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BBN Empirical Transmission Loss of Double Wall Contruction
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Strutt|Building Acoustics|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 strutt 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
Comments or suggestions to
strutt@arup.com