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Author Topic: When is it a line-array?  (Read 10913 times)

Peter Morris

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Re: When is it a line-array?
« Reply #30 on: July 29, 2014, 08:32:55 am »

It does not steer at all.  It covers the entire area that is available based upon the array inter cabinet angles.  From there the top and bottom apertures, as they call it, are affected by either being available to be heard or by being canceled.  Same goes for exclusion zones.  This is all budgeted into the processing ahead of time so that there is enough DSP processing available to allow for the required cancellation or addition.  There is no steering occurring.  When steering is done every time you change where a beam is pointed you change the frequency response adjacent to that beam.  From a physics standpoint what MLA does is very different from beam steering.

Lee

Hi Lee,

I may have used the term "steer" too loosely and we maybe talking about the same thing - as you know, for a given coverage area you calculate the inter box angles and FIR coefficients for each of drivers and up loaded them to the boxes.... about 15 minutes of number crunching on an i7.   Without rehanging the array you can change the coverage area slightly by recalculating new FIR coefficients and up loading them again...

« Last Edit: July 29, 2014, 08:39:52 am by Peter Morris »
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Peter Morris

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Re: When is it a line-array?
« Reply #31 on: July 29, 2014, 08:33:40 am »

Kevin,

I agree with Lee, its not a beam steered array, its exactly as Lee has described above.

It was not done by trial and error but complex mathematics. It appears to use a fuzzy logic type of optimization programme to manipulate the complex vectors that describe the phase, amplitude and frequency response of each speaker; maximizing their summation on the listening plan by determining the required EQ, delay, amplitude of each speaker within the array, taking into account the different angles and height of each speaker. 

When I saw what Ambrose had done I was in awe!

Peter           
« Last Edit: July 29, 2014, 09:39:28 am by Peter Morris »
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Lee Buckalew

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Re: When is it a line-array?
« Reply #32 on: July 29, 2014, 11:42:56 am »

Hi Lee,

I may have used the term "steer" too loosely and we maybe talking about the same thing - as you know, for a given coverage area you calculate the inter box angles and FIR coefficients for each of drivers and up loaded them to the boxes.... about 15 minutes of number crunching on an i7.   Without rehanging the array you can change the coverage area slightly by recalculating new FIR coefficients and up loading them again...

Peter,
I am not trying to be picky but precise.
To me, understanding these types of differences goes a long toward helping me to understand the complex interactions that are going on.

I too am in awe of what Ambrose understands in his brain and then translates into filter sets, algorithms, and computer interfaces.

Lee
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Brandon Wright

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Re: When is it a line-array?
« Reply #33 on: July 29, 2014, 12:14:54 pm »

It does not steer at all.  It covers the entire area that is available based upon the array inter cabinet angles.  From there the top and bottom apertures, as they call it, are affected by either being available to be heard or by being canceled.  Same goes for exclusion zones.  This is all budgeted into the processing ahead of time so that there is enough DSP processing available to allow for the required cancellation or addition.  There is no steering occurring.  When steering is done every time you change where a beam is pointed you change the frequency response adjacent to that beam.  From a physics standpoint what MLA does is very different from beam steering.

Lee

And how exactly do you think Anya achieves its "beam steering? ???
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Lee Buckalew

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Re: When is it a line-array?
« Reply #34 on: July 29, 2014, 10:36:41 pm »

And how exactly do you think Anya achieves its "beam steering? ???

Precisely that, through beam steering.  It is a flat hung array that only steers.  It lacks phase coherence and demonstrates this because it does not hold up well over distance or in wind.  It is very flexible in its ability to adjust to varying coverage needs from a single hang, more flexible than similar Renkus systems.  Anya is a very useful tool but Anya and MLA are significantly different approaches to the physics of audio reproduction.

Forgive me if I am seeming short.  This week is very long as I am working with the marvelous Brad Ricks and George Georgallis from JBL tuning a large stadium install.  Long tired days seem to make my answers more clipped than I intend.

Lee
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Peter Morris

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Re: When is it a line-array?
« Reply #35 on: July 30, 2014, 07:48:43 pm »

Peter,
I am not trying to be picky but precise.
To me, understanding these types of differences goes a long toward helping me to understand the complex interactions that are going on.

I too am in awe of what Ambrose understands in his brain and then translates into filter sets, algorithms, and computer interfaces.

Lee
.... its actually a pleasure to talk to some who has an understanding  of what these guys have done  :)
« Last Edit: August 07, 2014, 11:00:45 pm by Peter Morris »
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Tom Danley

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Re: When is it a line-array?
« Reply #36 on: August 01, 2014, 01:59:45 pm »


I'm wondering how many "elements" you would need before the system actually begins to perform as a line-array.

Hi All
I had intended to reply sooner but we have had a death in the family which has occupied much of my time.                 
Acoustically speaking, a line source is “a single source” which is acoustically “very large” in one dimension and small in the other.   To be an acoustic line source (reaching the theoretical -3 dB per doubling of distance) it is assumed to be straight and infinitely long but like optics, “infinity long” isn’t from here to the edge of the universe and back etc  but rather, infinity here (where the behavior essentially stops changing as a function of length) is normally about 40 or 50 wavelengths or longer.   
Using the word “line array” is a way around the acoustic requirement for that acoustical condition of a continuous source.     Here one instead has an array made of individual radiations where each source radiates with it’s individual directivity and as a result creates some overall directivity via Huygens wave front construction but as Ivan mentions the radiation going up and down and elsewhere while present is ignored. 
This interference (not coherent addition) also means it takes many more sources to reach a given SPL at a distance as much of the energy is lost in the self canceling process and also much energy projected outside the desired direction.

The problem of changing behavior vs frequency when the line length is less than infinitely long is reduced by bending the array which acoustically makes it an astigmatic point source instead and so if one measures one of these directly on axis, the spl essentially rarely falls off at the vaunted “half as fast” as a point source.   While we think in terms of frequency response, time enters into the picture musically as not everything is a continuous sine wave and a single impulse fed to such a system, produces a train of arrivals reflecting the different path length to each source from the listener position. This condition can be corrected with DSP but only in one location by applying appropriate delays etc.

 As Ivan mentioned, the array of individual sources also produce “finger lobes” as the configuration of individual radiations still produces an interference pattern, exhibited by a pattern of lobes and nulls above and below the aimed axis and comb filtering.  When one makes a high resolution measurement or plays pink noise and move around you can see and hear all that..     
It is the self interference or interference pattern and changing directivity vs frequency that cause the line arrays to be strongly affected by a crosswind and to have a very limited useable working distance, which humorously is the exact opposite of the marketing which asserts they have “longer throw” than a point source.  Many of the stadium systems using real point sources “throw” and sound fine at 700 or 800 feet or more.

The “point source” term itself is another name that is normally used incorrectly in loudspeaker marketing and sales, a point source (acoustically speaking) radiates from a single point in space (and ideally time if you’re a fan of Heysers work) and so even a simple 15 and a horn is no longer a real or acoustic point source but an array of two point interfering sources.     
One can add individual sources and have them add coherently but the sources must be less than about ¼ wavelength apart at the highest frequency of interest (as one finds with multiple subwoofers).
The up side of the tiny line array is that they are mostly not a line array acoustically, they have less self interference and so one can achieve a more constant sound spectrum vs location more like a point source.   
Many have observed that the smaller the number of boxes one uses, generally the better it sounds, one can have a “perfect box” but when you stack 16 of them up, what do you have then?   
 
At the far opposite end of this effect, a real acoustic point source will sound essentially the same at any distance (minus some hf loss due to air absorption, only the spl falls with distance) and lacking an interference pattern, also sounds essentially the same even in a strong cross wind or walking the pattern with pink noise.     
If one also has constant directivity and a high front to back sound ratio (easy to do with a single large horn),  if one can place the source at the right height, then one can have a near constant SPL and spectrum from right under the source to the farthest point AND radiate much less energy in the wrong directions than an array which is great when you have a room or stadium to contend with.  The down sides for MFR’s is this is very hard to achieve acoustically and it requires far less cabinets, drivers, amplifiers and dsp for a given audience SPL.

In some of the stadiums where real constant directivity point sources are used in, one finds the SPL varies only + - 3 or 4 dB from under the system out to 700 or 800 feet and subjectively it sounds the same in every seat and produces only one arrival in time which is a big plus musically speaking.
One can steer either type of an array as well, before the line source craze and before I found a way to have drivers combine coherently over a wide bandwidth, I had a patent on the approach which is  popular now for making a steerable array’s.  Examine the Fig’s for this old expired patent.

https://www.google.com/patents/US4845759?dq=tom+danley&hl=en&sa=X&ei=nsvbU5X8JJGqyASyy4LIAg&sqi=2&pjf=1&ved=0CDgQ6AEwBA

The down side here is the more one angles the radiation relative to the source locations, the greater the sound energy projected outside of the desired pattern becomes and it remains difficult to make all the sources combine coherently and not radiate as individual sources..
Best,
Tom Danley
Danley Sound Labs
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Tommy Peel

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Re: When is it a line-array?
« Reply #37 on: August 01, 2014, 02:23:10 pm »



Hi All
...
Best,
Tom Danley
Danley Sound Labs

Great information as always. That's one of the easiest to understand descriptions of line arrays vs point source I've read.

My condolences for the loss in your family.

Have a great weekend,
Tommy



Sent from my Moto X (XT1053) using Tapatalk

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Ivan Beaver

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Re: When is it a line-array?
« Reply #38 on: August 04, 2014, 09:09:42 pm »

Here is an interesting article that puts a lot of things in perspective

http://education.lenardaudio.com/en/07_horns_3.html
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

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Re: When is it a line-array?
« Reply #38 on: August 04, 2014, 09:09:42 pm »


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