insulation, particularly at mid and high frequencies.

0

5

10

15

20

25

30

35

40

45

50

55

60

1 10 20 50 100 200 400

Weight (kg/m^2 )

Average sound reduction index (dB)

225 mm

brick-

work

plastered

100 mm stab with

resilient hangers

150 mm

6mm

glass

Hollow core

panel door

150 mm

concrete slab

115 mmbrick workwith 50 mm screed

plastered

100 mm slab with

rigid hangers

100 mm

breeze

plastered

both sides

Staggered stud

with 12 mm

plasterboard

100 mm

breeze

plastered

one side

12 mm

plasterboard with

50 100 studs

100 mm breeze

Solid coretimber door unplastered

12 mm

glass

6mm

glass

6mm

glass

0mm

200 mm

25 mm

wall board

3mm

glass

Figure 29.3 : Sound insulation performance of building materials compared with mass law.