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BBN Empirical Transmission Loss of Double Wall Contruction    1/1

Strutt|Transmission Loss|BBN Double Wall TL calculates the transmission loss of double wall construction using the transmission loss of each wall, the ratio of weights of the wall, the support conditions between the wall and absorption between the walls, using the Bolt Beranek and Newman (BBN) method.

The spreadsheet uses the transmission loss increments for the each compent, these values can be found in the relevant Tables below, and are added to the Transmission Loss values of wall one.

1. For Resiliently Supported Second Wall

a. Second wall weight 1.0 to 0.5 times first wall weight
Separation Octave Band Centre Frequency, Hz
mm inch 63 125 250 500 1k 2k 4k 8k
50 2" 4 6 7 8 10 12 14 16
100 4" 6 7 8 10 12 14 16 18
200 8" 8 10 12 14 16 18 20 22
400 16" 10 12 14 16 18 20 22 24
800 32" 12 14 16 18 20 22 24 26
1600 64" 0.3* to 0.5** times TL of Second Wall Alone
3200 128" 0.7* to 0.9** times TL of Second Wall Alone
* Use these values if there is little or no absorption in the cavity
** Use these values if there is lots of absorption in the cavity

b. Second wall weight 0.4 to 0.1 times first wall weight
Separation Octave Band Centre Frequency, Hz
mm inch 63 125 250 500 1k 2k 4k 8k
50 2" 0 3 4 5 7 9 11 13
100 4" 3 4 5 7 9 11 13 15
200 8" 5 8 10 12 14 16 18 20
400 16" 8 10 12 14 16 18 20 22
800 32" 11 13 15 17 19 21 23 25
1600 64" 0.3* to 0.5** times TL of Second Wall Alone
3200 128" 0.7* to 0.9** times TL of Second Wall Alone
* Use these values if there is little or no absorption in the cavity
** Use these values if there is lots of absorption in the cavity

c. Second wall weight is less than 0.1 times first wall weight
Separation Octave Band Centre Frequency, Hz
mm inch 63 125 250 500 1k 2k 4k 8k
50 2" -2 1 2 3 5 7 9 11
100 4" 1 3 4 6 8 10 12 14
200 8" 4 7 9 11 13 15 17 19
400 16" 7 9 11 13 15 17 19 21
800 32" 10 12 14 16 18 20 22 24
1600 64" 0.3* to 0.5** times TL of Second Wall Alone
3200 128" 0.7* to 0.9** times TL of Second Wall Alone
* Use these values if there is little or no absorption in the cavity
** Use these values if there is lots of absorption in the cavity

2. For Rigidly Supported Second Wall

a. Second wall weight 1.0 to 0.5 times first wall weight
Separation Octave Band Centre Frequency, Hz
mm inch 63 125 250 500 1k 2k 4k 8k
50 2" 4 5 6 6 7 8 9 10
100 4" 5 6 7 8 9 10 11 12
200 8" 6 7 8 10 12 14 16 18
400 16" 8 10 12 14 16 18 20 22
800 32" 12 14 16 18 20 22 24 26
1600 64" 0.3* to 0.5** times TL of Second Wall Alone
3200 128" 0.7* to 0.9** times TL of Second Wall Alone
* Use these values if there is little or no absorption in the cavity
** Use these values if there is lots of absorption in the cavity

b. Second wall weight 0.4 to 0.1 times first wall weight
Separation Octave Band Centre Frequency, Hz
mm inch 63 125 250 500 1k 2k 4k 8k
50 2" 0 2 3 3 4 5 6 7
100 4" 2 3 4 5 6 7 8 9
200 8" 3 5 7 8 10 12 14 16
400 16" 6 8 10 12 14 16 18 20
800 32" 11 13 15 17 19 21 23 25
1600 64" 0.3* to 0.5** times TL of Second Wall Alone
3200 128" 0.7* to 0.9** times TL of Second Wall Alone
* Use these values if there is little or no absorption in the cavity
** Use these values if there is lots of absorption in the cavity

c. Second wall weight is less than 0.1 times first wall weight
Separation Octave Band Centre Frequency, Hz
mm inch 63 125 250 500 1k 2k 4k 8k
50 2" -2 0 1 1 2 3 4 5
100 4" 0 2 3 4 5 6 7 8
200 8" 2 4 6 7 9 11 13 15
400 16" 5 7 9 11 13 15 17 19
800 32" 10 12 14 16 18 20 22 24
1600 64" 0.3* to 0.5** times TL of Second Wall Alone
3200 128" 0.7* to 0.9** times TL of Second Wall Alone
* Use these values if there is little or no absorption in the cavity
** Use these values if there is lots of absorption in the cavity

3. For 50mm-800mm Wall Separation

a. 25mm Thick Acoustic Absorption
Octave Band Centre Frequency, Hz
63 125 250 500 1k 2k 4k 8k
0 0 1 2 3 4 4 4

b. 50mm Thick Acoustic Absorption
Octave Band Centre Frequency, Hz
63 125 250 500 1k 2k 4k 8k
2 2 3 4 5 5 5 5

4. For 1600mm-3200mm Wall Separation

a. Refer to * and ** above