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

# Sound - Doppler Effect

## The doppler effect is the change in sound frequency due to the relative motion between a source and a listener.

The change in frequency of sound due to relative motion between a source and a listener is called the Doppler Effect.

The observed sound frequency for a listener can be expressed as

fr = fs (c + vr) / (c + vs)                                 (1)

where

fr = frequency observed by the receiver (1/s, Hz)

fs = frequency emitted from the source (1/s, Hz)

c = speed of sound (m/s)

vr = velocity of the receiver relative to the medium - positive if the receiver is moving towards the source (m/s)

vs = velocity of the source relative to the medium - positive if the source is moving away from the receiver (m/s)

### Example - A Train passing a Bell

A train with speed 200 km/h (55.6 m/s) passes a bell with sound frequency 1000 Hz. With an air temperature of 20 oC the speed of sound is 343 m/s.

The frequency observed by a passenger in the train before passing the bell can be calculated as

fr = (1000 Hz) ((343 m/s) + (55.6 m/s)) / ((343 m/s) + (0 m/s))

= 1162 Hz

The frequency observed by the passenger in the train after passing the bell can be calculated as

fr = (1000 Hz) ((343 m/s) + (- 55.6 m/s)) / ((343 m/s) + (0 m/s))

= 838 Hz

### Doppler Effect Calculator

Calculate the observed frequency with the calculator below:

fs - frequency emitted from the source (Hz) -

c - speed of sound (m/s)

vr - velocity of the receiver relative to the medium (m/s) - m/s vs. km/h vs. mph

vs - velocity of the source relative to the medium (m/s)

## Related Topics

• ### Acoustics

Room acoustics and acoustic properties, decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation.

## Related Documents

• ### Air - Speed of Sound vs. Temperature

Speed of sound in air at standard atmospheric pressure with temperatures ranging -40 to 1000oC (-40 to 1500oF) - Imperial and SI Units.
• ### Decibel A, B and C

Sound pressure filters that compensates for the hearing sensed by the human ear.
• ### Fluid Flowmeters - Comparing Types

An introduction to the different types of fluid flowmeters - Orifices, Venturies, Nozzles, Rotameters, Pitot Tubes, Calorimetrics, Turbine, Vortex, Electromagnetic, Doppler, Ultrasonic, Thermal, Coriolis.
• ### Notes, Octaves and Frequencies

Frequencies vs. notes and octaves.
• ### Sound Power

Sound power from sources like fans, jet engines, cars, humans and more.
• ### Speed of Sound - Online Calculator

A free online speed of sound calculator.
• ### Ultrasonic Doppler and Time of Flight Velocity and Volume Flow Meters

An basic introduction to the ultrasonic Doppler and Time of Flight Flow Meters.

## 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 older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

We don't collect information from our users. More about

## Citation

• The Engineering ToolBox (2012). Sound - Doppler Effect. [online] Available at: https://www.engineeringtoolbox.com/doppler-effect-d_1839.html [Accessed Day Month Year].

Modify the access date according your visit.

close

9.19.12