Wave Motion and Sound

Spring

• Aluminum spring rail (with speaker w/ hook mounted on one end and pully mounted on the other)
  • Spring (2-inch)
  • Mass pan w/ assortment of small masses (maximum total mass = XX)
  • String (to attach mass pan to spring)
• Pasco low frequency function generator
• Meter stick

Attach one end of the spring to the speaker and the other end to the string attached to the mass pan. With full mass, spring should extend nearly the full length of the rail.

Test the setup by attempting to find resonance around 10 Hz. (Fundamental frequency is near 5 Hz, but it easier to see the $n = 2$ or $n = 3$ cases where there are nodes along the spring).

String

• Optical Rail
  • “String” kit (post with speaker holder and speaker, heavy string, post with pulley, heavy mass pan)
  • Two post holders
  • BK function generator (un-modified)
  • Meter stick

Setup tips:

• The speaker needs to close to the top of the post, but make sure the string is not touching the edges of the speaker when taut.
• Make sure the string is close to level with the posts at even heights. (It is harder to see resonance if the two ends are not level.)
• The speaker should be delivering as close to a pure vertical motion as possible. (Avoid driving at an angle.)
• Check to make sure the speaker cone is not ripped or damaged.

Test the setup by looking for resonance near 50 Hz (near where $n = 2$) or 100 Hz ($n = 4$). This gives you a few nodes to look for.

Sound tube

• Optical rail
  • Four post holders
  • Two tube holders
  • Tube with plunger
  • Sound level meter (on post)
  • Post with short speaker holder
  • Speaker (preferably without hook)
• BK function generator (unmodified preferred, but modified OK).
• Oscilloscope
• Two long BNC cables
• BNC to double-banana adapter
• Meter stick

Setup tips:

• The speaker should be close to (but below) the sound level meter.
• Place the tube height to be about the midpoint between speaker and sound level meter.
• Set function generator to sine wave and adjust the amplitude down to lowest setting (either fully counter-clockwise, or fully-counter-clockwise AND pulled out to attenuate further). There is no need for the sound to be loud.
• Make sure all other function generator buttons are turned fully counter-clockwise (zero or off).

Test the setup by looking for resonance around 5 kHz. (This is a good middle range where the speaker movement is clean and the cycling between standing waves can be audibly heard as the plunger moves). Adjust positioning so that difference between constructive and destructive interference is large and clear.

• Earplugs (optional for those who are bothered by the noise)
• Balance
• Extra parts
  • Function generator
  • Oscilloscope
  • Speaker(s)
  • BNC to double-banana adapters
  • Springs and mass pans