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Author Topic: "Multi cellular array" vs "Single Source array"  (Read 25874 times)

Ivan Beaver

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Re: "Multi cellular array" vs "Single Source array"
« Reply #40 on: July 23, 2016, 09:39:00 am »


In this case it is one compromise to utilize a secondary enclosure to gain additional HF because it creates a distance between the primary enclosure and the secondary.  If air absorption is creating an acoustic crossover at 4kHz from the main cabinet and the additional HF cabinet is augmenting that beggining at 4kHz then those cabinets would need to be within 1.685" vector delta centerline of HF to centerline of HF in order to avoid comb-filtering.

Maximum comb filtering happens when both signals are the same level

When one level goes down, the amount of interference goes down.

In this case- the HF cabinet is MUCH louder than the full range cabinet.

Since there is nobody within 700' or so of the cabinets-this level difference is not important at those closer distances.

Is this approach perfect-no.  But no line array could possibly get the HF out to those seats at that distance as well.

But that is EXACTLY why there is now a much louder approach, that is a single cabinet (using 108 drivers) to "reach out and touch" those seats, that is being used in the large stadiums.

The latest one is being installed at FSU as we speak
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Ivan Beaver
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Lee Buckalew

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Re: "Multi cellular array" vs "Single Source array"
« Reply #41 on: July 23, 2016, 11:46:33 am »

Maximum comb filtering happens when both signals are the same level

When one level goes down, the amount of interference goes down.

In this case- the HF cabinet is MUCH louder than the full range cabinet.

Since there is nobody within 700' or so of the cabinets-this level difference is not important at those closer distances.

Is this approach perfect-no.  But no line array could possibly get the HF out to those seats at that distance as well.

But that is EXACTLY why there is now a much louder approach, that is a single cabinet (using 108 drivers) to "reach out and touch" those seats, that is being used in the large stadiums.

The latest one is being installed at FSU as we speak

Understood Ivan, not picking apart a specific design, merely answering some of Yoel's questions regarding what are the compromises involved. 

The same issue however does not present with a level difference in the horizontal plane when butting two coverage patters to extend width of coverage, nor does a level difference present itself at the crossover region between a full range cabinet and HF supplemental devices. 
Usually the distance involved, as has been pointed out in this thread, where the supplemental HF is needed creates a vector delta that eliminates the comb-filter or moves it's starting point to a high enough frequency that air absorption stops it from being heard although, if it is present, even though not heard, it will, as has also been previously pointed out, create nulls and peaks that create non-coherent propagation and limit "throw". 
If the comb-filtering can be eliminated then the coherence of the acoustic signal is maintained and greater "throw" is achieved. 

That is what you guys are doing with larger and larger coherent horn devices and that is what MLA is doing with a combination of driver, cabinet, and processing designs/implementation.  I do not have access to it right now but Left Right hangs of full size MLA have been utilized for coverage of between 700' - 900' with minimal variation up to 12.5kHz.  Memory says less than +/-3dB but I certainly may be remembering incorrectly.

Lee
« Last Edit: July 23, 2016, 03:06:56 pm by Lee Buckalew »
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Mac Kerr

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Re: "Multi cellular array" vs "Single Source array"
« Reply #42 on: July 23, 2016, 12:05:50 pm »

It is not the physical distance between the elements that causes comb filtering.  But rather the distance in time between the elements that the listener hears.

Since the closest listener for these cabinets is around 700' away, the signal arrival time difference are very small.

Very much like the listeners far from a line array who are hearing multiple elements of high frequency vs close listeners who are hearing fewer.

Mac
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Ivan Beaver

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Re: "Multi cellular array" vs "Single Source array"
« Reply #43 on: July 23, 2016, 12:22:50 pm »

  I do not have access to it right now but Left Right hangs of full size MLA have been utilized for coverage of between 700' - 900' with minimal variation up to 12.5kHz.  Memory says less than 3dB but I certainly may be remembering incorrectly.

Lee
I have a VERY HARD time believing that you are getting out to 12K with anywhere near a 3dB variation at 900'.

When you consider that the normal difference between 10M and 300M is around 29dB.  When you add air absorption (Yes it does vary with humidity and temp), that become 74dB-give or take good bit.

That is a HUGE HUGE HUGE difference to make up with DSP.

In the particular case in question, the coverage pattern of the "tweeters" was 30* wide x 10* tall.  NO attempt was made to try to cover the near seats-in fact we wanted to miss them as much as possible-due to the levels being in excess of 160dB coming out of the "tweeters". 

There were 256 1" compression drivers pointed just towards the rear seats on large horns.

The main cabinets got to around 4Khz and pretty much died at those seats.

The "tweeters" got us up to 8Khz.  There was really nothing going beyond that.
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Ivan Beaver
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Ivan Beaver

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Re: "Multi cellular array" vs "Single Source array"
« Reply #44 on: July 23, 2016, 12:26:18 pm »

Very much like the listeners far from a line array who are hearing multiple elements of high frequency vs close listeners who are hearing fewer.

Mac

It depends on the freq involved.   Yes-in the top octave, the small horns (relative to the coverage pattern) will control the sound and keep the levels down for people out of the pattern, but as the freq goes down, they will lose pattern control and people will hear the multiple arrivals at close seats.

What this results in is a "smearing" of the sound, that will make transient things not seem as real.  ESPECIALLY percussive instruments and picked instruments.

Blown or bowed instruments will not suffer as much.

The "detail" is what goes missing when you have multiple arrivals
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Lee Buckalew

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Re: "Multi cellular array" vs "Single Source array"
« Reply #45 on: July 23, 2016, 12:49:53 pm »

I have a VERY HARD time believing that you are getting out to 12K with anywhere near a 3dB variation at 900'.

When you consider that the normal difference between 10M and 300M is around 29dB.  When you add air absorption (Yes it does vary with humidity and temp), that become 74dB-give or take good bit.

That is a HUGE HUGE HUGE difference to make up with DSP.

In the particular case in question, the coverage pattern of the "tweeters" was 30* wide x 10* tall.  NO attempt was made to try to cover the near seats-in fact we wanted to miss them as much as possible-due to the levels being in excess of 160dB coming out of the "tweeters". 

There were 256 1" compression drivers pointed just towards the rear seats on large horns.

The main cabinets got to around 4Khz and pretty much died at those seats.

The "tweeters" got us up to 8Khz.  There was really nothing going beyond that.

Like I said, I don't have access right now to the info. 
I do know that there have been many concerts done with less than the full compliment of 24 boxes per side (typically 18 or 19 MLA and a single MLA-D) with coverage out to 250 meters and drop off created at 300 meters to avoid noise complaints.

I will try to find the info that I have on the other coverage.  It was between 700' and 900' if I am remembering correctly although my memory is not what it used to be. :-)

Lee 
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Mac Kerr

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Re: "Multi cellular array" vs "Single Source array"
« Reply #46 on: July 23, 2016, 01:37:33 pm »

It depends on the freq involved.   Yes-in the top octave, the small horns (relative to the coverage pattern) will control the sound and keep the levels down for people out of the pattern, but as the freq goes down, they will lose pattern control and people will hear the multiple arrivals at close seats.

And as the frequency goes down the wavelength goes up, making the phase change critical point work for greater spacing between drivers.

Mac
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Ivan Beaver

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Re: "Multi cellular array" vs "Single Source array"
« Reply #47 on: July 23, 2016, 01:43:06 pm »

Like I said, I don't have access right now to the info. 
I do know that there have been many concerts done with less than the full compliment of 24 boxes per side (typically 18 or 19 MLA and a single MLA-D) with coverage out to 250 meters and drop off created at 300 meters to avoid noise complaints.

I will try to find the info that I have on the other coverage.  It was between 700' and 900' if I am remembering correctly although my memory is not what it used to be. :-)

Lee
It is the freq above 4K that is affected the most by air absorption.

Sure-there is plenty of sound below that.  But once you get above and actually MEASURE-you QUICKLY realize that there is a "problem".

I remember measuring my first stadium (BYU).

We had a mic at the far seats-about 700' in this case- and the response was rolling off on the top end.

So we boost a little at 10K.  Nothing happened.  We boosted some more-nothing happened.  I did not want to add more than 12dB of boost. The response was so low on the screen (as compared to the lower part of the response) we could not even see it.

This was using a TEF 20.

That night at the hotel I did some research on air absorption and realized there was NO amount of boosting that was going to get the HF response up at those seats.

That is when I said to my self-we need a "real" super tweeter.

And even then all we picked up was an octave.

But considering that is higher than most systems go anyway-I guess it is fine.

When you actually MEASURE at those distances-you realize how "tall the mountain" is you are looking at.

But casual listening will not tell you that.

Simply saying "I have highs out that far" does not mean anything unless you attach some REAL numbers to it.

Of course the "excuse" that many people like to use is "Well your brain is used to the HF rolling off at a distance-so it is OK">

OK-Let's "buy" that argument for a second.

BUT LOOK at the VIDEO screen!  They make it VERY LARGE so as to move you close to it.  In REALITY, a body on the screen would be very small and you could not see it at that distance.

So you would expect the sound to be "far away" as well.

But since they have moved the image closer to you-should not the sound be the same?

Should not the objective of any sound system be to provide the same experience for everybody? Or as close as we can?

That INCLUDES full freq response as best as possible-along with the same SPL.

YES- there will be exceptions and variances, that "should" be the goal.

I have a good number of "stories" that I can't tell (or maybe I could if I left off manufacturers names-I'm not sure on that one) about ACTUAL "like" experiences of line arrays and long distances vs a single source approach.

If people are interested in that-then I need to get moderators approval first.  But they would be interesting reading.

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Ivan Beaver
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Lee Buckalew

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Re: "Multi cellular array" vs "Single Source array"
« Reply #48 on: July 23, 2016, 01:53:46 pm »

I have a good number of "stories" that I can't tell (or maybe I could if I left off manufacturers names-I'm not sure on that one) about ACTUAL "like" experiences of line arrays and long distances vs a single source approach.

I am not talking about a line array, I am talking about MLA.

Lee
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Ivan Beaver

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Re: "Multi cellular array" vs "Single Source array"
« Reply #49 on: July 23, 2016, 02:08:57 pm »

I am not talking about a line array, I am talking about MLA.

Lee
Sorry-but I don't have any stories about any comparisons with MLA because I am not aware of any that have been done.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

ProSoundWeb Community

Re: "Multi cellular array" vs "Single Source array"
« Reply #49 on: July 23, 2016, 02:08:57 pm »


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