Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

• the most efficient way to navigate the Engineering ToolBox!

# Sound Attenuation - Main Duct to Branch Ducts

When main ducts are split into branches the sound power level - Lw - is reduced according the size of the branch, or amount of air to the branch.

The sound attenuation from a main duct to a branched duct can be calculated as

dLN = 10 log (Ab / Am)                                  (1)

where

dLN = sound attenuation (dB)

Ab = branch area (m2, ft2)

Am = main duct area (m2, ft2)

.

The attenuation is indicated in the diagram below:

### Example - Sound Attenuation from Main Duct to Branched Duct

In an example 20% of the air goes to the branch duct and 80% of the air goes further on in the main duct. The branch duct area is 20% of the main duct area before the branch and the main duct area after the branch is 80% of the main duct area before the branch.

The sound attenuation from the main duct to the branch duct can be calculated:

dLN_branch = 10 log ((20%) / (100%))

= 7 dB

The sound attenuation in the main duct can be calculated:

dLN_main_duct = 10 log ((80%) / (100%))

= 1 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 - Duct split to Terminals

Estimating sound attenuation where ducts splits to terminals.

### Sound Attenuation in Duct Elbows

Noise attenuation in duct elbows by reflected sound.

### 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.

### Ventilation Systems - Acoustic Calculation Procedure

Acoustic noise calculation procedure HVAC systems.

## Search Engineering ToolBox

• the most efficient way to navigate the Engineering ToolBox!

## SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

## Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.