Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Vibrations of a loudspeaker cone

Demonstration

This experiment shows how AC oscillations from the generator become sound oscillations at the loudspeaker.

Apparatus and materials

  • signal generator
  • large loudspeaker
  • xenon stroboscope
  • 4 mm leads
  • semolina or rice, a small amount

Health & Safety and Technical notes


Read our standard health & safety guidance

Clamp the loudspeaker so that it faces upwards. Connect the low impedance output of the signal generator to the loudspeaker. Place a few grains of semolina or rice in the cone so that resonances show up clearly, as the generator frequency changes.

Safety note: Using the xenon stroboscope, teachers should be aware that frequencies around 7 Hz have been known to cause epileptic fits in certain people. Ask your students if any know that they are susceptible to this response.  

Procedure


a Increase the frequency slowly from about 10 Hz to a few 100 Hz.

b Watch the resonance of a loudspeaker cone under stroboscopic illumination.

Teaching notes


1 The standing waves should be viewed stroboscopically, as well as by eye, to give students a clear understanding of their nature.

This experiment has yet to undergo a health and safety check.

 

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