Sound Attenuation in Duct Elbows
Noise attenuation in duct elbows by reflected sound.
Sound power level attenuation in an elbow is caused by sound reflection. It is only in larger ducts and at higher frequencies the attenuation is considerable.
Attenuation in lined and unlined ducts at different sizes and frequencies are indicated in the table below.
| Type | Width B (mm) | Octave band center frequency (Hz) | |||||
|---|---|---|---|---|---|---|---|
| 125 | 250 | 500 | 1000 | 2000 | 4000 | ||
| Ducts Unlined | 150 | 5 | 8 | 4 | |||
| 250 | 5 | 8 | 4 | 3 | |||
| 500 | 8 | 4 | 3 | 3 | |||
| 1000 | 5 | 8 | 4 | 3 | 3 | 3 | |
| Ducts Lined | 150 | 1 | 7 | 16 | 18 | ||
| 250 | 1 | 7 | 16 | 18 | 16 | ||
| 500 | 1 | 5 | 16 | 18 | 16 | 17 | |
| 1000 | 5 | 16 | 18 | 17 | 17 | 18 | |
Example - Sound Attenuation in a Duct Elbow
The sound attenuation in an unlined 500 mm duct elbow at 500 Hz is
8 dB
Related Topics
-
Acoustics
Room acoustics and acoustic properties. decibel A, B and C calculations. Noise Rating (NR) curves. Sound transmission through walls. Calculate sound pressure, sound intensity and sound attenuation. -
Noise and Attenuation
Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems.
Related Documents
-
Lined Sheet-Metal Ducts - Sound Attenuation
Noise attenuation in rectangular straight, lined, sheet metal ducts. -
Sound - Attenuation and Speed vs. Sound Frequency and Air Humidity
The speed and attenuation of sound in moist air varies with sound frequency and air humidity. -
Sound - Attenuation and the Directivity Coefficient
The attenuation in a room depends on the location of the sound source and the receiver - and the room constant. -
Sound Attenuation - Duct split to Terminals
Estimating sound attenuation where ducts splits to terminals. -
Sound Attenuation - Main Duct to Branch Ducts
Sound attenuation from main ducts to branch ducts. -
Sound Attenuation in Ducts due to End Reflection
Low frequency noise transferred from main duct to end terminals is reflected back to main duct. -
Sound Transmission through Duct Walls
Sound transmission from ducts to surrounding rooms. -
Sound Transmission through Flanking Paths
Sound transmitted through duct walls, floors and ceilings. -
Unlined Sheet-Metal Ducts - Sound Attenuation
Noise attenuation in unlined sheet-metal ducts.
