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Author Topic: When is it a line-array?  (Read 10927 times)

Peter Morris

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Re: When is it a line-array?
« Reply #10 on: July 28, 2014, 03:09:14 am »

I'm sure most of us have seen from one to three line-array "elements" mounted on a pole over a sub, or on a tripod stand as shown in this video.
http://www.youtube.com/watch?v=QZu8deHi6Ug
The DVA series are a very popular choice.
When there are only 2 or 3 "elements" stacked, will it actually perform as a line array?
If not, will it perform more like a point source speaker? How would we realistically expect a stack of 2 to perform?
I looked at the DVA spec sheet which includes the following specs:
Frequency Response [+/- 3dB]: 80 - 19.000 Hz
Directivity: 100x15 Single unit

At what range of the frequency response can we expect the 100X15 degree directivity? I wouldn't expect this directivity for the full frequency range of a single cabinet.

Do any of the professional audio societies have a published standard that defines what a "line-array" is?
I'm wondering how many "elements" you would need before the system actually begins to perform as a line-array.


Although the T4 is a line array box, two or three boxes is not a line array, its just an array with a narrow and adjustable vertical HF pattern.

In the case of the T4s, they have 2 / 3 box settings and work fine and you can add boxes until they behave as a real line array and the pattern control is extend to the low-mid frequencies. The longer the array the lower the frequency of the pattern control.

FWIW the T8s sound much better,  go much harder and integrate well with the T12s.
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TJ (Tom) Cornish

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Re: When is it a line-array?
« Reply #11 on: July 28, 2014, 07:22:28 am »

Hi TJ,
As described in this paper written by Meyer.
http://www.meyersound.com/support/papers/meyer_line_array.pdf
I ask, because even really long line arrays don't truly have what some folks claim - loss of only 3dB over double the distance distance compared to 6dB/double the distance of a "point source" - at least not intrinsically.  The advantage of a vertical array is that elements can be combined to throw more sound at the back of the coverage area and gradually less towards the front which to some degree equalizes the volume, however even really long arrays lose pattern control at low frequencies. This means that at some point you will lose the ability to produce equal tonality over distance if you are trying to chase equal volume, as the array only "works" down to a certain frequency, which is determined by the array length.

There are some ways around this, with caveats, as nothing is free.  JBL's 4886 system can be hung with the mid-sub 4883 elements in cardioid mode, which greatly improves LF pattern control, but using a different mechanism than line-array element superposition.

If your question is "Are 'dash' arrays useful and/or better than a traditional point source speaker?", that's a different thing, and the answer depends on what you're trying to do.  I have recently gotten to do some larger events with my 4886/4883 gear.  Saturday night we had 2 4883 over 7 4886, and it sounded really nice for our application from about 20' to 200'+.  Other than a couple Danley boxes like the Jericho and Genesis horns, I don't know of too many point sources that could do what we needed to do, especially with our hang weight of only 400lbs.

One application that is more questionable is for a permanent install.  It becomes harder to make the case for a relatively expensive "Swiss Army" system like most small format vertical arrays, when you can go to the catalog and buy the right point source boxes for the room and probably get better sound for less money.

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Ivan Beaver

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Re: When is it a line-array?
« Reply #12 on: July 28, 2014, 07:50:58 am »

I would argue that most people that talk about "line arrays" simply have no idea what makes up a line array-what the pattern control really means or have any idea how long (NOT the number of elements) they have to be to even begin to perform "line array magic" (ie 3dB/doubling of distance) or have a clue that even "point sources" can provide equal SPL (no losses) from the front seat to the back.

So why is the 3dB/doubling really important? And what happens to cause that "apparent" loss?  Hint- it is because of DESTRUCTIVE INTERFERENCE.  It does not make the far seats louder-the cancellation causes the near seats to be not as loud. 

But at a price of all sorts of "finger lobes" (you know-the things the marketing depts erase from the measured data) that can cause erratic response at different seats.

They look at the "pattern" number and assume it means that is the pattern over a wide range of freq. but yet if you look at the measured polar pattern (or do a little math yourself), you will see that often the stated pattern is only for the top octave or 2-not even getting down into the "important freq" for intelligibility. 

But that does not stop the marketing engines from churning out false information.
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Kevin McDonough

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Re: When is it a line-array?
« Reply #13 on: July 28, 2014, 08:52:08 am »

I would argue that most people that talk about "line arrays" simply have no idea what makes up a line array-what the pattern control really means or have any idea how long (NOT the number of elements) they have to be to even begin to perform "line array magic" (ie 3dB/doubling of distance) or have a clue that even "point sources" can provide equal SPL (no losses) from the front seat to the back.


hey

yeah what most people don't get is that there are two things happening at the same time to control the vertical pattern, one for the HF and one for the LF.

For the HF its simply controlled by the horn/waveguide as it would be for any other box. Yes they can be a bit fancy and complicatedly designed to turn the circular mouth of the HF driver into a rectangular exit running from the bottom to the top of the cab (and so join with the next cab) and try and keep a consistent path length etc, but at the end of the day, the waveguide's control of 5, 10 or 15 degrees is what allows you to aim the box.

however at the low/mid end, its the opposite. Especially with a reflex mounted driver, the coverage pattern will be the same as a point source. You stick a 12" driver in the front of a box and is doesn't matter whether its a "line array" box or a point source, its still a 12" driver on the front of a box and will output sound the same way. Its the vertical stacking of the boxes, and as Ivan says the constructive and destructive interference of the sound from these drivers when they're stacked within 1/4 wavenength of each other (which is largely what manufacturers aim for with line arrays), that begin to create pattern control just in the same way that a long line of subs also begins to aim the sound in an ever narrowing alley.

The extent to which this happens is down to the length of the line against the wavelength your talking about. So as the line gets longer it is able to maintain pattern control to a lower and lower set of frequencies. 

A small line array of only two or three boxes on a pole will have line array type pattern control, however it'll just be at relatively high frequency and will be increasingly more like a point source as you move down.

And note again, as Ivan says the length of the line overall, not the number of boxes. Whether its made up of twelve 6" boxes or six 12" boxes its the overall length that counts.  (well, technically the smaller boxes will have smaller drivers with slightly different characteristics and tonality than the bigger ones, and the individual drivers will beam differently and have their own individual pattern control, but BROADLY speaking its the length of the line overall).


So are short arrays worthwhile?  Yes, its another tool in the toolbox, they have good points and bad points.

The fact that you only have one line of boxes (each side) horizontally helps with interference between boxes. However you're stuck with a specific dispersion horizontally you can't just add a smaller number of narrow coverage boxes if you need narrow dispersion.

They have flyware built in (usually) so if you have points or truss to hang them from you can fairly simply. But if you don't they can be a little harder to groundstack if they don't come with a pole mount.

They will probably be made up of lots of smaller drivers at the polemount/two or three box size, and while they'll be more sensitive they'll handle less power and you may loose a lot of the low mid balls you'd get from just having a single 12" or 15" point source box, and so your subs may have to play much higher to meet them or you may need a dedicated low mid/upper bass box as well as subs.


However at the end of the day though, one of the main ways they will be different will be perception, and that unfortunately can be key.  While we would all like to make our decisions based on pure sound quality and what is the absolute best tool for the job sound wise, often there are many other factors.

And if you're gonna get a whole load of extra work because something that looks like a line array 'sounds' better to promoters, band members and venue owners then its hard to ignore that ROI.



k







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Brian Jojade

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Re: When is it a line-array?
« Reply #14 on: July 28, 2014, 11:23:58 am »

The very simple answer is, it's a line array when the marketing department deems it so.  Simple as that.
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Mark Cadwallader

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Re: When is it a line-array?
« Reply #15 on: July 28, 2014, 02:43:22 pm »

The very simple answer is, it's a line array when the marketing department deems it so.  Simple as that.

Oh, you mean a "lie arrary"!  Mark C.
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Scott Holtzman

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Re: When is it a line-array?
« Reply #16 on: July 28, 2014, 04:44:41 pm »

I am quite sure that the experts are tired of repeating this information but there is so much FUD concerning arrays that these conversations (especially with the same participants) have tremendous value to the community.

I touched on the Vue AL-4 and others mentioned compact and ultra-compact have a place.  Vue claims that they can alter the phase to each driver within a narrow range of frequencies and be able to control the pattern via software and physical alignment.

Is this an accurate claim?  If you went into one of these null zones would the energy still be there just canceled out?

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Kevin McDonough

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Re: When is it a line-array?
« Reply #17 on: July 28, 2014, 05:01:37 pm »

I am quite sure that the experts are tired of repeating this information but there is so much FUD concerning arrays that these conversations (especially with the same participants) have tremendous value to the community.

I touched on the Vue AL-4 and others mentioned compact and ultra-compact have a place.  Vue claims that they can alter the phase to each driver within a narrow range of frequencies and be able to control the pattern via software and physical alignment.

Is this an accurate claim?  If you went into one of these null zones would the energy still be there just canceled out?


yes, its accurate.  Just as I said above the basics of line array directionality are essentially the same as that of subs. More drivers radiating closely together in a line will, thanks to cancellations, will narrow the pattern. The longer the line the narrower the beam will become, and the lower it'll hold to.

And just like subs, by delaying cabinets you can make the waves meet in or out of phase at certain points and control the pattern.  Its very common to, for example, progressively delay the outer cabinets when you have a long line of subs across the front of the stage to counter the narrowing effect and widen the pattern again.

And essentially its the same process, a little harder to program/calculate/predict because of the smaller wavelengths and the aiming/j shape of the array and because you generally have more drivers and a much wider bandwidth to try and control, but essentially the same overall idea.


Martin and EAW are already doing it to great effect with MLA and Anya respectively. And their advantage is that you're not trying to do all the work, the trial and error of manually changing delay times and seeing what effect it has, change again and test, change again and test......  With their software you just tell it the coverage you want, where you want it to start and end and where/if you want 'holes' in the coverage to miss balconies and things, and then the software does all the hard work to calculate what processing all of the drivers need to get it done.


k



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Jay Barracato

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Re: When is it a line-array?
« Reply #18 on: July 28, 2014, 05:05:08 pm »



Is this an accurate claim?  If you went into one of these null zones would the energy still be there just canceled out?

I am not sure what you mean by this as it does not seem to tally with how energy is transferred in a wave form.

When two waves overlap with destructive interference at a particular point that doesn't cancel the energy that is being transferred through that point.
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Scott Holtzman

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Re: When is it a line-array?
« Reply #19 on: July 28, 2014, 05:52:41 pm »

I am not sure what you mean by this as it does not seem to tally with how energy is transferred in a wave form.

When two waves overlap with destructive interference at a particular point that doesn't cancel the energy that is being transferred through that point.

That is correct, basics if you connect two speakers out of phase and reproduce a sine wave and stand right in the deepest null with a SPL meter you will see the "energy" in that space still exists.

So even with the very granular pattern tuning these arrays are capable of it is not efficient as you need the original power and the power to cancel the unwanted coverage.

I just wanted to make sure I had the full picture.

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Scott AKA "Skyking" Holtzman
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Re: When is it a line-array?
« Reply #19 on: July 28, 2014, 05:52:41 pm »


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