Does Sound Undergo a Phase Shift When Reflected From a Wall?

• Vibhor
In summary: On the other hand, a pulse arriving at a open circuit (=high impedance) will be reflected with the original phase.
Vibhor
Hello

When a mechanical wave gets reflected from a rigid surface,say a fixed end of a rope ,it undergoes a phase shift of ∏ ,but when a sound wave gets reflected from a hard surface ,say from a wall,it doesn't undergo any phase shift .

There is confusion regarding phase shift of sound wave from a hard surface,like a wall.At some places,I have read it doesn't undergo any phase change .At other places I have read ,sound undergoes a phase shift of ∏.

What is the correct explanation ?

Thanks

It depends on the relative impedance of the object that it's traveling in and reflected from...

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/reflec.html

When sound waves in air (pressure waves) encounter a hard surface, there is no phase change upon reflection. That is, when the high pressure part of a sound wave hits the wall, it will be reflected as a high pressure, not a reversed phase which would be a low pressure. Keep in mind that when we talk about the pressure associated with a sound wave, a positive or "high" pressure is one that is above the ambient atmospheric pressure and a negative or "low" pressure is just one that is below atmospheric pressure. A wall is described as having a higher "acoustic impedance" than the air, and when a wave encounters a medium of higher acoustic impedance there is no phase change upon reflection.

On the other hand, if a sound wave in a solid strikes an air boundary, the pressure wave which reflects back into the solid from the air boundary will experience a phase reversal - a high-pressure part reflecting as a low-pressure region. That is, reflections off a lower impedance medium will be reversed in phase.

Continues..

Electrical waves traveling down a transmission line are also phase changed (or not) according to the impedance of the end. For example a pulse arriving at a short circuit (=low impedance) is reflected inverted.

1. How does sound reflect from a wall?

Sound reflects from a wall when it hits the wall's surface and bounces off at an angle, similar to how a ball bounces off a hard surface. The angle of reflection is equal to the angle of incidence.

2. Why does sound reflect from a wall?

Sound reflects from a wall because sound waves are mechanical waves that can travel through different mediums, including air and solid objects. When sound waves reach a solid surface, they are reflected back due to a change in medium.

3. Does the material of the wall affect the reflection of sound?

Yes, the material of the wall can affect the reflection of sound. Hard, smooth surfaces like concrete and tile reflect more sound than soft, porous surfaces like carpet or curtains.

4. How does the distance between the sound source and the wall affect the reflection of sound?

The distance between the sound source and the wall can affect the reflection of sound. The closer the sound source is to the wall, the faster the sound wave will reflect and return. However, the intensity of the reflected sound decreases as the distance increases.

5. Can sound be absorbed by a wall?

Yes, sound can be absorbed by a wall. Soft, porous materials like acoustic panels or foam can absorb sound waves, reducing the amount of sound that is reflected back and preventing echoes in a room.

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