Noise Reduction Silencers
Reference data and engineering information about noise reduction silencers for acoustics applications.
noisereductionsilencers
Overview
Engineering reference data for Noise Reduction Silencers in acoustics.
Key Formulas
Speed of Sound
Speed of sound in an ideal gas.
Sound Level
Decibel level.
Wavelength
Wavelength = speed / frequency.
Variables
| Symbol | Description | Unit |
|---|---|---|
| Speed of sound | m/s | |
| Sound level | dB | |
| Wavelength | m | |
| Frequency | Hz |
Silencer Performance Data
7 rows
Diameter(inches) | Length(inches) | 125 Hz(dB) | 250 Hz(dB) | 500 Hz(dB) | 1000 Hz(dB) | 2000 Hz(dB) | 4000 Hz(dB) | 8000 Hz(dB) |
|---|---|---|---|---|---|---|---|---|
| 4 | 24 | 8 | 14 | 26 | 34 | 41 | 45 | 25 |
| 5 | 24 | 6 | 12 | 22 | 28 | 37 | 38 | 22 |
| 6 | 24 | 5 | 10 | 18 | 23 | 33 | 30 | 19 |
| 8 | 24 | 4 | 9 | 17 | 22 | 29 | 25 | 18 |
| 10 | 36 | 6 | 11 | 21 | 27 | 39 | 25 | 19 |
| 12 | 36 | 5 | 9 | 18 | 23 | 32 | 20 | 18 |
| 16 | 36 | 5 | 8 | 11 | 23 | 19 | 17 | 15 |
Source: engineeringtoolbox.com
Silencer Classifications
Absorptive (Dissipative) Silencers
- Use sound-absorbing materials (fibrous linings) to attenuate sound.
- Energy is transformed to heat via fiber motion.
- Baffle thickness is selected based on the predominant noise frequency.
- Common types: lined ducts, packaged attenuators, acoustic louvers, lined plenum chambers.
- Widely used in HVAC systems.
Reflective (Reactive) Silencers
- Reflect sound waves back toward the source using tuned cavities or membranes.
- Operate on principles of lambda/4- and Helmholtz-resonators.
- Excel at attenuating low-frequency, pure-tone noise.
- Non-fibrous, cleanable, with low pressure drop.
- Best for fixed-speed machinery; rarely used in HVAC.
Diffuser (Depressive) Silencers
- Use perforated "pepper pots" to slow flow velocity and reduce low-frequency noise generation.
- Divide total pressure drop across multiple stages (e.g., nozzle, valve, diffuser).
- Primarily used for nozzles, control valves, and jet engines.
Active Silencers
- Employ electro-acoustic means (microphones, speakers, electronics) to generate an anti-phase sound field that cancels noise.
- Effective for steady, low-frequency noise (< 300 Hz) from sources like fans and engines.
- Not suitable for broadband noise reduction.