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Posted: Tue Aug 22, 2006 10:18 pm
by ChrisWerner
I have a question in my mind and I can´t find an answer, or at least no real explaining answer.
A sonic vibration or oscillation, let´s say a sine, hits a wall and gets reflected.
It hits the wall with 0 degree.
Does the sine turn its phase or not.
Does it come back with a 180 degree turned phase?
<font size=-1>[ This Message was edited by: ChrisWerner on 2006-08-22 23:19 ]</font>
Posted: Wed Aug 23, 2006 1:12 am
by Gordon Gekko
i'd say yes, like a ball hitting a wall would do, or a wave in a pool. but hey, my physics manuals have been lost for a long time
Posted: Wed Aug 23, 2006 2:01 am
by Counterparts
I not sure if you've quite visualised the problem correctly.
I think that you're thinking of a sine wave travelling towards the wall, going up and down nicely (like all good sine waves do).
However, what's really happening is the air is being compressed and expanded (forming the wave) in the direction that the sound is travelling in. That waveform will be reflected off the wall, the 'phase' not being changed at all; the wave carries on as it was before, with loss of energy depending on the wall's surface.
Posted: Wed Aug 23, 2006 12:16 pm
by Immanuel
I believe it goes something like this:
Code: Select all
__ __
/ W/
/ /A
/ / L /
__/ __/ L __/
It does not go up and down, but think of the wave as high and low preasure points. And all here is caught in time over a distance. What you have to do is to mirror the stuff that passes thru the wall on my little thing above.
Code: Select all
__ __ __
/ / / W
/ / / /A
/ / / / L
/__/ __/__/ L
and then sum it up, because there is only one airpreasure at a certain point at a certain time ...
Code: Select all
Sorry - I have to change to numbers here. The low _ will have value 0 the high _ will have value 4.
1-1-1½-2-2½-3-3-3-2½-2-1½-1-1-1-1½-2-2½-3-3-3-...
but "one sample" later you will have:
[code]
__ __ __
/ / / W
/ / / A
/ / / /L
__/ __/ __/ L
wich translates into
0-0-0-0-0-0-0-0-0-0-0-0-0
and you can make more drawings, if you want to. If you do so, you will se, that this sine wave with this size of room will be able to reach both 0 and 4, when you sum things up. These drawings are however rather square ... and not really sine.
I don't know, if this answers your question.
Posted: Wed Aug 23, 2006 12:41 pm
by hubird
jeez!...
good typing
Posted: Wed Aug 23, 2006 12:50 pm
by ReD_MuZe
the phase by hitting the wall is reversed.
as it is reflected to the oposite direction
Posted: Wed Aug 23, 2006 3:01 pm
by astroman
c'mon - it's about a tone, not a laser...
(I mean the setup, not your answer, Red)
<font size=-1>[ This Message was edited by: astroman on 2006-08-23 16:02 ]</font>
Posted: Wed Aug 23, 2006 9:39 pm
by ChrisWerner
Thank you very much for your answers, the correct answer is that it does not change the phase.
But we have an on going little war at school about this one, our lecturer didn´t gave us a real reason, yet. I will keep you in touch.
_________________
Music starts where any language ends<br>
<a href="http://www.spring-of-sound.de">Spring-Of-Sound.de</a>
<font size=-1>[ This Message was edited by: ChrisWerner on 2006-08-24 00:17 ]</font>
Posted: Wed Aug 23, 2006 9:42 pm
by ChrisWerner
I think / thought like immanuel draw us so nicely.
_________________
Music starts where any language ends<br>
<a href="http://www.spring-of-sound.de">Spring-Of-Sound.de</a>
<font size=-1>[ This Message was edited by: ChrisWerner on 2006-08-23 22:43 ]</font>