Doppler Horn

Hands On:  

1) Attach a mouthpiece to about 3ft of 3/8″ vinyl hose.

2) Attach a funnel to the other side of the hose.

3) Make sure that there is a lot of space around you – maybe go outside.

4) While blowing in the mouthpiece, take the 2ft closest to the funnel and swing it around your head like you are a cowboy swinging a lasso.  Try to go pretty fast – maybe one or two revolutions around your head per second.


Simple Explanation:  

According to wikipedia, The Doppler effect (or the Doppler shift) is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source.  You can hear this effect in the way that a train sounds as it travels towards or away from you.  As it is moving towards you, the pitch increases.  When it moves away, it decreases.

When you swing the funnel around your head, it creates a doppler effect for the listener.  Because it is moving in a circle, the pitch increases and decreases.  The Hammond B3 Organ used a similar circular doppler effect in its Leslie speakers.

The doppler effect is important to many fields outside of audio – astronomy, medicine, and satellite communication are just some of the fields that use the doppler effect to communicate and measure the world around us.


Further Experimentation:

Try swinging the hose and funnel at different speeds or holding the hose at different lengths.  Do you notice changes in the sound?

Further Learning: