Vibrations of a loudspeaker cone
Practical Activity for 14-16
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
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.
- Increase the frequency slowly from about 10 Hz to a few 100 Hz.
- Watch the resonance of a loudspeaker cone under stroboscopic illumination.
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.