[georgia]

Wallace Clement Sabine (1868-1919)

Sabine's Reverberation Formula
Wallace Clement Sabine was a pioneer in architectural acoustics. A century ago he started experiments in the Fogg lecture room at Harvard, to investigate the impact of absorption on the reverberation time. It was on the 29th of October 1898 that he discovered the type of relation between these quantities. Sabine derived an expression for the duration T of the residual sound to decay below the audible intensity, starting from a 1,000,000 times higher initial intensity:

T = 0.161 V/A

where V is the room volume in cubic meters, and A is the total absorption in square meters. Sabine's reverberation formula has been applied successfully for many years to determine material absorption coefficients by means of reverberation rooms. Keeping in mind some conditions with regard to the sound field diffusion and the value of A, Sabine's formula is still widely accepted as a very useful estimation method for the reverberation time in rooms.

Sabin as Unit of Sound Absorption
The unit of sound absorption is square meter, referring to the area of open window. This unit stems from the fact that sound energy travelling toward an open window in a room will not be reflected at all, but completely disappear in the open air outside. The effect would be the same if the open window would be replaced with 100 % absorbing material of the same dimensions.


Therefore, 1 square meter of 100 % absorbing material has an absorption of 1 square meter of open window. In honor of W.C. Sabine, the unit of absorption is also named sabin or metric sabin. However, these units are used not very often. One sabin is the absorption of one square foot of open window, and one metric sabin is the absorption of one square meter of open window.


Sabine Units of Common Materials (Given Per Square Foot or Per Unit)
Material
125Hz 250Hz 500Hz 1kHz 2kHz 4kHz

Carpet - heavy on concrete
0.02 0.06 0.14 0.37 0.60 0.65

Carpet - heavy on 40oz hair felt
0.08 0.24 0.57 0.69 0.71 0.73

Carpet - heavy with latex backin on foam or 40hz weave
0.08 0.27 0.39 0.34 0.48 0.63

Carpet- outdoor/indoor
0.01 0.05 0.10 0.20 0.45 0.65

Wood Floor
0.15 0.11 0.10 0.07 0.06 0.07

Concrete Floor
0.01 0.01 0.015 0.02 0.02 0.02

Linoleum, Asphalt-tile, or cork tile on concrete
0.02 0.03 0.03 0.03 0.03 0.02

Foam backed carpet on concrete
0.05 0.16 0.44 0.70 0.60 0.40

Heavy carpet + heavy foam underlay on concrete
0.15 0.25 0.50 0.60 0.70 0.80

Vinyl flooring
0.03 0.04 0.05 0.04 0.05 0.05

Gypsum board: 1/2" on 2 x 4s, 16" on centers (plasterboard)
0.29 0.10 0.05 0.04 0.07 0.09

9mm Plasterboard over 20mm air gap
0.30 0.2 0.15 0.05 0.05 0.05

Plaster, gypsum or lime smooth finish on tile or brick
0.013 0.015 0.02 0.03 0.04 0.05

Plaster: gypsum or lime, smooth finish on lath
0.14 0.10 0.06 0.05 0.04 0.03

Concrete Block, course
0.36 0.44 0.31 0.29 0.39 0.25

Concrete Block, painted
0.10 0.05 0.06 0.07 0.09 0.08

Plaster on brick
0.013 0.015 0.02 0.03 0.04 0.05

Brickwork
0.05 0.04 0.02 0.04 0.05 0.05

Owens-Corning Frescor, painted, 5/8" thick Mounting 7 Drop Ceiling
0.69 0.86 0.68 0.87 0.90 0.81

Drapes cotton 14oz/sq yd
- draped to 7/8 area
0.03 0.12 0.15 0.27 0.37 0.42
- draped to 3/4 area
0.04 0.23 0.40 0.57 0.53 0.40
- draped to 1/2 area
0.07 0.37 0.49 0.81 0.65 0.54

Cotton drapes draped to half area. 15oz/sq yd
0.07 0.37 0.49 0.81 0.65 0.54

Drapes medium velor, 18oz sq yd draped to 1/2 area
0.14 0.35 0.55 0.72 0.70 0.65

Acoustical tile, average 1/2" thick
0.07 0.21 0.66 0.75 0.62 0.49

Acoustical tile, average 3/4" thick
0.09 0.28 0.78 0.84 0.73 0.64

50mm Acoustic Foam
0.08 0.25 0.60 0.90 0.95 0.90

100mm Acoustic Foam
0.20 0.70 0.99 0.99 0.99 0.99

50mm Mineral Wool (Med Density)
0.20 0.45 0.70 0.80 0.80 0.80

Plate glass
0.18 0.06 0.04 0.03 0.02 0.02

6mm glass
0.10 0.06 0.04 0.03 0.02 0.02

Window glass
0.35 0.25 0.18 0.12 0.07 0.04

Breeze block
0.25 0.40 0.60 0.50 0.75 0.50

LF panel absorber
0.28 0.22 0.17 0.09 0.10 0.11

Perforated Helmholz absorber, 4-inch depth, mineral wool damping, 0.79% perforation.
0.40 0.840 0.40 0.160 0.140 0.12

Perforated Helmholz absorber,8-inch depth, mineral wool damping, 0.79% perforation.
0.98 0.88 0.52 0.21 0.16 0.14

Broad-band absorber, 1-inch fibreglass slab at mouth of 7-inch deep cavity
0.67 0.98 0.98 0.93 0.98 0.96

Padded seat (unoccupied)
0.10 0.20 0.25 0.30 0.40 0.30

College students informally dressed seated in tablet arm chairs (per person)
2.5 2.9 5.0 5.2 5.0

Audience seated, depending on spacing and upholstry of seats (per person)
2.5 3.5 4.0 4.5 5.0 4.5

Audience seated, depending on spacing and upholstry of seats (per person)
4.0 5.0 5.5 6.5 7.0 7.0


thought this might be fun to learn about...

cheers
geo