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.

Noise generated in Air Ducts

Sponsored Links

Air flow in ducts generates noise. The noise in the duct is determined by

  • air velocity
  • duct size (cross sectional area)

Generated noise can be calculated with the empirical equation

LN = 10 + 50 log (v) + 10 log (A)                                                       (1)


LN = sound power level in the duct (dB)

v = air velocity (m/s)

A = air duct cross sectional area (m2)

The equation modified for imperial units

LN = 10 + 50 log (vi / 197) + 10 log (Ai / 1550)                                                      (1b)


vi = air velocity (ft/min)

Ai = cross sectional area (in2)


Example - Generated Noise in Duct by Air Flow

The cross section area of a 200 mm duct can be calculated as

A = π ((0.2 m) / 2)2)

   = 0.0314  m2

The noise generated in the duct with an air flow velocity 10 m/s can be calculated as

 LN = 10 + 50 log (10 m/s) + 10 log (0.0314 m2)

    = 45 db

The noise generated in the same 200 mm circular duct as above with air flow velocity 20 m/s can be calculated as

 LN = 10 + 50 log (20 m/s) + 10 log (π ((0.2 m) / 2)2)

    = 60 db

Note! - due to the noise generated by fans - noise generated inside ducts by air flow can in general be neglected.

Sponsored Links

Related Topics


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


Logarithmic unit used to describe ratios of signal levels - like power or intensity - to a reference level.

Ducts Sizing - the Velocity Reduction Method

The velocity reduction method can be used when sizing air ducts.

Ductwork - Seal Classes

Ductwork air leakage classes.

Fans - Noise Power Generation

The sound generated by a fan depends on the motor power, the volume capacity, the static pressure increase and the discharged volume.

Noise Attenuation in Rotary Heat Exchanges

Sound attenuation vs. frequency in rotating heat exchangers.

Signals - Adding Decibels

The logarithmic decibel scale is convenient when adding signal values like sound power, pressure and others from two or more sources.

Velocity Classification of Ventilation Ducts

Recommended air velocities in ventilation ducts

Sponsored Links

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!


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.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.