Education and Manpower Bureau
Using Datalogger in Teaching of Physics


Sound Beats

Experiment Profile:

1. Introduction

When two sound waves with different but close frequencies interfere with each other. What is heard is a sound whose frequency is the average of the two original frequencies. This sound varies in intensity and the variations in intensity have a frequency that is equal to the difference between the two original frequencies.

If the original waves are:

Where f1, f2 are the frequencies, than the composite wave will be of the form:

in this experiment we explore the form of the composite wave by viewing the readings of a microphone and by looking at the Fourier transform of these readings.

2. Equipment List
Data logger interface connected with PC
Two tuning forks mounted on sounding boxes (frequencies: 440 Hz, 435 Hz)
A rubber hammer to sound the forks
Sound sensor



1. Connect up the circuit as shown in Figure 1.

2. Connect the sound sensor to a socket on the interface.

3. Hit one of the tuning forks with the rubber hammer. Wait a few seconds for the hight pitched harmonies to subside.
4. While the fork is still sounding, start the software to collect data.

5. Save the results.

6. Repeat step 1 to 3 with the other tuning fork. Remember to save the collected data under a different file name.

7. Repeat step 1 to 3 while sounding both forks simultaneously. Save the result under a new file name.


1. Describe what you hear while sounding both tuning forks simultaneously?

2. Please describe the 3 graph generate and give explanation to your result.

3. If we replace one of the tuning fork to a higher frequency (for example: 480Hz), what can you hear?

4. Is there any difference in the graph generated?

Video Download:

We are particularly grateful to SKH Kei Hau Secondary School for their help in production of this video.
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