Maximum Amplitude of Sound Wave?

[tade]

This animation demonstrates a longitudinal wave by means of moving bars.



I realized that if we increase the amplitude of the wave, the bars will eventually start passing through each other, which sounds (no pun intended) like an unphysical scenario.

Does this mean that there is a cap, a maximum amplitude to this simulation? Is there a real world equivalent to this, a maximum loudness?

 

[mfb]

The bars are just for illustration, they don't have a width.

There is no relevant upper limit for air pressure, but there is a lower limit - zero. Once the sound gets too loud, you don't get classical sound (with symmetric pressure changes) any more, but you can still have shockwaves (very large pressure). This limit for normal sound would roughly correspond to 190 dB.

 

[tade]

The bars are just for illustration, they don't have a width.

Are you referring to the width of each bar or the spacings between the bars?

 

[mfb]

The widths of the bars.

 

[tade]

The widths of the bars.

Ok, I'd assumed that the bars were just lines of zero thickness.

But when they oscillate at a large enough amplitude, in the simulation, they pass through one another.

 

[mfb]

But when they oscillate at a large enough amplitude, in the simulation, they pass through one another.

No they do not. At least not if the animation is good. In the video they don't pass each other.

 

[tade]

No they do not. At least not if the animation is good.

When there are no waves, the lines are evenly spaced, with a default spacing width.

Now a longitudinal wave starts. The frequency and wavelength remain fixed.

But if we keep increasing the amplitude of each bar's oscillation around its default position, wouldn't they collide with each other eventually?

 

[mfb]

Well, eventually you'll run into the same problem as with air. You would need regions of 0 bar density, and that you cannot have with this bar model.
As long as the bars properly show the motion of air, they don't collide.

 

[tade]

Well, eventually you'll run into the same problem as with air.

What happens when we reach that situation with air in real life?

 

[mfb]

See above, you get shockwaves.

 

[Tom.G]

Those bars in the animation represent air density, not necessarily air movement. When the amplitude passes about 190db, as @mfb pointed out, the simulation would/should show NO bars at the troughs. As the amplitude increased above 190db, the width of the vacuum region (region with no bars) would widen, approaching 1/2 wavelength at the limit. Of course the real-world details may vary a bit, it is hard to get a perfect vacuum.

See, starting around the 1 min. mark:

 

[tade]

Those bars in the animation represent air density, not necessarily air movement.

In that case, is it correct to say that while the pressure increases by large increments, the displacement amplitude (units of length) only increases by tiny increments?

 

[tade]

See above, you get shockwaves.

Ok thanks. Are they the supersonic kind?

https://en.wikipedia.org/wiki/Shock_wave

 

[Tom.G]

In that case, is it correct to say that the pressure increases by large increments while the displacement amplitude (units of length) only increases by tiny increments?

Okay, I would call that a valid conclusion. For a different physical example see the below video. The central particles barely move but the pressure (force) on the central ones obviously has to increase substantially at certain moments.