Beat patterns in sound waves
The ear can not distinguishing between two sound waves with a small frequency difference and equal amplitude, the result is that a high frequency and a lower frequency sound is heard. This low frequency sound is known as beating.
The microphone on DrDAQ will enable us to see the beat effect of sound waves.
- Connect each signal generator to one of the loudspeakers and point them into the room placing DrDAQ in the centre, as shown in figure 1.
- Both signal generators should be set to a frequency of approximately 500 Hz.
- PicoScope should now be setup to detect sound (not level) from the speakers, using a timebase of 10 ms/div.
- Switch each of the signal generators on independently, making sure that the amplitude of each soundwave at the microphone is almost identical.
- The equipment is now set up for the experiment.
Figure 1: picture showing the set up of the equipment.
Carrying out the experiment
- Switch on both signal generators.
- Adjust the frequency on one of the signal generators until beating can be heard.
- Capture the waveform seen on PicoScope of the waveform.
- Using the frequency meter in PicoScope make a note of each of the individual frequencies f1 and f2 for the two signal generators by turning each generator off in turn.
- Estimate the beat frequency of the sound wave.
- Estimate the two frequencies of the sound waves from the signal generators.
- What would happen if the amplitudes of the two sound sources were not equal?