poor man's line array

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bigugly

Well-known member
Joined
Jun 27, 2004
Messages
220
Location
Burbank, CA.
I started designing a DIY line array to replace my brothers aging Peavey PA. I want to load a ribbon tweeter in it but I am having trouble finding one that is has a high enough sensitivity and also won't break the bank. Currently the plans are to fit it with two of these planar tweeters. http://www.parts-express.com/pe/showdetl.cfm?Partnumber=275-085 The woofers are Eminence Delta 10A. Here are some of my initial sketches.


Anyone have any experience with this? Help me Obi-Wan Kenobi, you're my only hope. ;D

thanks,
James
 
I was wondering why you are considering using a ribbon tweeter. Horn high frequency drivers are about 4x more efficient for the same input power. Care should be used in selecting the corner frequencies at which they rolloff into the bass system to avoid high levels of throat distortion but this is relatively easy to do using the manufacturer provided specs. Also, you will want to use a "natural" rolloff rate of 12db per octave, but that would be true independent of the type of speakers being used.

Also, I noticed that your system is a horizontal array. This may cause some problems at higher frequencies if both cabinets have a tweeter in them. You will get interference effects in the horizontal plane, which is not a desirable phenomenon. That is why makers of line arrays stack them vertically. That will produce the widest horizontal coverage and put less wasted power in the vertical direction.

A good source of all types of speakers for construction projects is http://www.madisound.com.
 
Thanks for the reply burdij. The reason for the ribbon tweeters is the naturally narrow vertical, yet wide horizontal dispersion pattern. Also my system is a vertical array. If I were to use a regular constant directivity, exponential, or radial horn in this cabinet I would have to have what would normally be its horizontal axis rotated 90 degrees. This would undoubtedly cause interference in the high frequency vertical plane as the lobes from the cabinets adjacent to one another overlap to a great degree. This sketch shows how I plan to rig these speakers.

 
> line array

A Line Array has infinite horizontal dispersion; or pretty-much. This is a way to avoid the radical changes of dispersion found in simple cones and horns.

In practice, a "line array" for PA will be wide in bass and worked up until horizontal dispersion narrows past 90 degrees; or have semi-horns to hold 60 degrees from mid-bass to crossover.

A Ten Inch cone (8" working diaphragm) will be about 60 degrees at 1,700Hz. This is not out of line with the claimed 2KHz of your proposed ribbon (which I doubt will survive high-level club work).

But your 21"-wide duplex will focus to 50 deg by 650Hz. And will have very erratic off-axis lobing from 500Hz all the way up. In particular it will have severe side-lobes at 940Hz, where the two cone-centers are one wavelength apart, and reinforce each other in the typical direction of the microphones.

In typical clubs/dives, only slight horizontal directionality is needed; the audience sits all around the stage; but huge vertical directivity is useful to control reverberation. And it is a sour cliche to be directional 350Hz up (15" cone on box) and all boom/mud omnidirectivity in the 150-350Hz range.

BTW: that wide-pair scheme was designed for home theater, to "project" the midrange of the center (dialog) track to the sweet spot (the owner) without wall-spray. In a club, this is just wrong: folks on-line get too-strong mids, folks everywhere else get weak sliced-up mids.

You want your array over 4 feet tall, but as narrow as possible.

However for high acoustic efficiency you want 16 square feet of radiator.

There's no 100% way to resolve the two goals.

Well-designed line arrays often use 6" cones up to horn crossover. However a good loud strong Six is expensive and you need a lot of them. The low price of commodity gitar speakers is attractive.

Set your Tens just one-wide, and as many up as you can fit in the Econoline. A 1*8 stack of Tens is a very impressive sound-thrower in a low room, and pretty effective outdoors. It does get beamy above 1KHz-2KHz.

The range above 1KHz is where line-arrays are really hard to do well at low cost. In a project for a very long cathedral I've sketched four Eights. The back wall is only 20 degrees wide from the speaker location, so this will smear 10KHz all across the back; however it may be quite dull at the ends of the front pew and at the podium.

I have not tried these, and I hate piezos, but at a buck each, you can array three to each Ten and get your shrillness cheap.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=272-306

If you can cover <200Hz some other way, a one-wide tall-stack of Eminence Alpha-6A will give very smooth sound across the 200Hz-3KHz range, keeping most of your "voice" in one bandpass rather than sliced by crossovers. Past there, an array of cheap piezos is as good as anything after the second beer.

Pyle Pro PDMR5 or Dayton PK165 are much cheaper alternatives, and will sizzle pretty good over most of the place, leaving less for piezo fill.

You don't want my advice. I spent a lot of my youth exploring "better" PA systems. Did some good stuff. Also had a lot of push-back from performers who did not really want something different than what they grew up on. Or, by tuning for performer's on-stage expectation, gave the audience bad sound. And always a lot of work building and refining, re-building after road accidents. Adopters re-jiggering my careful plans all out of shape. Hundreds of hours of work with not a whole lot to show for it. I do think the better factories, like Peavey, DO give you excellent value, with a wide range of "how good can you afford?" Once in a while I hear one that is jaw-dropping, 98% as fine as my RCA drivers on hand-carved wood horns, ready-built and warranteed.

Get another Peavey, Mackie, JBL system. Especially this year, pawn-shops and other sources must be flush with gear idled by the economic downturn, like the Porsche for-sale on the lawn across the street.
 
We use ribbon speakers at the venue where i work. They work and sound absolutely great at high concert level spl. So it is definately possible to achieve. Max spl for the ribbon drivers we use are about 145dB.

http://www.alconsaudio.com/site/technology.html
http://www.alconsaudio.com/site/q_series.html

So its definately possible to do, but probably not at low cost...?
/J

 
Hi, I'm an L.Acoustics operator. Line array is definitely difficult to do. Most of the PA you can find are not eal "line array" and suffer of huge phase problems.
Mr Christian Heil (designer of the V-DOSC, K1, KUDO...) has defined a rule for WST (Wave Sculture Tecnology): any of the transducers must be at more than half lenght of the lower frequency they provide to the other transducerdelivering this frequency.
More clearly if your Highs tranducer cuts at 2Khz the Mid transducer must not be farer than 8,5cm (I'm talking there about the acoustic center of the transducers ). Two narrow High drivers must not be farer than 1cm !!! Mr Heil found the solution to get this with his high horn ( and deposed a patent on it). Here is why there's not a lot of real "line arrays" IMO. Most of the PA builders are not following this rule, and thats why most of the line arrays are not that good IMO.

PS: Line arrays are a huge fashion in PA... The use (I would say abuse) of line arrays most of the time is a complete non-sense (even if that make me feed my children  ;D ). I already put line arrays for a 300 people audience which is a complete non-sence as the benefit of the line array was only above 13kHz (vertical lenght of the line divided by 4 determine the lower frequency wave length where you've got line array benefit) ...

PS2: I must verify some of the WST rules but I'm quite sure I do remember well...
 
Thanks for all the info everyone. Once again PRR comes through with the goods. I will certainly defer to your superior experience. I am currently building 4 of these @ 18" wide. http://www.billfitzmaurice.com/T39.html These will take care of everything from 200Hz on down. Jonkan, those are some serious drivers. Unfortunately they are probably out of my price range. lolo-m, where can I find more info about Mr. Heil and WST?

Anyway,I offer everyone here my revised design.


These are set up for an 8" mid/woofer and that cheap planar I mentioned in the OP.(I'm still looking for a better alternative) The cabinets are 16" wide, 11" high, and 11.5" deep. Is there any recommended reading I should get on this subject? Thanks again.

James
 
bigugly said:
lolo-m, where can I find more info about Mr. Heil and WST?

Here are 2 links about L.Acoustic (the best PA in the world IMO  ;D, and at the same time the more expensive too  :'( ):
http://www.l-acoustics.com/

All the technical informations are on this page (WST and the DOSC throat) :
http://www.l-acoustics.com/anglais/retdgb.htm

L.acoustic build the first working Line Array in the 90's... As his PA systems prooved their superiority and became impossible to do without, the others tried to find other solutions to acheive the same results with more or less happyness...

Adamson is working really well too. I won't name the ones which are not working IMO  ;).

PS: the ribbon tweeter is the best choice to do a good line array, but haven't got enough of sensitivity for huge PA systems...
 

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