Sound Transmission through Duct Walls
Sound transmission from ducts to surrounding rooms.
Sound or noise transmitted from the inside of a duct to the surrounding room can be expressed as:
Lp = LN - TL - 10 log (A F / 4 Ad) (1)
where
Lp = sound pressure in room (dB)
LN = sound power level in the duct (dB)
TL = transmission loss through duct wall (dB)
A = room absorption (m2 sabine)
F = cross section area of duct (m2)
Ad = surface area of duct (m2)
Typical sound transmission loss through duct walls are indicated in the table below:
Duct sheet thickness (mm) | Frequency (Hz) | |||
---|---|---|---|---|
125 | 250 | 500 | 1000 | |
1.25 | 17 | 22 | 25 | 29 |
1.0 | 15 | 20 | 23 | 27 |
0.75 | 14 | 19 | 22 | 26 |
0.65 | 12 | 17 | 20 | 24 |
The acoustic performance of round and oval ducts is superior to rectangular ducts since their curved surfaces allow less breakout noise. Low-frequency sound is better contained in round ducts.
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 - 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 Duct Elbows
Noise attenuation in duct elbows by reflected sound. -
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 Flanking Paths
Sound transmitted through duct walls, floors and ceilings. -
Unlined Sheet-Metal Ducts - Sound Attenuation
Noise attenuation in unlined sheet-metal ducts. -
Ventilation Systems - Classification of Noise Reduction Silencers
Noise in a ventilation system can be reduced by reactive, diffuser type, active and/or dissipative silencers.