# Reflection of sound from open pipe

1. Feb 6, 2006

### abhijitlohiya

We know that when there is a change in medium there is reflection of sound.when it passsess through a pipe open at both end's , sound reflects.Actually the medium is same inside the pipe and outside the pipe, then how can we explain the reflection of sound from other end of pipe?

2. Feb 6, 2006

### DaveC426913

I don't follow what you're saying. "...the reflection of sound from other end of pipe..." What does this mean?

3. Feb 6, 2006

### DaveC426913

Regardless, you should examine two closely-related phenomena:

1] when waves of any kind pass an object (such as the rim of a pipe), they will refract (bend) around the object
2] waves that pass through a gap in an object, or any kind of hole (such as the opening on the end of a pipe) will act as if that is the point source of a new wave, spreading out in all directions.

4. Feb 6, 2006

### Danger

If you're referring to that 'hollow' sound, part of it is also reverberation of the pipe itself.
PS: While I can't speak for anyone else, I personally would ask you not to post in red. It's fine for highlights, but it hurts my ancient eyes to read much of it.

5. Feb 8, 2006

### abhijitlohiya

modification in the question

I mean when sound waves passing through pipe open at both ends ,it reflects from the open end boundry.if the medium and its density is same inside the pipe and outside the pipe, how the reflection of sound waves takes place?

6. Feb 8, 2006

### Staff: Mentor

Except for what has already been mentioned, the vast majority of the sound does not reflect back from the open boundary of the pipe.

7. Feb 8, 2006

### DaveC426913

Why don't you sketch us a diagram (2D) and upload it?

8. Feb 18, 2006

### gandharva_23

i think what abhijhit wants to ask is how are stationary waves formed in an open organ pipe . How does a ray get reflected from the open end ? is that you want to ask ?

9. Feb 18, 2006

### gandharva_23

amplitude of a standing wave ?

if two waves represented by equations y(x,t) = a sin(kx-wt) and y(x,t) = a sin(kx+wt) are superposed what will be the amplitude of the resultant wave . will it be 2asinkx or 2acoswt ? If i use the phasor method i do get 2acoswt but most of the books give it as 2asinkx .

10. Feb 18, 2006

### rbj

i think the issue here is about the sudden change of acousitical impedance at the end of the pipe.

think of a string that is tied to a brick wall at the far end (call that x=. send a wave down and it is inverted and reflected back

$$y(x,t) = f(x-ct) - f(x+ct)$$

were f(x) is the bump or waveshape far away from the reflection. and there are symmetry properties like f(-x)=f(x). that is like the pipe that is closed at the end and y(x,t) is the particle velocity (which has to be zero at the closed end).

now the open end pipe is more like a stretched out string that, instead of being tied to a brick wall on the far side, is tied to a slider of negligible weight on a pole that is perpendicular to the string and the friction of sliding up and down the pole is zero. then the wave equation for the particle velocity is

$$y(x,t) = f(x-ct) + f(x+ct)$$

in both the acoustical pipe and the stretched out string, what is happening is a sudden change of "transmission line" impedance of the medium or line. it's comparable to a transmission line with a short circuit or an open circuit at the far end.

Last edited: Feb 19, 2006
11. Jul 25, 2007

### abhijitlohiya

yes i mean the same.

12. Jul 25, 2007

### ZapperZ

Staff Emeritus
Maybe it would be a GOOD idea to NOT wait this long to come back and follow up on your question. A lapse of a year simply leaves the trail very cold.

Zz.

13. Jul 29, 2007

### Loren Booda

Nevertheless, I recalled and learned some interesting, albeit simple, acoustics from this thread.