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Audio wave question??????

post #1 of 22
Thread Starter 
I am considering adding two more speakers to my surround sound.

Because all my speakers are in-ceiling, I am not able to test to make sure there aren't any problems.

I want to add a left and right speaker. The sound wave of both speakers will intersect and cross through other speaker sound waves in the system.

Does this wave cross over create any problems with the sound/wave, any distortions?????

I don't think it will but before spending $$$ and cutting holes in the ceiling, I want other's opinions that know more about this than I do.

Thanks



m
post #2 of 22
If you care about sound quality, forget speakers in the ceiling. That's about the worst place you could have them. This short article explains more:

How to set up a room

--Ethan
post #3 of 22
Thread Starter 
Quote:
Originally Posted by Ethan Winer View Post

If you care about sound quality, forget speakers in the ceiling. That's about the worst place you could have them. This short article explains more:

How to set up a room

--Ethan

I thank you for your concerns. Yes, I already know the differences between towers and in-ceiling speakers.

There are times one does not have a choice and what is has to be.

Now back to my question:

Are there problems with sound wave cross through each other?
post #4 of 22
Thread Starter 
I have read a lot of sound wave web sites yesterday. Here is some information


It is the nature of waves in any medium to pass through each other without disrupting each other. If you picture intersecting hallways with a 1 khz wave (Freq 1) going South and a 2 khz wave (Freq 2) gong East, each wave will reach its listener with no disruption. If Listener A could only hear at 1 khz and Listener B could only hear at 2 khz, neither would even have a way of knowing that the other wave crossing through his own wave existed. There would be no loss or distortion resulting from the superposition of the waves at the intersection.



At the intersection of the hallways, a microphone would let you see how the sound pressures of the two waves combine as they pass through each other. You would get a different measurement for every position of the microphone at the intersection. If Freq 2 was switched to 1 khz and both waves were the same amplitude, then there would be complete cancellations at some points in the intersection. At other points the waves would add together and the amplitude would be doubled. Still, each listener would hear his own wave with no disruption by the other.

There are real world situations where we ignore this out of practicality. A concert PA system will have flying left and right speaker columns both running the same signal during the concert, but because of the reverberant acoustics of the arena, with reflections all over the place, there are so many intersecting waves at any one point that the result is mostly additive with very little cancellation taking place. In our listening rooms it can be a problem.



From the above it sounds like if two sound waves cross path and they are the same sound wave, they will cancel each out, a collision, a distortion. But because the waves that cross each other are different, there isn't any collision or distortion.

This is my understanding from the above excerpt from an article.

Do you agree?


m
Edited by JimShaw - 6/9/13 at 8:45am
post #5 of 22
multiple post
post #6 of 22
multiple post
post #7 of 22
multiple post - why no option to delete post?
post #8 of 22
Quote:
Originally Posted by JimShaw View Post

Are there problems with sound wave cross through each other?
Acoustic interference occurs all the time, with speakers placed anywhere, and is also caused by direct sound from the speakers combining with sound reflected off the walls, floor and ceiling. So your scenario isn't really any different, if that's what you're asking. But the answer is Yes, such interference creates peaks and nulls in the response.

--Ethan
post #9 of 22
Thread Starter 
Here is an excerpt from a physic forum talking about sound waves that pass through each other

Interestingly, the meeting of two waves along a medium does not alter the individual waves or even deviate them from their path. This only becomes an astounding behavior when it is compared to what happens when two billiard balls meet or two football players meet. Billiard balls might crash and bounce off each other and football players might crash and come to a stop. Yet two waves will meet, produce a net resulting shape of the medium, and then continue on doing what they were doing before the interference.

It seems from the above that meeting waves pass through each other, changes the shape of both waves and then once through, the wave reverts back to the original shape and path.

This is my understanding, yours also?

If this is so, I can install two more speakers that will cross path with two others and all will be OK. Oh, happy day.



mm
Edited by JimShaw - 6/9/13 at 11:07am
post #10 of 22
Quote:
Originally Posted by JimShaw View Post

Here is an excerpt from a physic forum talking about sound waves that pass through each other

Interestingly, the meeting of two waves along a medium does not alter the individual waves or even deviate them from their path. This only becomes an astounding behavior when it is compared to what happens when two billiard balls meet or two football players meet. Billiard balls might crash and bounce off each other and football players might crash and come to a stop. Yet two waves will meet, produce a net resulting shape of the medium, and then continue on doing what they were doing before the interference.

It seems from the above that meeting waves pass through each other, changes the shape of both waves and then once through, the wave reverts back to the original shape and path.

This is my understanding, yours also?

If this is so, I can install two more speakers that will cross path with two others and all will be OK. Oh, happy day.



mm

aka: Comb Filtering. All sounds that comes from a multiple sources (or single source reflected) have some degree of comb filtering. Also add in 1st reflections, 2ed reflections, 3rd reflections,..., corner reflections....., the list is endless. The human brain has an excellent comb filter built in and has been dealing with this since birth. Only hard core audiophiles with high quality room/equipment need to be concerned with comb filtering. If using in celling speakers comb filtering should 1000's of steps down the ladder of your worries.

Here is a good short article.
post #11 of 22
Thread Starter 
Quote:
Originally Posted by William View Post

aka: Comb Filtering. All sounds that comes from a multiple sources (or single source reflected) have some degree of comb filtering. Also add in 1st reflections, 2ed reflections, 3rd reflections,..., corner reflections....., the list is endless. The human brain has an excellent comb filter built in and has been dealing with this since birth. Only hard core audiophiles with high quality room/equipment need to be concerned with comb filtering. If using in celling speakers comb filtering should 1000's of steps down the ladder of your worries.

Here is a good short article.

Thanks, I am linking over to read.


Very interesting. So, from the article, it seems that if there is a slight corruption, our brain will filter it out.



m
Edited by JimShaw - 6/9/13 at 3:08pm
post #12 of 22
Thread Starter 
Quote:
Originally Posted by Ethan Winer View Post

Acoustic interference occurs all the time, with speakers placed anywhere, and is also caused by direct sound from the speakers combining with sound reflected off the walls, floor and ceiling. So your scenario isn't really any different, if that's what you're asking. But the answer is Yes, such interference creates peaks and nulls in the response.

--Ethan


Ethan

From what I think you are saying is: Sound waves are bouncing and crossing each other all around a room from speakers and two more speakers' wave crossing paths won't do any more than what is already happinging, correct?


m
post #13 of 22
regarding your question on the behavior: the sound waves produced from real sources (additional speakers) or virtual sources (indirect reflections from room boundaries) do not directly affect each other, but they do affect the total response at a given location in 3-space.

two or more spaced sources will superpose (combine) to create an interference pattern at a given wavelength, and spatial polar lobing will develop.
  • the polar lobes correspond to areas of constructive interference, and would result in a peak within the frequency response.
  • the polar nulls correspond to areas of destructive interference (out-of-phase cancellation), and would result in a null within the frequency response.

the series of peaks and nulls across a given bandwidth at a given location in the room corresponds to the "comb-filtering" as viewed in the 2D frequency response - but it's important to note that comb-filtering itself is not "real". it does not exist in the real world and is simply an interference pattern generated within the frequency-response. what is "real" is the 3D spatial polar lobing.


here are some 2dimensional wave tank examples illustrating the spatial polar lobing developed from two spaced sources (eg, two loudspeakers) in isolation. notice how wavelength size changes the pattern of polar lobes changes (the spacing and their number).

Sn0Y3iV.png

9zYB8Y4.png

fUroK6z.png

b9W0Een.png


and here is an example of the developed polar lobing from a single loudspeaker and an indirect reflection via that of a rigid boundary:

xExH4do.jpg
post #14 of 22
Thread Starter 
Quote:
Originally Posted by localhost127 View Post

regarding your question on the behavior: the sound waves produced from real sources (additional speakers) or virtual sources (indirect reflections from room boundaries) do not directly affect each other, but they do affect the total response at a given location in 3-space.

two or more spaced sources will superpose (combine) to create an interference pattern at a given wavelength, and spatial polar lobing will develop.
  • the polar lobes correspond to areas of constructive interference, and would result in a peak within the frequency response.
  • the polar nulls correspond to areas of destructive interference (out-of-phase cancellation), and would result in a null within the frequency response.

the series of peaks and nulls across a given bandwidth at a given location in the room corresponds to the "comb-filtering" as viewed in the 2D frequency response - but it's important to note that comb-filtering itself is not "real". it does not exist in the real world and is simply an interference pattern generated within the frequency-response. what is "real" is the 3D spatial polar lobing.


here are some 2dimensional wave tank examples illustrating the spatial polar lobing developed from two spaced sources (eg, two loudspeakers) in isolation. notice how wavelength size changes the pattern of polar lobes changes (the spacing and their number).

Sn0Y3iV.png

9zYB8Y4.png

fUroK6z.png

b9W0Een.png


and here is an example of the developed polar lobing from a single loudspeaker and an indirect reflection via that of a rigid boundary:

xExH4do.jpg


I am starting to think this is a difficult decision because of the difficulty understand hard to understand definitions. I read information that are written by an electronic engineers and I find it very hard to really grasp: Will or won't two sound waves that cross path in a surround sound hurt the sound??? Or will they pass through and any change that happens will not be noticed by the listener?



m
post #15 of 22
Quote:
Will or won't two sound waves that cross path in a surround sound hurt the sound??? Or will they pass through and any change that happens will not be noticed by the listener?

The crossing of sound waves is the least of your problems. The problems is reflections of multiple orders and their interaction with the direct and reflected sound waves when radiated from different sources.
post #16 of 22
Hi Jim,
Quote:
Originally Posted by JimShaw View Post

From the above it sounds like if two sound waves cross path and they are the same sound wave, they will cancel each out, a collision, a distortion. But because the waves that cross each other are different, there isn't any collision or distortion.

This is my understanding from the above excerpt from an article.

Do you agree?
Close, but not close enough.

What the article is saying that there is no distortion to each wave as they pass through each other. Whether or not they are the "same" sound wave will make no difference.

The cancellation occurs only at the intersection of the two waves, and then there are both cancellations where the two waves are out-of-phase, and reinforcement where the two waves are in-phase. That is only because you are hearing (or measuring) both waves added together. Once the sound waves get past the intersection, they are as they were before the intersection.

LocalHost's post shows the cancellations and reinforcements well. In his pictures (except the last), the whole area would be in the intersection. Most of your room would be in the intersection, so although the waves are not being affected by the other waves, what you hear is affected by the fact that the waves are being "summed" at your ears, and that summation is different at every location in your room.
post #17 of 22
Thread Starter 
Quote:
Originally Posted by MarkHotchkiss View Post

Hi Jim,
Close, but not close enough.

What the article is saying that there is no distortion to each wave as they pass through each other. Whether or not they are the "same" sound wave will make no difference.

The cancellation occurs only at the intersection of the two waves, and then there are both cancellations where the two waves are out-of-phase, and reinforcement where the two waves are in-phase. That is only because you are hearing (or measuring) both waves added together. Once the sound waves get past the intersection, they are as they were before the intersection.

LocalHost's post shows the cancellations and reinforcements well. In his pictures (except the last), the whole area would be in the intersection. Most of your room would be in the intersection, so although the waves are not being affected by the other waves, what you hear is affected by the fact that the waves are being "summed" at your ears, and that summation is different at every location in your room.

That seems to be my understand also.

Therefore, after the waves pass through each other, each wave will not be distorted as they move towards the listener's ears? It will be as if there wasn't any collision, correct?
post #18 of 22
The waves would pass through OK, if there were only a local region of crossing. That isn't the case though. With two speakers playing into a room, for all practical purposes each speaker "illuminates" the entire room, so each point within it is at a crossing.

Think of it this way... no matter where you sit, sound from both speakers will reach both of your ears, and what you hear is the summation or the interference patter at that particular location. That's OK... that is how we hear "stereo". Unless you are asking something else that isn't clear.
post #19 of 22
Hi Jim,
Quote:
Originally Posted by JimShaw View Post

Therefore, after the waves pass through each other, each wave will not be distorted as they move towards the listener's ears? It will be as if there wasn't any collision, correct?
Correct, but:
Quote:
Originally Posted by Bigus View Post

The waves would pass through OK, if there were only a local region of crossing. That isn't the case though.
As Bigus points out, your whole room is an area where the waves are intersecting. So what you hear is a "summation" of all of the waves at the two points in the room where you place your ears. The waves include the primary waves from the speakers, and a lot of supplemental waves from reflections. That summation will be unique at every point in the room, which is why so many of us setup our system to sound best at the primary listening position.

Another way to look at it is that the each of the many waves are undisturbed by each other when they reach your ears from every direction, but what you hear is not the individual waves, but the combination of them all at each ear.

That original diagram with the crossing hallways is overly simplistic in that it assumes no reflections, so each listener only hears one source. There is no summation of waves taking place.
post #20 of 22
Quote:
Originally Posted by JimShaw View Post

From what I think you are saying is: Sound waves are bouncing and crossing each other all around a room from speakers and two more speakers' wave crossing paths won't do any more than what is already happinging, correct?

Yes, exactly, though this doesn't mean that the resulting skewed response is desirable or even acceptable! That's why proper listening rooms have acoustic treatment - either absorbers or diffusers or both.

--Ethan
post #21 of 22
Thread Starter 
My decision has been made. What helped was the price I was able to get two AIM8 Fives. Best Buy's price after a special order would be $1794.75.

I was able to find two new speakers shipped for $615.16.

For that price, I will test. If good, great. If not, I'll sell and probably make a profit.

I'll let you know.



m

Edited by JimShaw - 6/11/13 at 10:22pm
post #22 of 22
Quote:
Originally Posted by JimShaw View Post

My decision has been made. What helped was the price I was able to get two AIM8 Fives. Best Buy's price after a special order would be $1794.75.

I was able to find two new speakers shipped for $615.16.

For that price, I will test. If good, great. If not, I'll sell and probably make a profit.

[/COLOR]

$600 for a couple of 8 inch woofers and 1 inch dome tweeters?

Well, far better than $1,800 for the same thing.
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