Sound Wave Interference Notes

Transducer Setup and Sound Wave Interference

• Two transducers are set up in front of schlieren optics, angled towards each other.
• The goal is to observe the interference patterns of sound waves emanating from each transducer.

Observation of Individual Sound Waves

• When one transducer is activated, sound waves are visible.
• These sound waves are pressure waves moving through the air at the speed of sound.
  • They appear frozen because the light is strobing (turning on and off) at the same rate as the sound wave production: $28,000$ times per second.

Sound Wave Interference

• With both transducers on, an interference pattern is observed where the waves intersect.
• Constructive Interference:
  • Occurs where wave crests meet.
  • These points appear brighter due to the additive effect of the waves.

Observation of Progressing Waves and Interference

• When the strobing frequency is lowered, the waves appear to progress forward.
• Points of constructive interference move vertically upward.
  • Along the vertical line bisecting the transducers, the distance traveled by waves from each transducer is equal, resulting in constant constructive interference.
• Decreasing the strobing frequency further increases the apparent speed of the waves.

Continuous Illumination and Constructive Interference Zones

• With continuous illumination, individual traveling waves are no longer visible due to their high speed.
• Instead, bands or zones of light are observed.
• These bands represent regions of continuous constructive interference.
  • The "dots" that appeared to move upward under strobing are now seen as stable zones where the crests of the waves continuously meet.
  • These zones are visible because the constructive interference is continuous, not sporadic.