The type of vibration generator pictured above is to be used in conjunction with a signal generator to produce varying vibrating frequencies which in turn can be used to create waves along a piece of string.
The signal generator supplies a small electric current at a specific frequency which the vibrator converts into movement in exactly the same way as a loudspeaker works. Inside the unit is a coil of wire, magnet a diaphragm which converts this signal into vertical movement of the diaphragm. This is connected to a pin which sticks out of the top of the unit to which string can be attached.
The vibrator should be attached securely to a clamp and stand so it cannot move and a length of string attached to the end of the pin. The other end of the string can be fixed to a clamp or attached to masses and strung over a clamp pulley fixed to an edge of the demonstration bench.
When a specific frequency is applied to the vibrator, the string should start to display a waveform along its length. As you increase the frequency, more and more loops in the string should become visible. The waveform displayed can be compared to that displayed on an oscilloscope when connected to a signal generator.
Using this equipment the speed of the displayed wave can be calculated using the known wavelength and frequency. The relationship between frequency, wavelength and tension in the string could also be observed if you use the masses and clamp pulley.
A stroboscope or strobe wheel can be used to make the waveform stand out better