Two tuning forks, one of which is adjustable in frequency, demonstrate beats. If the two tuning forks are adjusted to the same frequency and set next to each other, striking one will set up vibrations in the other.
There is a good computer demonstration of beats, which closely represents the tuning fork demonstration above. Two sources are created which play through the room speaker. The wavelength can be changed by dragging and the effects heard. At the same time, the beat waveform or the frequency spectrum can be viewed. This provides a couple different ways to visualize the beats.
The beat bars, tuned to 435 and 440 Hz, produce loud, definite beats. A strong effect is also produced by activating two Rijke Tubes of slightly different lengths. (See Rijke Tubes)
Another good demonstration beats consists of two audio oscillators hooked through a stereo amplifier to speakers. The summed signal is also sent to an oscilloscope so the wave envelope can be seen.