Line Array Puzzle

paulslhac

Member
Hi Everyone,
Its a bit of a basic, sillly question, but where I work, we have a Renkus Heinz CF101LA Modular Point Source Array as our permanently installed FOH. Its arrangement is (from top module to bottom) 3x High/Mid's, 2x Subs.

Pictures of the same array online show the subs on TOP of the array.
My question is, why do people put the subs on top of a line array sometimes? And why might we have the subs on the bottom?
Cheers!
 
I would say it depends on the high frequency coverage required. The subs are omni directional while the highs are directional. If you have near field coverage, then the subs should be on top and the highs lower. I would put the subs on top if they woould interfere with the high end coverage.
 
From a mechanical standpoint, subs are also more standard in shape and size, and tend to be heavier and larger. Makes them simpler to rig boxes together when on top, and makes the center-of-gravity of a given array less off-kilter. For those reasons, it's more practical to choose between ground-stacking and flying subs at the top of an array than it does to fly them at the bottom of an array.
 
To add to Mike's points, the a CF101LA box weighs 47.5 lbs. while a companion CF15S subwoofer weighs 114 lbs., almost 2-1/2 times as much as the full range box. The CF15S is also quite a bit physically larger. Thus in terms of rigging it is generally easier and more stable to have any subs located at the top of the array.

Another factor here is that the CF101LA is not really a line array, it is a curvilinear array or what R-H calls a modular point source array. Each full range box provides 15 degrees of vertical coverage and you vary the number of boxe in the array to get the desired total vertical coverage up to four boxes for a 60 degree vertical pattern. The CF101LA boxes are thus designed to be tight packed with a fixed angle between full range boxes. On the other hand, the subwoofers being omnidirectional have no angle between them or the adjacent full range box. Two vertical boxes with three angled boxes below would typically be easier to rig and more stable.

Put those together and there are usually a number of good reasons to locate the subwoofers at the top of the arrays while there are only two reasons I can think of for rigging the subwoofers at the bottom of the arrays. One possible reason would be if they were trying to get the full range boxes located as high as possible with a limited trim height while the other reason might be to get the subwoofers far enough away from a reflecting surface above to avoid potential boundary cancellation issues.
 
In my opinion, the best reason, and others have stated this, is that the subs will usually dictate where the tops end up. So really the subs need to go wherever puts the top boxes in the best coverage pattern for the audience.
 

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