Audio Engineering

Acoustic Environment 103

The refl ected energy is 1 a.

Table 3.4 gives typical absorption coeffi cients for common materials. These coeffi cients
are used to calculate the absorption of boundary surfaces (walls, fl oors, ceilings, etc.).

Table 3.4 : Sound Absorption Coeffi cients of General Building Materials and Furnishings

Materials Coeffi cient

125 Hz 250 Hz 500 Hz 1 kHz 2 kHz 4 kHz

Acoustical plaster ( “ Zonolite ” )

½-in.-thick trowel application

1-in.-thick trowel application

0.31

0.25

0.32

0.45

0.52

0.78

0.81

0.92

0.88

0.89

0.84

0.87

Acoustile, surface glazed and perforated

structural clay tile, perforate surface

backed with 4-in. glass fi ber blanket of 1

lb/ft^2 density

0.26 0.57 0.63 0.96 0.44 0.56

Air (Sabins per 1000 ft^3 ) 2.3 7.2

Brick, unglazed 0.03 0.03 0.03 0.04 0.05 0.07

Brick, unglazed, painted 0.01 0.01 0.02 0.02 0.02 0.03

Carpet, heavy

On concrete

On 40-oz hairfelt or foam rubber with

impermeable latex backing

On 40-oz hairfelt or foam rubber

0.02

0.08

0.06

0.24

0.14

0.57

0.37

0.69

0.60

0.71

0.65

0.73

40-oz hairfelt or foam rubber 0.08 0.27 0.39 0.34 0.48 0.63

Concrete block

Coarse

Painted

0.36

0.10

0.44

0.05

0.31

0.06

0.29

0.07

0.39

0.09

0.25

0.08

Fabrics

Light velour, 10 oz/yd^2 , hung straight in

contact with wall

Medium velour, 10 oz/yd^2 , draped to

half area

Heavy velour, 18 oz/s yd^2 draped to half

area

0.03

0.07

0.14

0.04

0.31

0.35

0.11

0.49

0.55

0.17

0.75

0.72

0.24

0.70

0.70

0.35

0.60

0.65

(Continued)