Let's Design a Pro PA Line Array

[Randy L]

If you were to design a portable line array speaker for PA/DJ use, along the lines of the Bose PAS sticks, which drivers would you use and how would you design & build the cabinets?

I'm thinking a non-powered version able to handle a good 500 watts RMS, get nice and loud (high spl rating per driver) but very clean sounding.

Knowing a sub is needed, how would you design the thin & tall "stick" so it secures to the bass/sub cabinet? Is there some sort of twistlock insert to "snap" the stick onto the sub?

I doubt any true full range drivers would work due to the high power ratings for PA use, so I'm thinking an array of six-eight 6" (or so) extended range drivers topped with one or two quality pro super tweeters to cover the very high frequencies might be the way to go. Of course, this would necessitate the designing and building of a passive crossover network with x-over freq dependant on the selections of drivers and tweeters.

Trying the keep the stick's appearance as narrow as possible, the cabinet would be just a bit wider than the drivers used. With this in minds, how would you attach the speaker grill (I'm thinking extruded metal like PE sells here for a full faced grill)?

Other than wood, what other materials might be used? Remember that it must be well built to withstand the rigors of load ins & outs, and "gigging"

[Paul O]

You will need something that looks like this IMO... http://www.slsloudspeakers.com/content/view/264/107/
preferrably processed with DSP and powered with a seperate amp channel for each mid and high section. Subs can be reflex or horn loaded and should be positioned for best room coverage.. which most likely won't be directly under the arrays in most cases.

[Randy L]

Paul,
I've seen those designs and I've always been confused about the placement of the HF drivers, being on the side. I thought the mids might be preventing the even horizontal dispersion of the HF freq's. I've always read that the best driver alignment was vertical for the best dispersion/polar pattern, or is this old school thinking?

Last night, I too began to think that the best design for the subs might be a pair of 15" subs side-by-side, at the center of the "stage" area for the best coverage. The arrays would be standing alone to the sides. If the subs could be hidden, can you imagine the look on people's faces wondering how you're getting bass from a couple thin sticks.

[Randy L]

Forgot to add...in respect to Parts Express, let's use PE products.

Considering Paul's suggestion, what do y'all think about the Dayton planar tweeter in the array? Using 5 would achieve the 400 watts RMS goal. Maybe using 6-8 per cabinet might be better?

http://www.parts-express.com/pe/show...number=275-085

Only issue I have is that placing the planars or other HF driver beside the mids makes for a cabinet that is pretty wide...possibly 11" wide.

[Randy L]

Just got a brainstorm. How about making the cabinets deeper (maintains the thin appearance up front) to allow recessing the mids, then mount the Planars in FRONT of the mids?

[meep]

keep in mind that the bose arrays cross into the subs fairly early... it's less sub and more a "bass cab". Don't recall off-hand, it's been a few years, but I'd guess 150Hz or maybe a touch higher? 160-180?

I love the idea of this project btw...

M

[AMC]

A side note I guess, but generally when speaking of line array in pro sound, you are talking about Stack-able cabs that produce a line array, some might be confused.

One thought on a system like this might be to use a open baffle design(or at least open back), crossed over very high, maybe 400-500hz, to dual bass modules. This would reduce weight, and make it more flexible as far as drivers in the array go.

What exactly is your purpose for this? (location, size, music...)

Also, I would avoid the 'super tweeter'. they almost always sound harsh, are hard to control, and there just is not that much music up there. A good 1.? driver with a good lens would do everything you should need. Just put it at the top with a horn matched to the array width.

[Randy L]

^^ very good point about the classification of "line array"

My intent is to see if we could collectively come up with a great design for a "stick" to be used for live sound or sound reinforcement use (DJ, etc.)

Emulating the Bose PAS systems which have the numerous drivers in a vertical line array design, I think we could come up with one that looks almost as nice (slim profile & very portable), and hopefully sound exceptional and LOUD.

[wg_ski]

While you might be able to come up with something that sounds pretty good, I'd question just how *loud* you're going to get a stack of itty bitty drivers that aren't supposed to be very loud to begin with. Those Bose systems don't go very loud and you're up against the same laws of physics. How long do you think the PT2's will last? 20 seconds, IYL?

I would be thinking more along the lines of 8"/1", in something like 36" sections that could be stacked/bolted together. Two or three high for a small dance hall, go higher outdoors (but the rigging is up to you and your lawyers). Put the 8" line side by side with the HF drivers - one LF to one HF. The horn flares may need some custom machining to make it appear like one big long one that goes end to end. It may take a few iterations to get it right, but plastic horns are cheap. If the BFM cabs can do this with PIEZOs, it could certainly be done with D220's, etc.

[AMC]

While you might be able to come up with something that sounds pretty good, I'd question just how *loud* you're going to get a stack of itty bitty drivers that aren't supposed to be very loud to begin with. .

I would agree.

I think you/we should state a goal, here might be an example...

Base modules, less the 6 ft3, under 50lbs

Towers, 48 inches tall, 8 inches wide, shoot for under 50lbs.

whole system should be able to produce 130db with no more then 1000watts TOTAL power. (think 2 QSC GX3 amps)

and about 50 - 15,000 Hz range?

I'll work something out and get back to ya. Any other parameters we should set?

[AMC]

Heres an idea.

each side...
6-8 Eminence Alphalite 6A-CBMR 6" Neo Sealed Back Midrange
Mate that with a 1 inch driver and horn of suitable width.

under it, a 15 in scoop run up to 500Hz (here come the scoop haters)

The sealed back mid ranges would make the box design almost irrelevant, and it could be made very lite. The scoop should be able to deliver up to 500Hz without to much trouble, although it is far from ideal. Consider a basslite 15 for this. (C2515?) or maybe a deltalite 15. Avoid the LF drivers as their midrange tends to be less then fantastic.

The regular alphalite 6's would be great, but then the box is more important, and heavy, and they are not as efficient.


Opine away...

[billfitzmaurice]

Heres an idea.

each side...
6-8 Eminence Alphalite 6A-CBMR 6" Neo Sealed Back Midrange
Mate that with a 1 inch driver and horn of suitable width.

under it, a 15 in scoop run up to 500Hz (here come the scoop haters)

The sealed back mid ranges would make the box design almost irrelevant, and it could be made very lite. The scoop should be able to deliver up to 500Hz without to much trouble, although it is far from ideal. Consider a basslite 15 for this. (C2515?) or maybe a deltalite 15. Avoid the LF drivers as their midrange tends to be less then fantastic.

The regular alphalite 6's would be great, but then the box is more important, and heavy, and they are not as efficient.


Opine away...

Crossing from the sub to the top at 500 Hz is poor practice, as is using scoops, which are reviled for good reason. And placing the subs under the tops is wrong in so many ways. Stick with standard Alpha/Beta 6s or 8s for a 100 to 150 hz crossover and cluster the subs. There's also no advantage to 1" throat compression drivers or planars, KISS with a vertical array of piezos.

[Paul O]

I'm old enough to remember when scoops were cool and very popular, but there are so many much more capable designs now without the compromises.. so why bother.

Back to the project..

It seems the column speaker is making a resurgence, several big name companies are now marketing new install products based on the idea including Tannoy Qflex and the JBL CBT series. This JBL design puts the tweeters in a row in front of the mid column..
http://www.jblpro.com/catalog/genera...x?FId=89&MId=2

[Randy L]

Bill,

I'm tending to agree with you that the 500hz rolloff of those Alpha-6's may prove to be a bit too high. On your suggestion of the piezo's, I've used them quite a bit in various designs and feel they sound a bit too harsh. Is there any type of passive filtering to smooth them out? I've even read that some have lightly stuffed the mouths of the piezo's with some mild fabric or foam to tame them.

On the above remarks about the itty-bitty drivers...YES...I agree. I just didn't want to limit the imagination by saying the drivers had to be minimum size "X".

My thinking is a grouping of 8 quality pro driver in the 6" size, crossed over at around 150-200hz to the bass bins. I kinda like the idea of leaving the "sticks" alone to each side of the stage (not rock concert levels, but more a small to meduim sized venue) and clustering the bass cabs...hidden if possible.

[Paul O]

Emulating the Bose PAS systems which have the numerous drivers in a vertical line array design, I think we could come up with one that looks almost as nice (slim profile & very portable), and hopefully sound exceptional and LOUD.

There's a project in the showcase http://www.parts-express.com//projec...oject=Kuze3201 that's almost exactly what you describe but it won't go very loud and just like the PAS needs an additional bass module.

How long do you think the PT2's will last? 20 seconds, IYL?

Are they really that fragile? How robust would a stack of 8 be wired series/parallel for 4ohms? I was considering those for a project like this but wondered if they could produce the output to match 8 Dayton PA-165's.

[Randy L]

I'm quite intrigued by the Dayton Planar tweeter and wonder how it might actually sound in a PA application.
http://www.parts-express.com/pe/psho...85&ctab=2#Tabs

Taking cues from the JBL's CBT line, what about placing 7 of them in FRONT of 8 mid drivers? The planars are 3-1/2 wide so they wouldn't hide/block too much of the mids. Otherwise, like Bill suggested, maybe a stack of piezo's in front of the mids? While piezo's (by design) don't need crossovers, I found they do sound better when crossed over at around 2.5khz.

[Paul O]

I'm quite intrigued by the Dayton Planar tweeter and wonder how it might actually sound in a PA application.
http://www.parts-express.com/pe/psho...85&ctab=2#Tabs.

Yeah me too.

Otherwise, like Bill suggested, maybe a stack of piezo's in front of the mids? While piezo's (by design) don't need crossovers, I found they do sound better when crossed over at around 2.5khz.

And there's another rub... one of the advantages of a proper line array is wide polar response, but to maintain that over the whole spectrum crossover frequencies have to be below the point where drivers begin to beam excessively, and that means a 2khz crossover for the tweets at the most.

[Randy L]

What about this Selenium 6" woofer?
http://www.parts-express.com/pe/show...number=264-422
I like the RMS rating, though I'm not too confident in the 9khz response. According to the freq. response curve, it looks like it becomes "unstable" above 2khz. Cost ain't too bad neither.

[billfitzmaurice]

On your suggestion of the piezo's, I've used them quite a bit in various designs and feel they sound a bit too harsh.

Then you haven't used them in a line array. They aren't very flat, but it's pro-sound, where DSP isn't an option, it's a necessity, so flat response is moot.

[wg_ski]

PT2's...

Are they really that fragile? How robust would a stack of 8 be wired series/parallel for 4ohms? I was considering those for a project like this but wondered if they could produce the output to match 8 Dayton PA-165's.

They're not especially fragile - any more than any other home stereo tweeter. Which experience has shown time and again can't be used for any serious PA app. People get the idea that a "tweeter" will do just as well because it can handle the same 40 watts as a standard 1" compression driver. But at 10dB less sensitivity, you ask it to do 10X the work, and that's where you run into trouble. I know of the argument that "there isn't much up there" because of the typical power distribution of full range music. But you can't rely on that where a speaker may be subject to full power peaks in the vocal range, or feedback, or clipping....