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 ÷ 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) |
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|---|---|---|---|---|
| 12 (305) U-Unite Size in (mm) | VRS/2 Silencer Type | - L x Length in (mm) | M x N Cross Section in (mm) |  |
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