Handbook of air conditioning and refrigeration / Shan K

19.8 CHAPTER NINETEEN
TABLE 19.3 Sound Attenuation (Insertion Loss) for Straight Lined Sheet-Metal Rectangular Ducts, Lining
Thickness 1 in.
Octave and center frequency, Hz
Internal
cross-sectional
63 125 250 500 1000 2000 4000 8000
dimensions, in. Attenuation, dB/ft
8 � 8 0.77 0.90 1.29 2.57 6.23 5.94 3.49 2.42
8 � 18 0.60 0.67 1.04 2.22 5.10 4.72 3.06 2.26
12 � 12 0.56 0.60 0.96 2.09 4.70 4.29 2.90 2.20
12 � 24 0.50 0.48 0.79 1.81 3.85 3.41 2.54 2.06
18 � 18 0.40 0.43 0.74 1.70 3.54 3.10 2.41 2.00
18 � 36 0.30 0.32 0.59 1.47 2.90 2.46 2.11 1.87
24 � 24 0.30 0.32 0.59 1.47 2.90 2.46 2.11 1.87
24 � 48 0.23 0.24 0.47 1.27 2.37 1.95 1.85 1.76
36 � 36 0.21 0.21 0.43 1.20 2.19 1.78 1.75 1.71
36 � 72 0.16 0.16 0.34 1.03 1.79 1.41 1.54 1.60
48 � 48 0.16 0.16 0.34 1.03 1.79 1.41 1.54 1.60
48 � 72 0.14 0.13 0.29 0.94 1.58 1.22 1.42 1.54
1. Based on measurements of surface-coated duct liners of 1.5 to 3 lb/ft 3 density. For the specific materials tested, liner density
had a minor effect over the nominal range of 1.5 to 3 lb/ft 3 .
2. Add natural attenuation (Table 19.1) to obtain total attenuation.
Source: Abridged with permission from ASHRAE Handbook 1995, HVAC Applications.
TABLE 19.4 Lined Flexible Duct Insertion Loss
Insertion loss dB
Diameter, Length,
Octave band center frequency, Hz
in. ft 63 125 250 500 1000 2000 4000
8 12 8 11 21 33 37 37 24
9 6 8 16 25 28 28 18
6 4 6 11 17 19 19 12
3 2 3 5 8 9 9 6
9 12 8 11 22 33 37 36 22
9 6 8 17 25 28 27 17
6 4 6 11 17 19 18 11
3 2 3 6 8 9 9 6
10 12 8 10 22 32 36 34 21
9 6 8 17 24 27 26 16
6 4 5 11 16 18 17 11
3 2 3 6 8 9 9 5
12 12 7 9 20 30 34 31 18
9 5 7 15 23 26 23 14
6 3 5 10 15 17 16 9
3 2 2 5 8 9 8 5
14 12 5 7 16 27 31 27 14
9 4 5 12 20 23 20 11
6 3 4 8 14 16 14 7
3 1 2 4 7 8 7 4
Source: ASHRAE Handbook 1995, HVAC Applications. Reprinted with permission.