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Old 18th April 2010, 12:24 PM   #1
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Default Dipole line-array idea

I'm thinking of a 2-way dipole line-array using the B&G RD75 ribbon and a stack of woofers of some kind. There well be no baffle, just nude drivers suspended from the ceiling or a tall frame.

I've never seen or heard the RD75, so any comments would be nice before I go and order them...

As I understand, the RD75 is dipole / open backed. It should be possible to run it well below 1 kHz even as dipole, even thought it will roll off somewhat.

With XO below 1 kHz, using 10" woofers and still keep the dipole peak above XO is possible, and with enough drivers there should be plenty of bass as well. The RD 75 is approx 1,9 meters tall. Eight 10" woofers would match well in terms of total height of the speaker.

Okay, what do you think if this?
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Old 18th April 2010, 12:57 PM   #2
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A sketch of the idea:

Click the image to open in full size.
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Old 18th April 2010, 02:35 PM   #3
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There are a couple of people on the HTGuide DIY forum who've been using something similar for several years now.

HTGuide Forum - BG RD75 for line array
HTGuide Forum - New Home for the BG Ribbons - Part 27

Try a search on that forum, there are probably other threads that might be relevant.
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Old 18th April 2010, 02:49 PM   #4
chasw98 is offline chasw98  United States
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As Saurav said, go check out HTguide. I am one of the guys who is currently running 12 Peerless 6 12" woofers, B&G Neo8's, and B&G Neo3's for a 3 way dipole line array. It stands 7 feet tall by ~24 inches wide. Custom electronic crossover with crossover points at 40 Hz (to subs), 800 Hz (woofer to mid), 4 KHz (Mid to tweet). Lots and lots of dynamic range, very clear, and very precise in the reproduction of music.

Chuck
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Old 18th April 2010, 06:51 PM   #5
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Nice projects, but not designed for Constant Directivity with those very wide baffles. My idea is to run the drivers without baffle. Havent found anyone doing that with the RD75.
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Last edited by StigErik; 18th April 2010 at 06:53 PM.
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Old 18th April 2010, 08:08 PM   #6
NiklasJ is offline NiklasJ  Sweden
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This diy ribbon might be an interesting alternative to the rd75?
Byggbeskrivning för den neodymiumbestyckade band
(sorry, article in Swedish but you can perhaps translate with google)

Used in these speakers, not baffle-less but said to be very, very good.
Click the image to open in full size.
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Old 19th April 2010, 05:34 AM   #7
NiklasJ is offline NiklasJ  Sweden
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I've thought about someting similar myself, but a little less tall design with those diy ribbons mentioned above. I'm not sure you really need something 2m tall to make an efficient linesource? But you seem to be used to so much more spl capacity so you might need it for shear cone area...
Coupled with tapped horn subs or your giant 21" h-baffles for the lowest octave I'd think this would make a killer system I think.
For 10" mids I've thougt about Beymas 10g40 and 10mw/Nd (more open rear structure might be good) or Eminence BASSLITE CH2010 (hempcone, small neo magnet)
Suppose one of the Seas excel 10" woofers might be useful too but I hav'nt tried simuating those, low sensitivity IIRC...
Best regards,
Niklas
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Old 19th April 2010, 08:03 AM   #8
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Being Norwegian, I can read swedish perfectly....

Making my own ribbon is a little bit out of scope right now, but its interesting to give it a try sometimes. Being a bit lazy, I think I'll stay with off the shelf drivers to begin with... therefore the RD75.

I'm thinking good paper woofers for this, Excels are just too damn expensive. Very open rear structure is necessary, ruling out the otherwise good Beyma's. Something with small magnets (Neodymium) and very open basket is fine.
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Old 19th April 2010, 01:39 PM   #9
el`Ol is offline el`Ol  Germany
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This one has a tiny magnet:
http://www.ciare.com/pdf/catalogo/CW250.PDF
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Old 20th April 2010, 02:39 AM   #10
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Quote:
Originally Posted by StigErik View Post
I'm thinking good paper woofers for this, Excels are just too damn expensive. Very open rear structure is necessary, ruling out the otherwise good Beyma's. Something with small magnets (Neodymium) and very open basket is fine.
An RD75 no baffle line array is a back burner idea I've been kicking around. From the HTGuide threads the cross could be 500Hz or lower. So I'm unsure there's a hard requirement for a small magnet/very open back---with most woofers the problem for the back wave is the spider and the magnet's kind of incidental. A woofer with a vented pole piece might be a better choice. mige0's observations on low Rms seem particularly apropos here due to the magnetostat integration and low power per woofer in a line array, but low Rms, low Fs drivers are hard to find. They're eight inches, but the Beyma 8BR40 and Peerless 830667 and 830869 are ones I've had in mind. Haven't actually spotted any ten inchers that look as attractive as the 830667 (I'd cross LR6 so I'm not too worried about the diffraction dip at 900Hz). There are some interesting twelves, but that starts to get a bit bigger than I'd like for the frequencies I have the impression the RD75 would be happiest crossing at.

Quote:
Originally Posted by el`Ol View Post
The rule of thumb I've been going by is Fs on the lowest woofer should be about where one's willing to accept roll off in the bass. Which, for me, means 30Hz or so. Though I've a hunch Stig Erik plans to use subs to handle the very low bass, in which case there's more flexibility on the woofer Fs.
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