Basic Documentation

Chapter 4–HVAC Sound Attenuation
Diamete
r
63 125 250 500 1,000 2,000 4,000 8,000
Inches Hz Hz Hz Hz Hz Hz Hz Hz
12
0.23 0.46 0.81 1.45 2.18 1.91 1.48 1.05
14
0.19 0.42 0.77 1.43 2.14 1.79 1.34 1.00
16
0.16 0.38 0.73 1.40 2.08 1.67 1.21 0.95
18
0.13 0.35 0.69 1.37 2.01 1.56 1.10 0.90
20
0.11 0.31 0.65 1.34 1.92 1.45 1.00 0.87
22
0.08 0.28 0.61 1.31 1.82 1.34 0.92 0.83
24
0.07 0.25 0.57 1.28 1.71 1.24 0.85 0.80
26
0.05 0.22 0.53 1.24 1.59 1.14 0.79 0.77
28
0.03 0.19 0.49 1.20 1.46 1.04 0.74 0.74
30
0.02 0.16 0.45 1.16 1.33 0.95 0.69 0.71
32
0.01 0.14 0.42 1.12 1.20 0.87 0.66 0.69
34
0 0.11 0.38 1.07 1.07 0.79 0.63 0.66
36
0 0.08 0.35 1.02 0.93 0.71 0.60 0.64
38
0 0.06 0.31 0.96 0.80 0.64 0.58 0.61
40
0 0.03 0.28 0.91 0.68 0.57 0.55 0.58
42
0 0.01 0.25 0.84 0.56 0.50 0.53 0.55
44
0 0 0.23 0.78 0.45 0.44 0.51 0.52
46
0 0 0.20 0.71 0.35 0.39 0.48 0.48
48
0 0 0.18 0.63 0.26 0.34 0.45 0.44
50
0 0 0.15 0.55 0.19 0.29 0.41 0.40
52
0 0 0.14 0.46 0.13 0.25 0.37 0.34
54
0 0 0.12 0.37 0.09 0.22 0.31 0.29
56
0 0 0.10 0.28 0.08 0.18 0.25 0.22
58
0 0 0.09 0.17 0.08 0.16 0.18 0.15
60
0 0 0.08 0.06 0.10 0.14 0.09 0.07
Duct Elbows
Duct elbows are quite effective at attenuating sound in the mid frequency levels. The most
effective attenuation is in rectangular elbows, which are lined elbows and do not have turning
vanes. The minimum attenuation occurs in unlined round elbows. More data has been
derived for rectangular elbows. Round elbows that are lined present a very complex scenario
and, for that reason, are not discussed here.
58 Siemens Building Technologies, Inc.