Speaker amplitude should not be affected by air density in Air Pressure screen

[matthew-blackman]

In the Air Density screen, removing air from the box should not affect the vibration of the speaker. In the java sim, the speaker continues to vibrate even when air is removed from the box.

[matthew-blackman]

In the below example, the behavior of the waves is correct but the speaker should continue vibrating at the same amplitude and frequency when air is removed from the box.

[matthew-blackman]

This was a straightforward change and has been fixed with the above commit. Closing.