| Line array vertical coverage specs? [message #412615] |
Thu, 05 March 2009 11:00  |
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 Jeff Hague
Messages: 522
Registered: January 2007
Location: Richmond, VA |
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Just out of curiosity - I have no use for a line array system any time soon but I cant get away from the ads...
How do they spec the vertical coverage of a line array cabinet? Most of them say somewhere between 5 and 20 degrees vertical coverage. Is that for an array of a certain number of elements or for a single element or is it just for the high component?
Many of the designs I see look like the lows are fairly standard front loaded bass reflex boxes - wouldnt they be essentially omni below the frequency where the wavelength equals the size of the cone?
"All those who believe in psycho kinesis, raise my hand." (Steven Wright)
http://www.richmondproaudio.com
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| Re: Line array vertical coverage specs? [message #412618 is a reply to message #412615 ] |
Thu, 05 March 2009 11:03  |
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 Duncan McLennan
Messages: 2237
Registered: July 2005
Location: London/Waterloo, Ontario |
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Generally it refers to the vertical dispersion of the high frequency section. It would be silly to spec vertical pattern control at lower frequencies, because that varies with the length and deployment of the array.
edit: typo
[Updated on: Thu, 05 March 2009 12:57]
Duncan McLennan
Waterloo & London, Ontario
'they may have an F3 of 23Hz, but what's the WAF?'
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| Re: Line array vertical coverage specs? [message #412665 is a reply to message #412615 ] |
Thu, 05 March 2009 12:32 |
Brad Weber
Messages: 2289
Registered: December 2005
Location: Marietta, GA |
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Are you addressing an actual line array or a curvilinear array? The latter are simply narrow vertical dispersion boxes intended to vertically array in order to provide the desired coverage, they are not actual line arrays. In those cases the vertical pattern stated is the nominal pattern for a box and each additional box adds approximately that much more to the overall vertical pattern of the array (often a bit less as there may be some overlap for smooth coverage). So with curvilinear arrays you can pretty much assume that two boxes is a certain vertical coverage, three boxes a different specific value, etc.
In comparison, a true line array may also have a nominal vertical pattern specified for each box but the overall array pattern is determined by both the number of boxes and the angles between the boxes. There is no direct correlation of the array coverage to the number of boxes, one has to account for the angles between boxes and how the boxes interact with one another. Typically, the manufacturers provide their own software for laying out line arrays and assessing the resulting coverage.
The entire theory of line array behavior is wavelength based. The way I view it is that there are two major components. First, two sources located within a 1/4 wavelength path difference will sum (it has nothing to do with the driver size), so if you keep the sources close enough together over all frequencies then they will sum at all frequencies. A quarter wavelength at 16kHz is 0.21", at 5kHz it is 0.68" and at 1kHz the spacing is 3.4", so you need to have the high frequency sources very close to get line array behavior. But at 100Hz a 1/4 wavelength is approximately 2.8' and it is fairly easy to get even large drivers within a 2.8' spacing of one another.
Duncan is still a little off in his response as the second factor is that the vertical pattern control of a line array starts to lose pattern control at lower frequencies and that frequency is related to the length of the array (the horizontal pattern control will usually drop off at low frequencies but due to other reasons and not as a result of the length of the line array). A true line array assumes an infinitely long source, which is impractical. However, at some point a line array gets short enough that it is no longer a line but starts to act more like a point source. Because of the longer wavelengths and fewer number of sources combining, that transition happens sooner at low frequencies and many shorter arrays actually act as a line array over only part of their operating range.
Brad Weber
muse Audio Video
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| Re: vertical coverage specs? [message #412881 is a reply to message #412682 ] |
Thu, 05 March 2009 20:04 |
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Mac Kerr
Messages: 9717
Registered: April 2004
Location: Westchester County, NY |
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| Jeff Hague wrote on Thu, 05 March 2009 12:00 |
Many of the designs I see look like the lows are fairly standard front loaded bass reflex boxes - wouldnt they be essentially omni below the frequency where the wavelength equals the size of the cone?
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| Jeff Hague wrote on Thu, 05 March 2009 13:54 |
| Brad Weber wrote on Thu, 05 March 2009 13:32 |
Are you addressing an actual line array or a curvilinear array?
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I dont think Im addressing either, per se. If you look at the latest edition of Live Sound Intl, for instance, they have a big spread on the latest medium format line arrays ("A rundown of line array modules with 8- and 10-inch woofers") and they list specs for each one. They all list horizontal by vertical coverage as 120 by 8, 100 by 15, etc. but they dont specifically say whether that peertains to a single "module" or an entire array (of any type) or whether it pertains to a particular frequency band or not. It leads you to believe that the module itself has that coverage pattern through its entire passband which seems inplausible since many of them employ pretty traditional front loaded drivers for their lows. I know that traditional ground stacked cabinets report their coverage pattern based typically on the HF horn and not the mid or low units but isnt dispersion control what an array is all about?
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How is that spec different than every other speaker that gives a horizontal and vertical dispersion angle without specifying the frequency range? A UPA-1P says it is 100ºx40º, but that is not only just the horn, it isn't even the full range the horn covers. That is true with almost all speakers.
Some of the more restrained LA builders don't specify a single box vertical coverage, they say the vertical coverage depends on the array size and geometry. Which is absolutely true.
Mac
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| Re: Line array vertical coverage specs? [message #413876 is a reply to message #412615 ] |
Mon, 09 March 2009 13:02 |
SteveKirby
Messages: 2106
Registered: October 2007
Location: Santa Cruz |
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This may be a gross oversimplification, or a misunderstanding on my part, but my take on this is that at higher frequencies the 1/4 wavelength or coupling is within the height of the box and thus needs to be controlled vertically to prevent interference with adjacent boxes. While at lower frequencies, the coupling is between boxes. Thus you have the front loaded drivers with no apparent pattern control devices. The pattern control being derived from coupling with other boxes in the line. The longer the line the lower the frequency this coupling creates vertical pattern control over.
So the manufacturers list a vertical pattern spec for the range that couples within the cabinet so that folks know what range of angles they can splay the boxes at without undue interference (which obviously still happens to some extent) or significant gaps. If someone hung a line with a huge gap in between adjacent cabinets (say they put a sub or two in the middle of the hang) then the lower frequencies wouldn't couple correctly and the pattern control would be affected in those ranges.
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