Materials:

• Oscilloscope
• Function Generator (2)
• Speakers (2)
• Tuning Forks (same frequency) (2)
• Microphone
• Connection Leads

Demo:

Two versions are available:

1. With tuning forks of the same frequency with resonant boxes (shown to the left). Place them next to each other and tune them to a few Hz apart. When the forks are struck with a rubber hammer, and with the microphone near the box openings, the auditorium will hear and see the beats.
2. Two functional generators are set a few Hz apart and power the two speakers (shown to the right). Put the microphone between the speakers to show beat patterns on the oscilloscope screen.

Explanation:

Figure 1 – Two waves of frequencies a few Hz apart construcively and destructively interfere to create a beat pattern. C.I. and D.I. stands for constructive and destructive interference, respectively. Used from lesson on interference and beats at physicsclassroom.com

When two tones of frequencies a few Hz apart are generated, the two sound waves will interfere constructively and destructively with a frequency equal to the difference in frequencies between the two tones, as shown in Figure 1

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