Reflection of sound. Changes to its properties.

[buggsndirk]

Hi guys and girls,

Just had a question I have been thinking about for a while.

Suppose you have a sound maker than makes a pure tone at a particular frequency. You play this tone for an instant directed directly at a flat wall (not absorbent at all). If you could measure the reflected tone would there be any change in frequency, intensity, wavelength or velocity?

My gut feeling is that the intensity will lower somewhat, but nothing else will change, but I have a feeling I'm missing something super obvious like a doppler effect or something.

Any and all thoughts are appreciated.

Thanks

 

[maajdl]

Is this wall moving?
If it is moving away, then each wavelength will be reflected a little bit later, which is the Doppler effect (called red shift).
If it is moving toward you, the each wavelength will be reflected a little bit earlier, also the Doppler effect (blue shift).

 

[buggsndirk]

Everything is stationary.

so nothing will change?

 

[Bobbywhy]

At longer distances from the reflecting surface, the only difference you will measure is some decrease in intensity, as you said in your Opening Post (OP). But, measure the sound intensity very close to the reflecting surface...expect a surprise!

“Sound intensity near a hard surface is enhanced because the reflected wave adds to the incident wave, giving a pressure amplitude that is twice as great in a thin "pressure zone" near the surface. This is used in pressure zone microphones to increase sensitivity. The doubling of pressure gives a 6 decibel increase in the signal picked up by the microphone.”
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/reflec.html

 

[sardar]

for your question! Reflection of sound is a fascinating topic and there are definitely some interesting properties to consider when it comes to changes in frequency, intensity, wavelength, and velocity.

First, let's talk about the reflection of sound waves. When a sound wave hits a flat wall, it will bounce off and travel back in the opposite direction. This is known as reflection. The angle at which the sound wave hits the wall is called the incidence angle, and the angle at which it bounces off is called the reflection angle. The incidence angle and the reflection angle are always equal.

Now, to address your question about changes in frequency, intensity, wavelength, and velocity. The short answer is that all of these properties will remain the same after the sound wave is reflected off the wall. This is because the sound wave is simply bouncing off the wall and not interacting with any other medium that could cause changes in its properties.

However, there are a few factors that could potentially affect the reflected sound wave. One is the shape and texture of the wall. If the wall is not completely flat and smooth, it could cause some scattering of the sound wave, leading to changes in intensity and possibly frequency. Additionally, if the wall is made of a different material than the medium through which the sound wave is traveling, there could be some absorption of the sound wave, leading to a decrease in intensity.

Another factor to consider is the distance between the sound source and the wall. As the sound wave travels back and forth between the source and the wall, there could be some interference patterns that could affect the intensity and possibly the frequency of the reflected wave.

Overall, the changes in properties of a reflected sound wave will be minimal and likely not noticeable to the human ear. However, as a scientist, it is important to consider all factors and variables when studying sound and its interactions with different mediums. I hope this helps clarify some of your thoughts and please let me know if you have any further questions.