A number of audio generators (with speakers) are available for
There is a high precision generator with a
digital readout of the frequency that can be used to demonstrate resonance,
beats (if two are used), etc. But it only produces sine waves.
The Pasco dual wave generator will produce one or two waves with a
variety of shapes (sine, square, pulse, triangle). The frequency is
not as well calibrated, but the variety of shapes is useful. For example,
using the clicks, you can explore the low frequency boundary between
separately audible clicks and a buzz with a discernable pitch.
however, that the response of the average speaker is such that a
triangle wave on the generator will not in general produce a
triangle audio wave!
With just one magnet, a good introductory demonstration for magnetism.