# Audio wave question??????



## JimShaw (Apr 30, 2012)

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 are problems.

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

Do audio waves crossing through each other 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


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## AudiocRaver (Jun 6, 2012)

JimShaw said:


> Do audio waves crossing through each other create any problems with the sound/wave, any distortions?????m


When more than one speaker is running the same signal, you get phase cancellations at different frequencies depending on the listening location. In other words, the frequency response is different wherever you are in the room. Depending on the room it can be anywhere between a minor annoyance and a major headache. The approach is generally not recommended where sound quality is a priority.

If each speaker in the system is running its own signal, like from a surround mix, this is not an issue.


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## JimShaw (Apr 30, 2012)

AudiocRaver said:


> When more than one speaker is running the same signal, you get phase cancellations at different frequencies depending on the listening location. In other words, the frequency response is different wherever you are in the room. Depending on the room it can be anywhere between a minor annoyance and a major headache. The approach is generally not recommended where sound quality is a priority.
> 
> If each speaker in the system is running its own signal, like from a surround mix, this is not an issue.


I did a search through a few web sites that talked about "What Happens When Two Sound Waves Collide"

You're right they can cancel each other out.

But your sentence interested me...
*
If each speaker in the system is running its own signal, like from a surround mix, this is not an issue.*

If I set in a left and right surround speakers and that wave passed through left and right Wides (the Wide wave would be from the front sound stage whereas the surrounds are playing the back sound stage), would that be considered enough of its own mix to not create a collision???

I hope I made sense and I hope you reply.

I have posted this thread on three forums because I need to know. Out of three, there has been many reads but you are the only poster that has replied. 

Thanks

-----------------------------------------

Here is something I found...

*What Happens When Two Sound Waves Collide*
I guess you have to be a real audio techie to read this post, but I think it’s interesting stuff.

Most sound sources produce energy at multiple frequencies and different sound sources often combine. When this happens it is the more complex, composite, waveform that we hear. This combination of different overtones and sound changes the resulting wave shape. The term interfere or superposition is used to describe what happens when waves pass through each other or are superimposed.

If the two sound waves that collide are exactly in phase with each other they add together and produce a sound wave that is twice as loud. If they are exactly (180°) out of phase, they cancel each other out and the result is silence. If they two waves differ in amplitude the new sound wave is different in amplitude from either of them.

Let’s consider a real world situation where phase cancellation can occur. Suppose you place the speakers on a P.A. system too close to a live sound source such as a set of drums. The speakers might cancel out some of the sound of the drums by overlapping the natural sound of the drums with the amplified sound. The illustration below shows what happens when sound waves that are exactly in phase, 180° out of phase, and of different amplitudes, collide. Sources: Real World Digital Audio by Peter Kirn (Peach Pit Press, 2006, and mediacollege.com.

-------------------------------------------

Does this make sense to anyone?????





m


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## AudiocRaver (Jun 6, 2012)

It is a fun topic, one we don't think about in detail very often.

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.



JimShaw said:


> If I set in a left and right surround speakers and that wave passed through left and right Wides (the Wide wave would be from the front sound stage whereas the surrounds are playing the back sound stage), would that be considered enough of its own mix to not create a collision???


If you are connecting the speakers to the Surround and Front Wide outputs of a modern AVR with built-in listening modes, the signals generated for those speakers will be different enough that phase cancellations will not be a problem. Those listening modes have been designed with just these questions in mind.


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## JimShaw (Apr 30, 2012)

AudiocRaver said:


> It is a fun topic, one we don't think about in detail very often.
> 
> 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.
> 
> ...



AudiocRaver

I really want to thank you for your help and information.

I was getting very disappointed because I did not think it would work. From what info. I could gleam sounded (to this very novice audiophile) that the waves would collide and distort the sound. THAT would not make me happy. 

This is something that I did not want to do without some type of understanding that all would/should work. The speakers are too expensive for a test run. Both speakers purchased from an authorized dealer will cost over $800 each and at the same time, holes cut into the ceiling. Not a happy thing for my wife if I had to pull the speakers out from not working correctly.

It seems to me from reading the above that if all 4 speakers were playing the same sound, THEN there will be a cancellation, a collision. But because the sound waves that cross path with each other are different, they pass through without distortion. This is what I hear you saying, correct?

If this is so, I will gamble and go for it. 

There is this one sentence in the article: *In our listening rooms it can be a problem.* This does make me worry a little. But if I read that section, it is talking, once again, about sound waves that are alike not waves that cross path and different, correct?

Thanks




m


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## JimShaw (Apr 30, 2012)

Here is another excerpt from a physic forum talking about sound waves.


*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?



m


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## AudiocRaver (Jun 6, 2012)

JimShaw said:


> Here is another excerpt from a physic forum talking about sound waves.
> 
> 
> *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.*
> ...


Precisely.


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## JimShaw (Apr 30, 2012)

AudiocRaver said:


> Precisely.


Excellent.

I will be spending $$$$ tomorrow and order. It will take me awhile to get them, install, etc. When I do, I will get back and let you know the outcome.

I really thank you for your help


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## Gregr (Nov 2, 2010)

JimShaw said:


> Here is another excerpt from a physic forum talking about sound waves.
> 
> 
> *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.*
> ...


This quote is confusing and incomplete and really in need of clarification. The reality of all this is simple. Sound waves from two or more sources are additive or subtractive and every value in between when waves of equal frequency meet. The variability is dependent upon distance (spatial position), timing, amplitude and phase. For as long as the combined notes are interacting any continuing variability result will continue and play out to infinitude. Any unaffected or original note remaining will play through to infinitude. The effect of the interaction is permanent only on that portion affected.

To see how waves will combine, add and subtract - use a Pyrex baking dish and 1" of water. To make it interesting put an obstacle in the dish as well. Now tap the water with your fingers. Tap with equal frequency and timing see how waves combine or alter the timing..., you get the pic

But that's not the final word. Remember this is mostly problematic when playing a two channel recording thru 4, 6, or 8 speakers and even then may not be noticeable except incases where you are expecting a specific note. I don't know about anybody else but I do not have perfect pitch so I probably will not notice 98% of any notes affected. If I did and this became a problem I could adjust delay..., I have never done this in my life. 

Better yet, room treatment is always a good idea and there is Adyssey EQ XT or any variation there-of. I'd be more concerned with speaker placement. What is wrong with floor standing towers $1600 will buy a very decent pair of speakers?

Regards


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## JimShaw (Apr 30, 2012)

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.


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## Gregr (Nov 2, 2010)

Oh, one more thing. When sound waves pass at 90 degrees one is not effected by the other as described earlier. One wave will ride over the other and each wave remains intact, unaffected. Again if you use the water in the dish example you can plainly see this happen. There is an interaction with some distortion but each and every note plays through.

Pretty amazing, I'm with ya on that.

Regards


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