Introduction to Sound Waves

Timothy Cameron
Mechanical Engineering Department
GMI Engineering & Management Institute
Flint, MI, 48504

This laboratory whets the students' appetite for acoustics by exposing them to a sampling of acoustic phenomena and applications. Students informally test the frequency limits of their own hearing, measure the speed of sound, perform a simple sonar rangefinding exercise, and observe the cancellation of sound. Equipment is limited to function generators and oscilloscopes (which students have used in previous laboratory courses), a loudspeaker, and a microphone. Emphasis is placed on discovering some of the more basic aspects of sound, including the relationships between frequency, speed, and wavelength, the behavior of a single frequency signal, and the concept of sound cancellation by another sound.

What Range of Frequencies Can You Hear?

(Must have separate data for each group member)

Equipment required:

  1. HP33120A Function/Arbitrary Waveform Generator
  2. One speaker mounted in a fixture
  3. One cable

Directions:

Hook up speaker to the function generator. Turn on the function generator and set it to a sine wave with a frequency of10Hz and Amplitude 20 Vpp. Slowly increase the frequency and record the frequency at which you start hearing sound and the frequency at which you can no longer hear a signal because it is too high.

Measure the Speed of Sound

Equipment required:

  1. HP33120A Function/Arbitrary Waveform Generator
  2. HP54600B Oscilloscope
  3. One speaker mounted in a fixture
  4. Microphone
  5. Yardstick

Directions:

Connect speaker and oscilloscope to function generator. Connect microphone to the 1X and the function generator to the 2Y on the oscilloscope. Generate a pure tone, f, on the function generator. Position the microphone so its signal is in phase w/ the function generator's signal. Note the position of the mic. Move the mic until its signal moves one full period later/earlier. Note new position. Difference in position = ????

Noise Cancellation

Equipment required:

  1. HP33120A Function/Arbitrary Waveform Generator
  2. Two speakers mounted in a fixture
  3. HP54600B Oscilloscope
  4. Microphone

Directions:

Measure the SPEED OF SOUND first. Hook up the two speakers to the function generator along with the oscilloscope. Hook up the microphone to the oscilloscope. Generate pure tone, f, on the function generator. Find the distance between the speakers required for their signal to cancel. What proportion of the wavelength, , is this?

Distance Measurement with Sound Pulse

Equipment required:

  1. HP33120A Function/Arbitrary Waveform Generator
  2. One speaker mounted in a fixture
  3. A microphone
  4. An HP54600B Oscilloscope
  5. Reflecting surface

Directions:

Hook up the function generator to channel 2 and the microphone to channel 1 of the oscilloscope. Set the source to channel 2, trigger to normal, 200 mV per division, 200us per division, and time reference left under the main delay menu. Put the microphone in front of the speaker facing the reflective surface so that it shows the output from the speaker and the returned sound from the reflecting surface. Place the reflecting surface facing the microphone tip. Find the distance using EQUATION?????