KINETICS®

Guidelines to Selecting a Rectangular Silencer

Step 1 - Determining System Parameters

The following information is needed to determine silencer Insertion Loss (IL) and Pressure Drop (PD) performance:

  • Silencer IL requirements
  • Unit size
  • Forward (supply) or reverse (return) airflow direction
  • Maximum allowable silencer PD
  • Face velocity
  • Length, width and height restrictions

1.1

The IL requirements, quoted for octave bands 1 through 8, may be determined by:

  • Comparison to an existing specification
  • Duct system analysis using Kinetics web-based design program
  • Application-dependent requirements, such as elimination of low frequency or tonal noise

Definition of Octave Bands

Octave Band Number 1 2 3 4 5 6 7 8
Center Frequency (Hz) 63 125 250 500 1000 2000 4000 8000

1.2

To identify unit sizes available for common duct sizes see Table 1 - Common Unit Sizes (below). If a duct dimension is an odd number, round up to the next even number.

1.3

IL data for airflow velocities available on request. Forward and reverse flow are defined as follows:

  • Forward Flow: airflow in the silencer is in the same direction as the noise propagation
  • Reverse Flow: airflow in the silencer is in the opposite direction to the noise propagation

Table 1 - Common Unit Sizes

M or N in (mm) Available Unit Sizes
10 (254) 10 (254), 20 (508)
12 (305) 12 (305), 24 (610)
14 (356) 14 (356), 28 (711)
16 (406) 16 (406)
18 (457) 18 (457)
20 (508) 10 (254), 20 (508)
22 (559) 11 (279), 22 (559)
24 (610) 12 (305), 24 (610)
26 (660) 13 (330), 26 (660)
28 (711) 14 (356), 28 (711)
30 (762) 10 (254), 15 (381), 30 (762)
32 (813) 10.7 (272), 16 (406)
34 (864) 11.3 (287), 17 (432)
36 (914) 12 (305), 18 (457)
38 (965) 12.7 (323) 19 (483)
40 (1016) 10 (254), 13.3 (338), 20 (508)
42 (1067) 10.5 (267), 14 (356), 21 (533)
44 (1118) 11 (279), 14.7 (373), 22 (559)
46 (1168) 11.5 (292), 15.3 (389), 23 (584)
48* (1219) 12 (305), 16 (406), 24 (610)

*Silencers with M or N greater than 48 in. (1219 mm) will be made in multiple pieces - see Selection of Large Silencers.

1.4

The allowable PD may be determined by:

  • Comparison to an existing specification
  • Through consultation with the mechanical engineer

1.5

The face velocity is calculated using the following formula:

FACE VELOCITY= AIRFLOW RATE รท DUCT CROSS-SECTIONAL AREA

Step 2 - Select IL Performance

Contact Kinetics Noise Control for more information on selecting IL performance

Step 3 - Select PD Performance

Contact Kinetics Noise Control for more information on selecting PD performance

Sample Silencer Model vs. Contractor

Typical Silencer Model Designation
12VSR/2-L x M x N (305VRS/2 - L x M N)
12 (305) U-Unite Size in (mm) VRS/2 Silencer Type - L x Length in (mm) M x N Cross Section in (mm)
  • Silencers with M and N under 48 in. (1219mm) will be made in one piece
  • M is always perpendicular to the plane of the baffle
  • Baffles shown here are vertical
  • Baffles may be either vertical or horizontal

Mechanical Systems

Vibration Isolation Seismic & Wind Noise Control
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