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Old 16th May 2008, 02:34 PM   #1
xlr8 is offline xlr8  United States
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Post Line array with coaxial drivers

Hello all,

I'm new here, but decided to go ahead and join because the internet brings me here to answer most of my questions about audio in general. Thanks to everyone for allowing my fist post to possibly be a stupid question.

My current system includes:

Antique sound lab wave line pre
2 DBX 234 active crossovers
Kenwood (sorry, don't know what model) 6 channel main amp
Maggie MG 3as
Crown XLS 402
2 JL Audio 12" w3 subs in sealed enclosure, compound push-pull arrangement.

If you can't tell, the system is 4-way and sounds pretty decent overall. It is an amalgomation of cheap parts and components that local Hi-Fi dealer reccomended, since I'm on a fairly tight budget.

On a side note, I have to say that tri-amping an old set of maggies will really bring them to life. My set had been passed around a few times before I got my hands on them, but I doubt any of those other owners EVER heard them sing like they do now! I conidered several options for subs and settled on the JL's out of convienience. The sound of these subs in a compound push-pull arrangement is nothing less than stunning.

I now find myself considering whether or not to let go of the aging maggies (they need too much work to keep them alive) and start over fresh. I had the pleasure of auditioning a set of line arrays that an acquaintance built, and was blown over backwards by their sound. His house sounded like a dance hall. What shocked me even more was that he said he used some of the cheapest drivers he could find, I believe MCM is the manufacturer. I never would have imagined that a handfull of cheapo drivers could sound like that! He used 12 4" drivers and 12 of these tiny tweeters that looked like car audio stuff. I'm wondering if coaxial drivers might be appropriate for a line array design. Any help you guys could provide would be greatly appreciated. I've considered some Hi-Vi Research car coaxial drivers for my new project. I know i'll give up control over the tweeters if I do this, but do you guys think it'd really matter? I welcome all opinions, criticisms and advice you guys could give.

Thanks in advance!
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Old 16th May 2008, 02:48 PM   #2
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Hi,

By using coax speakers you will have a separation of the tweeters. This is not good because you end up with comb filtering issues.

Quote from the PE site:

"Comb Filtering: An artifact seen in multi-driver systems that is the result of constructive and destructive interference from multiple point sources. The addition or subtraction of multiple sources will vary with location relative to the speaker. Comb filtering becomes more of a concern at higher frequencies due to the shorter wavelengths involved. Most often used when talking about line arrays where spacing between tweeters can be problematic."
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Old 16th May 2008, 09:17 PM   #3
xlr8 is offline xlr8  United States
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Thak you. This is exatly why I joined this morning. I've yet to see a coax/line array system in my quest. I guess that should've clued me in, yet at the same time I wonder how different designs for things mght work, never knowing who has tried what and been succesful. It's good to know that there is a place for my questons, as well as answers I can take to the bank and I thank you all.

My first thought was to possibly go with a line of Silver Flute tweeters and a line of discontinued Focal 5.25's from Zalytron. I've seen designs that use just one ribbon tweeter and have also considered donating the ribbons from my maggies to the cause, but am usure if this would even be a possibility. I'm definately open to suggestions here. I want to stay reletively cheap, but not as cheap as what I saw at my friends place. I can only magine that the results would be better if I use components that are a hair better than his.
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Old 16th May 2008, 09:26 PM   #4
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If I had more time I would look for the white paper by Dr Jim Griifin. In the meantime why don't you mosey over here and see if you can dig up some ideas. Dr Griffin is a member here so have a look see at his posts. If you can't find something there then post again or google his white paper on line arrays.

http://www.diyaudio.com/forums/searc...der=descending
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Old 16th May 2008, 10:59 PM   #5
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An alternative would be a focused array, which will circumvent the combing issues. They have their own issues -smaller sweet spot than a line array etc., but they do allow things a line array doesn't.
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Old 16th May 2008, 11:58 PM   #6
graaf is offline graaf  Poland
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Quote:
Originally posted by Cal Weldon
Hi,
This is not good because you end up with comb filtering issues.
Quote:
Toole spoke of comb filtering, and has deduced that it is an artifact of measurement, not an audible problem in normal listening.
see: http://www.linkwitzlab.com/Acoustics...ll%20Rooms.doc

human hearing is insensitive to narrow notches, an established fact in psychoacoustics

I don't know, any comments?
Floyd Toole seems to be quite authoritative source
who am I to argue?

best,
graaf
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Old 17th May 2008, 10:10 AM   #7
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True enough as far as it goes (at least assuming you're on-axis). What it doesn't cover is the severe attenuation of the high frequencies that is also a consequence, which need massive Eq to bring them ~flat once again.

See the FR curves of this project, using 2in TB drivers to see what I mean. http://www.partsexpress.com/projects.../Kuze3201.html You'll get pretty rough HF out of them, even when Eq'd approximately flat.
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Old 17th May 2008, 03:01 PM   #8
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Quote:
Originally posted by xlr8
nd have also considered donating the ribbons from my maggies to the cause, but am usure if this would even be a possibility.
They should be extractable. The ribbons in maggies would make an ideal support tweeter for a line array. Being as long as it is, you would have no gaps to cause comb filtering.

dave
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Old 17th May 2008, 03:05 PM   #9
onform is offline onform  England
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Has anyone ever built and tested a line array using point source drivers like KEF makes?? this puts the tweeter at the center of the mid bass driver giving them natural time alignment, you might say they are the closest thing to a single full range driver which always sounded like a great idea to me..

my two pence..
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Old 17th May 2008, 03:07 PM   #10
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Quote:
Originally posted by onform
Has anyone ever built and tested a line array using point source drivers like KEF makes??
How high any driver can go in a line array is determined by its centre-to-centre spacing. In any coax the tweeter spacing will be the same as the midbass, so the tweeter can go no higher than the midbass (basically making it useless)

dave
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