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Old 19th January 2002, 06:16 AM   #1
Won is offline Won
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Default Line Arrays

What do people think of line arrays? They seem to be a pretty good and simple way of using many relatively inexpensive drivers to build a decent speaker. I haven't noticed much information on building them, however. Is it as simple as just stacking multiple drivers on top of each other?

Also, about the wiring. Usually, multiple drivers are wired in some series/parallel combination that puts them near the 4-8 ohm range, but there's been at least one disucssion hereabouts regarding low (insert more o's in there...) impedence loads. I think someone wanted to parallel 32 driver or something? What about speakers with very high impedences? Like 50-100 ohms? The amplifier would need a bigger voltage swing, but this is better for class-AB amps, anyway. I would imagine that most amplifiers drive larger loads more stably and with less distortion.

Regards, Won
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Old 19th January 2002, 07:10 AM   #2
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Line source speakers are capable of excellent sound reproduction. How well an array of smaller speakers works depends on the frequency you're trying to reproduce. At low frequencies relative to the spacing of the individual drivers, multiple drivers work well. Unfortunately, at higher frequencies, the wavefront no longer combines; it breaks into lobes and nulls.
The Loooooow Impedance thread interested me, as I like ribbon drivers, which are (with the exception of the Magneplanar ribbon) so low in impedance that they are generally driven with transformers. Since I use the Magneplanars, it's not strictly necessary, but I wanted to fiddle with the idea anyway. If nothing else, the very extremity of the concept attracts me. At the moment, however, I'm tied up trying to get a Mini-Aleph finished, and after that, I'd like to get to the...um...well, the "Clamor" circuit. You know...<i>that</i> one.
On the other end of the spectrum, higher impedance loads are indeed easier to drive. That's an interesting idea also, but not quite interesting enough to force its way into my queue of things I want to play with. As a passing hint, note that tubes just love to swing voltage...something like a 6AS7 or 6C33 in the right circuit would be happy as a clam if you were to give it 30-50 ohms to play with.

Grey
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Old 19th January 2002, 07:34 AM   #3
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Clamor, Clamor..... I'm also designing/building a version of the Clamor, Clamor circuit... oops shouldnt have said that, now everyone will probably bug me too oh well it might give Grey a rest for a while...
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Old 19th January 2002, 10:20 AM   #4
JohnR is offline JohnR  Australia
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User YA posted his line array spreadsheet on the Madisound board a few weeks back, it's quite instructive, his page is at

http://briefcase.yahoo.com/bc/yavuzaksan

(look under Share).

My understanding is that an array needs to be at least 70% of the floor-ceiling height to be considered a true line source. I think the height is needed so that, in theory anyway, the floor and ceiling reflections cause the array to mimic an "infinite" line source.

That's all a bit much for me, I'll be experimenting with a "short array" ie four drivers on a side. Suboptimal but at least it's somewhat affordable! The spreadsheet above indicates that four drivers is not too bad in terms of comb filtering, any more and you have to go the full length. GR Research has the new BG Neo8 ribbons for $60 (I think) apiece. He also has a line array kit, in case you were interested in that...

Well, sorry for the long-winded post, hope some of this is useful!

JohnR
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Old 19th January 2002, 01:59 PM   #5
ucla88 is offline ucla88  Tahiti
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Quote:
GR Research has the new BG Neo8 ribbons for $60 (I think) apiece
hey, do you have a link to this? there webpage doesn't seem to mention this.
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Old 19th January 2002, 04:21 PM   #6
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A line source has to be longer/taller than, I think, a half-wavelength at the lowest frequency you intend to reproduce. This isn't a problem at 20kHz, but gets trickier at lower frequencies. Reflections come in handy.
My subs and mid/tweeter arrays are a whisker over 7' tall (eight foot ceiling except for where it shelves down to 7'4" at the front of the room). The woofer panels are 6', but are more properly considered planar speakers, so I can't claim to be line source from top to bottom. One of these days, I'm going to try a thing or two to see if I can sneak past that limitation, but it'll have to wait.
The Bohlender-Graebener RD-75 makes a very nice line source mid range unit, but don't try to run it all the way out to 20kHz as it gets quite soft sounding on the top. It's good down to about 200Hz on the bottom.

Grey
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Old 19th January 2002, 05:18 PM   #7
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Default speaking of arrays...

Won, there is a friend of mine who is currently designing a DIY line array pair. His name is Rick Craig, and he is a respected member of the DIY community (and has a good reputation on the Madisound list). I am told that he is near completion, and he recently posted a message to that list here saying so. If you can wait a short while, he will release his cabinet and crossover design along with his bill of materials for anyone to build.

One of the primary factors of this project was the cost. I believe Rick says you can build them for $700/pr (excl. cabinets).

Grey : Rick is using ribbons in his design. If you are a fan then you might want to take a serious look at this.
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Old 19th January 2002, 09:41 PM   #8
Won is offline Won
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Grey --

It did occur to me that having a high-impedence load would mean that it would be more favorable to tube gear. Is it high enough for an OTL tube amp? The only OTL tube amps I have seen have been headphone amps.

-Won
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Old 20th January 2002, 12:09 AM   #9
JohnR is offline JohnR  Australia
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ucla88, I don't think Danny has anything on his web page. He posted about it on harmonicdiscord.com, but that site is down now :-(. I think parts express was going to sell it as well. The data sheet is on bgcorp.com. They have a peak at 12 kHz, according to Danny this goes away if you have eight of them, I am not sure however if some eq is needed to bring the top end up.

I am planning to use four of the Neo8s per side instead of a full array ($$!). I will also try four midranges I got from Madisound next to them, not sure yet if I can make it work as a two-way. Anyway I haven't got the ribbons yet, I need to sell off some stuff on EBay first (sort of like the rotating equipment merry-go-round :-()

Won, OTL amps do like higher impedance loads, up to a point that is when output is limited by supply voltage rather than current delivery. But a 16 or 32 ohm load is certainly more favorable to an OTL. There are commercial OTLs by atmasphere and transcendentsound for quite a while, and there are a whole slew of newer ones that also cost a pretty penny (Joule, Graaf, I forget who else). There are also many schematics on the net, if you are interested let me know and I'll try and list as many as I can. I plan to wire my mid and ribbon arrays as 16 ohm loads and build low power OTLs for them.

JohnR
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Old 20th January 2002, 12:11 AM   #10
JohnR is offline JohnR  Australia
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I forgot about Rick's design. I wish he would publish some of the details already! He keeps putting out these teasers :-)
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