Originally Posted by jarrod1937
When does phase shifting/reversal happen with sound waves? If a sound wave of a particular phase hits a wall, is its phase effectively reversed? Does its wavelength affect its phase, both alone and when being inverted?
If the transmission medium abruptly changes from high impedance to low the reflection will change polarity. No. No.
When acoustic waves hit a boundary going from low acoustic impedance to high impedance, the reflections are positive - a high-pressure pulse is reflected as a high-pressure pulse (regardless of wavelength). At a boundary going from high impedance to low impedance the reflections are negative - the reflection of a high-pressure pulse is a low-pressure pulse.
Acoustic impedance (Z) of a material is its density times its acoustic velocity. Since air is low density and has low acoustic velocity compared to, say, sheetrock or wood or plaster, the reflection off the face of the sheetrock (wood, plaster) will be positive.
This is the basic principle behind reflection seismology used in oil exploration, by the way, only there you are looking at reflections caused by slight differences between the Z of different layers of rock. See the Wikipedia article on Reflection Seismology
for more information - the same principles apply, only the reflection coefficients here are huge (almost 100% due to vast differences in Z) and always positive (from air to something solid - low-Z to high).
The wiki article on Reflection Coefficient
has a good illustration of a reflection off a boundary with negative coefficient of reflection
. Note that the reflected portion has opposite polarity, and the transmitted portion moves more slowly and has shorter wavelength (due to lower velocity).