Basic Documentation

Duct Attenuation
Table 21. Two-Inch Thick Fiberglass Lined Round Duct Attenuation Per Foot of Length.
Diamete
r
63 125 250 500 1,000 2,000 4,000 8,000
Inches Hz Hz Hz Hz Hz Hz Hz Hz
6
0.56 0.80 1.37 2.25 2.17 2.31 2.04 1.26
8
0.51 0.75 1.33 2.23 2.19 2.17 1.83 1.18
10
0.46 0.71 1.29 2.20 2.20 2.04 1.64 1.12
12
0.42 0.67 1.25 2.18 2.18 1.91 1.48 1.05
14
0.38 0.63 1.21 2.15 2.14 1.79 1.34 1.00
16
0.35 0.59 1.17 2.12 2.08 1.67 1.21 0.95
18
0.32 0.56 1.13 2.10 2.01 1.56 1.10 0.90
20
0.29 0.52 1.09 2.07 1.92 1.45 1.00 0.87
22
0.27 0.49 1.05 2.03 1.82 1.34 0.92 0.83
24
0.25 0.46 1.01 2.00 1.71 1.24 0.85 0.80
26
0.24 0.43 0.97 1.96 1.59 1.14 0.79 0.77
28
0.22 0.40 0.93 1.93 1.46 1.04 0.74 0.74
30
0.21 0.37 0.90 1.88 1.33 0.95 0.69 0.71
32
0.20 0.34 0.86 1.84 1.20 0.87 0.66 0.69
34
0.19 0.32 0.82 1.79 1.07 0.79 0.63 0.66
36
0.18 0.29 0.79 1.74 0.93 0.71 0.60 0.64
38
0.17 0.27 0.76 1.69 0.80 0.64 0.58 0.61
40
0.16 0.24 0.73 1.63 0.68 0.57 0.55 0.58
42
0.15 0.22 0.70 1.57 0.56 0.50 0.53 0.55
44
0.13 0.20 0.67 1.50 0.45 0.44 0.51 0.52
46
0.12 0.17 0.64 1.43 0.35 0.39 0.48 0.48
48
0.11 0.15 0.62 1.36 0.26 0.34 0.45 0.44
50
0.09 0.12 0.60 1.28 0.19 0.29 0.41 0.40
52
0.07 0.10 0.58 1.19 0.13 0.25 0.37 0.34
54
0.05 0.08 0.56 1.10 0.09 0.22 0.31 0.29
56
0.02 0.05 0.55 1.00 0.08 0.18 0.25 0.22
58
0 0.03 0.53 0.90 0.08 0.16 0.18 0.15
60
0 0 0.53 0.79 0.10 0.14 0.09 0.07
To approximate the attenuation provided by either a rectangular or round elbow, first
calculate the Frequency Width (FW) factor for the elbow at each octave band as follows:
FW = (Frequency x Width) ÷ 1,000
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