Handbook of air conditioning and refrigeration / Shan K

19.22 CHAPTER NINETEEN
TABLE 19.11 TL in for Round Ducts at Various Octave Bands, dB
TL in, dB
Diameter, Length,
Octave band center frequency, Hz
in. ft Gauge 63 125 250 500 1000 2000 4000
8 15 26 �17
Long seam ducts
(31) 39 42 41 32 31
14 15 24 �27 43 43 31 31 28 22
22 15 22 �28 40 30 30 30 24 22
32 15 22 (35) 36 23 23 21 19 35
Spiral-wound ducts
8 10 26 �20 �42 �59 �62 53 43 26
14 10 26 �20 �36 44 28 31 32 22
26 10 24 �27 38 20 23 22 19 33
26 10 16 �30 �41 30 29 29 25 38
32 10 22 �27 32 25 22 23 21 37
Note: In cases where background sound swamped the sound radiated from the duct walls, a lower limit on TL in is indicated
by a � sign. Parentheses indicate measurements in which background sound has produced a greater uncertainty than usual.
Source: ASHRAE Handbook 1995, HVAC Applications. Reprinted by permission.
TABLE 19.12 TL in for Rectangular Ducts at Various Octave Bands, dB
Duct size Octave band center frequency, Hz
in. Gauge 63 125 250 500 1000 2000 4000 8000
12 � 12 24 16 16 16 25 30 33 38 42
12 � 24 24 15 15 17 25 28 32 38 42
12 � 48 22 14 14 22 25 28 34 40 42
24 � 24 22 13 13 21 26 29 34 40 42
24 � 48 20 12 15 23 26 28 36 42 42
48 � 48 18 10 19 24 27 32 38 42 42
48 � 96 18 11 19 22 26 32 38 42 42
The data are tests on 20-ft-long ducts, but the TL values are for ducts of the cross section shown regardless of length.
Source: Adapted with permission from ASHRAE Handbook 1991, HVAC Applications.
TABLE 19.13 TL in for Flat Oval Ducts at Various Octave Bands, dB
TL in, dB
Duct size
Octave band center frequency, Hz
in.� in. Gauge 63 125 250 500 1000 2000 4000
12 � 6 24 18 18 22 31 40 — —
24 � 6 24 17 17 18 30 33 — —
24 � 12 24 15 16 25 34 — — —
48 � 12 22 14 14 26 29 — — —
48 � 24 22 12 21 30 — — — —
96 � 24 20 11 22 25 — — — —
96 � 48 18 19 28 — — — — —
Note: The data are for duct lengths of 20 ft, but the values may be used for the cross section
shown regardless of length.
Source: ASHRAE Handbook 1995, HVAC Applications. Reprinted by permission.