spacer spacer Go to Kaye and Laby Home spacer
spacer
spacer spacer spacer
spacer
spacer
spacer
spacer spacer

You are here:

spacer

Chapter: 2 General physics
    Section: 2.4 Acoustics
        SubSection: 2.4.4 Building acoustics

spacer
spacer

spacer

« Previous Subsection

Next Subsection »

Unless otherwise stated this page contains Version 1.0 content (Read more about versions)

2.4.4 Building acoustics

The sound absorption coefficient of a material is α = (1 − r), where r, the sound energy reflection coefficient, is the ratio of sound energy reflected from the surface of the material to that incident upon it. Values for a specific material depend upon frequency and upon the angle of incidence of the sound. When the sound field is approximately diffuse the corresponding quantity is denoted by αs; this may be determined in accordance with BS 3638:1987. The values in the table overleaf have been taken from Evans and Bazley (1978) which predates the current standard. Absorption depends on mounting and other details of construction and the following values should be regarded only as typical.




Reverberation absorption coefficients

Material

Thickness
(mm)

Frequency/Hz

125

250

500

1000

2000

4000

Acoustic plaster   .  .  .  .  .  .  .  .  .  .  .  .

13

0.15

0.20

0.35

0.60

0.60

0.50

Acoustic tiles (perforated fibreboard) .  .

18

0.10

0.35

0.70

0.75

0.65

0.50

Asbestos (sprayed).  .  .  .  .  .  .  .  .  .  .

25

0.10

0.30

0.65

0.85

0.85

0.80

Brickwork    .  .  .  .  .  .  .  .  .  .  .  .  .  .

0.02

0.02

0.03

0.04

0.05

0.07

Carpet (Axminster)  .  .  .  .  .  .  .  .  .  .

  8

0.05

0.15

0.30

0.45

0.55

Carpet on underlay  .  .  .  .  .  .  .  .  .  .

14

0.05

0.20

0.40

0.60

0.65

Curtain (velour, draped)   .  .  .  .  .  .  .

0.14

0.35

0.55

0.72

0.70

0.65

Glass fibre (resin-bonded)  .  .  .  .  .  .

25

0.10

0.25

0.55

0.70

0.80

0.85

Glass wool (uncompressed) .  .  .  .  .

25

0.10

0.25

0.45

0.60

0.70

0.70

Mineral wool  .  .  .  .  .  .  .  .  .  .  .  .

25

0.10

0.25

0.50

0.70

0.85

0.85

Polystyrene, expanded (rigid backing)

13

0.05

0.05

0.10

0.15

0.15

0.20

Polystyrene, expanded (on 50 mm battens)

13

0.05

0.15

0.40

0.35

0.20

0.20

Polyurethane foam (flexible)

50

0.25

0.50

0.85

0.95

0.90

0.90

Snow  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .

25

0.15

0.40

0.65

0.75

0.80

0.85

Wood panelling (oak, on 25 mm battens)

13

0.20

0.10

0.05

0.05

0.05

0.05



Insulation against airborne noise. The sound reduction index (R) is the ratio of sound energy incident on a partition to that which is transmitted through it, expressed in decibels (BS 2750: 1980). The values vary with frequency and angle of incidence; for comparative purposes a single value (Rw) can be derived from the data over the frequency range 100–3150 Hz according to BS 5821: Part 1: 1984. Although mass is the main determinant of R above the resonant frequency, the relationship is not a simple one, due to ‘coincidence’ effects associated with flexural waves in the partition (Fahy 1985). For single, homogeneous partitions, however, the mean value of R over the range 100–3150 Hz can be estimated to be approximately Ravg =10 + 15 log10(m) dB, where m is the surface mass density in kg m−2. For some types of partition RwRavg + 3 dB. The table opposite gives laboratory values of R and Rw obtained at the Building Research Establishment and the Building Test Centre of British Gypsum Ltd (Dr L. C. Fothergill, private communication).




Sound Reduction Indices (dB)

 

Type of element

Mass

kg/m2

1

 Octave Band Centre Frequency/Hz

3

Rw
dB

100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

1

Thermal double glazing

22

23

19

17

21

26

28

30

32

33

33

32

30

28

30

33

30

 

(6-12-6), timber frame

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2

As 1, plus 4 mm secondary pane

35

30

31

27

32

38

40

44

47

49

49

44

41

43

43

45

42

 

spaced 150 mm, reveal lined

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

with absorbent

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3

Brick, 100 mm thick, no finish

200

33

35

33

34

34

33

36

39

42

44

46

48

49

51

52

53

44

4

Lightweight aggregate

260

15

13

15

15

14

15

17

17

19

20

22

23

27

28

31

37

22

 

blockwork 215 mm thick, no

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

finish (permeable block)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

As 4 with plaster finish both

280

36

31

33

35

38

42

47

49

52

55

59

61

63

65

66

67

51

 

sides

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6

Two leaves 100 mm blockwork,

390

28

27

31

33

35

35

41

42

47

52

55

59

63

66

69

70

46

 

50 mm cavity, no finish

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7

As 6 with plaster finish both

410

41

37

37

38

38

41

46

49

54

59

63

67

72

76

79

82

52

 

sides

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

Two leaves 100 mm aerated

133

35

40

44

44

43

42

42

41

44

49

53

58

61

64

66

71

50

 

concrete blockwork, 50 mm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

cavity, no finish

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

9

As 8 with plaster finish both

153

37

42

46

43

38

38

40

43

47

51

56

60

66

68

71

76

49

 

sides

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10

Floor–18 mm chipboard

19

15

20

25

28

29

34

37

37

42

43

44

44

42

40

41

38

 

194 × 45 mm joists at 450 mm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

centres, 12.5 mm plasterboard

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ceiling

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

11

As 10 but 600 mm joist spacing

17

26

32

38

35

35

37

37

41

45

47

49

51

49

45

40

42

12

12.5 mm plasterboard sheet

11.8

21

21

23

25

25

26

28

28

29

31

33

34

35

35

29

26

31

13

12.5 mm plasterboard each side

 

17

18

27

37

34

27

35

33

37

37

42

46

48

49

46

38

38

 

of 75 mm × 38 mm timber studs

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

14

As 13 with 25 mm mineral wool

 

13

15

28

35

31

32

37

37

42

43

47

50

53

53

46

41

40

 

in cavity

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

15

As 14 with no layers of

 

24

24

33

42

35

37

42

44

47

48

51

54

57

58

52

48

46

 

plasterboard each side

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

16

Two leaves of 12.5 mm + 19 mm

 

43

47

55

56

59

64

67

71

72

72

75

80

83

84

86

86

70

 

plasterboard on metal studs,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

separated by 250 mm cavity

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

with 100 mm mineral wool

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 




References

BS 2750: Part 3: 1980 Laboratory measurements of airborne sound insulation of building elements, equivalent to ISO 140/111–1978.
BS 3638: 1987 Measurement of absorption in a reverberation room, equivalent to ISO 354-1985.
BS 5821: Part 1: 1984 Rating the sound insulation in buildings and of building elements, equivalent to ISO 717/1-1982.
E. J. Evans and E. N. Bazley (revised 1978) Sound Absorbing Materials, NPL ISBN 0 9504496 3 6.
F. Fahy (1985) Sound and structural vibration, Academic Press.

D.R.Bacon

« Previous Subsection

Next Subsection »

spacer


spacer
spacer
spacer spacer spacer

Home | About | Table of Contents | Advanced Search | Copyright | Feedback | Privacy | ^ Top of Page ^

spacer

This site is hosted and maintained by the National Physical Laboratory © 2014.

spacer