Sound Wave Physics: X-Axis vs. Trough

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Discussion Overview

The discussion revolves around the nature of sound waves as represented on an oscilloscope, specifically addressing where silence occurs in relation to the x-axis and the trough of a sine wave. The conversation includes aspects of auditory perception, sound measurement, and the behavior of sound waves in different contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether silence occurs on the x-axis or at the trough of a sine wave when listening to sound.
  • Another participant asserts that sound is dependent on amplitude, suggesting that it is zero on the x-axis.
  • A different participant emphasizes that hearing involves the brain and not just the physical properties of sound waves, noting that loudness remains constant across a frequency range.
  • This participant also discusses the behavior of sound waves in relation to loudspeakers, mentioning that the change in air pressure is zero when the speaker cone is at its midpoint, while air velocity is zero at maximum and minimum displacements.
  • Another participant argues that sound would not be silent anywhere on the wave, stating that silence would only occur with a flat line, and points out that the highest rate of change occurs at the x-axis.

Areas of Agreement / Disagreement

Participants express differing views on where silence occurs in relation to the sine wave, with some asserting it is at the x-axis and others arguing it is not silent anywhere. The discussion remains unresolved with multiple competing perspectives on the nature of sound waves and auditory perception.

Contextual Notes

There are unresolved assumptions regarding the definitions of silence and sound, as well as the conditions under which sound is perceived versus measured. The discussion also touches on the complexities of sound wave behavior in practical applications.

ZB08
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Hi, easy one but can't really get my head around it. The physics teacher today showed sound as Sine wave on an oscilloscope. If I was actually listening to this sound wave, where would it be silent, on the x-axis or at the trough? Please explain.
 
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Sound is dependent on the amplitude, so it is zero on the axis.
 
If you are listening to it, you are "hearing the sound" with your brain. Not with your ears, and certainly not with a scientific measuring instrument! For almost all the frequency range where you hear anything at all, the loudness you hear will be constant.

On the other hand it we are talking about measuring what happens to the air wth scientific instruments rather than "what you hear", loudspeakers are designed so the position of the moving cone follows the voltage graph that you see on the oscilloscpe. (But a real loudspeaker isn't perfect, and won't follow it exactly). The change in air pressure, close to the speaker, is zero when the cone is at its mid point. However the velocity of the air close to the speaker is zero when the speaker is at the max and min displacements.

But further away from the speaker, there is a "time delay" because the speed of sound is finite - about 340 m/s so the peaks and troughs of the pressure and velocity further away from the speaker "lag behind" the movement of the speaker by an amount that is proportional to the distance away.
 
ZB08 said:
Hi, easy one but can't really get my head around it. The physics teacher today showed sound as Sine wave on an oscilloscope. If I was actually listening to this sound wave, where would it be silent, on the x-axis or at the trough? Please explain.

It wouldn't be silent anywhere. It would only be silent if there was no wave at all; just a flat line. At the x-axis the wave actually has the highest rate of change. The rate of change is zero at the peak and the trough but even then there would still be sound.
 
Thanks everybody
 

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