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Old 10th May 2005, 10:29 PM   #1
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Default WR125ST quadpole?

I'm thinking of doing a sealed design, 30L cabs with MTM on the front and MM on the rear. Four WR125ST's in parallel, XO @ 5kHz, to an Usher Tweeter (LR2, or LR2 woofer/BW1 tweeter).

The bass will roll off naturally at about 90 Hz, with a pair of subs to fill in the bottom.

What do you think? Has anyone heard a bipole MTM speaker?
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Old 10th May 2005, 11:07 PM   #2
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sounds expensive if nothing else.
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Old 11th May 2005, 01:03 AM   #3
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Originally posted by Josephjcole
sounds expensive if nothing else.
Joe
I don't know about that. Comparable in price to a lot of three-way designs, and considerably less expensive than the Jordan JX53 Linear Array.

I was inspired by this thread and Planet10's bipole mania:

New Reference Speakers with Full/Wide-Range Driver

I wonder if SurfSun&Sound ever found a system that suited his spec, 90-4kHz with no crossovers? It makes sense to me to avoid a crossover in the middle of the male vocal range, which is what most three-way systems do.

Four 4-1/2" cones are equal to a couple of six-inchers per side, and you need to move some air at low frequencies to get better realism.
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Old 11th May 2005, 01:18 AM   #4
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Yeah, sorry didn't mean to cut your idea down. I'm sure having four drivers would make it more dynamic, and raise it's power handling. I guess I'm just a little bit of a cheap skate. They certainly are nice drivers though. I guess it would depend on your needs. Personally I would think two per channel would do quite well, wheter it be MTM or bipole, but my room is fairly small, and I don't crank it up all that often.
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Old 11th May 2005, 01:58 AM   #5
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Quote:
Originally posted by Josephjcole
Personally I would think two per channel would do quite well, wheter it be MTM or bipole, but my room is fairly small, and I don't crank it up all that often.
Joe
I do like to get jiggy wit it sometimes. But maybe you're right... I should try it with two drivers per cabinet. I could always add the other two later.

I have a pair of the CSS drivers running full range in 7L ported cabs right now. They definitely don't cut it unless they're close to a wall, and there are no nearby walls in my main system. Maybe two drivers will be enough. Thanks for the feedback.
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Old 11th May 2005, 03:51 AM   #6
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audiobomber, I have been thinking about exactly what SurfSun&Sound proposed in 2002 and it is fortuitous that the WR125s came along. Thanks for providing that link as I had not been aware of it. I have come to the conclusion, though, that bipole and dipole configurations create more problems than they solve. This link explains the most of the problems. http://www.smr-home-theatre.org/Type...ker-Types.html One of the fallacies in loudspeaker design, IMHO, is the old pulsating sphere idea. This method would be good if each sphere was an instrurment that was being reproduced. Unfortunately this is not the way music is recorded. It is more accurate to think of reproducing music to replicate an inverse microphone. A mic picks up sound at a point in space. The sound it picks up is 70% reflected, these are the spacial clues, and 30% direct. In order to maintain a reasonable facimile of the sound it would be optimal if a speaker produced 70% of is sound directly and 30% reflected in order to approximate the original event. This concept rules out the bi/dipole . This logic may be flawed and I look forward to any discussion of this.
While Tim of Alegria presented his TL design using a pair of WR125STs in an effort to gain bass extention, I agree with you that it would be better to use a sealed design and utilise a sub for below 80hz extention. I dont think you need a large cabinet for a pair of STs though. I started a thread in the loudspeaker forum about using an aperiodic design for a pair of STs and came to the conclusion that 7L is enough for this purpose.
In Tim's TL thread Jim Griffin chimed in about uneven response caused by comb effects due to the proximity of the 2 drivers. The centers of the drivers are 10.8 cm apart that would correspond to appproximately 3300hz. at which point comb effects above this frequency would start to set in. This is a much lower XO point than has previously been considered for the WR125 but then again most of the designs have been for a single driver. I just wanted to point out that 2 STs next to each other add another complication to the mix. Crossing over at 3300hz, or thereabouts would call for a more robust tweeter such as the Morels which also have excellent dispersion and would mate with the dispersion of the STs pretty well at 3300hz. In an MTM, though you'd be separating the STs even farther apart than 10.8 cm and thus lower even further the freq at which comb filtering sets in. Mounting above , on baffle, or even on top of the cabinet, at the acoustic center, with a top mounted Morel, would solve this problem, and in the case of the top mount, would create a time aligned design.
Feel free to critique any of the ideas I've proposed. I might be wrong about all of them!
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Old 11th May 2005, 07:42 AM   #7
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Quote:
Originally posted by konut
This link explains the most of the problems. http://www.smr-home-theatre.org/Type...ker-Types.html
A basic shallow description, but he doesn't even touch on the problems, when a problem is an advantage -- in the end he says to paraphrase. "all speakers are a compromise, you have to listen to them and decide"

The MTM/MM idea is one that i've played with to get more grunt out of a small speaker. I'm not a big fan of MTMs in general so i didn't take it too far.

The WR125 is so good and so cheap, this one is a good idea. You do need to get a tweeter that can reach down fairly low.

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Old 11th May 2005, 05:58 PM   #8
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The only bipoles I've heard are the big Mirages and they sounded good to me. How they'd sound in my room though, is an open question.

I'm going to have to give this project some more thought. It's obviously more complicated than it seemed last night. A few thoughts though: Wouldn't comb filtering be reduced because the speakers fire in the opposite direction? And don't forget, I'd roll of the the rear drivers at the XO frequency, so not all the highs would be bouncing around. I also wonder if maybe the reduced vertical directivity of the MTM would help with comb filtering from the rear drivers.

I see what Jim is saying about the front mounted midranges interfering with each other. A lower XO would help, but it kind of screws up the intent of crossing over high. At this point it's looking like this thread doesn't belong in the Full-Range forum.

Right now I'm listening to my Frankenspeaker. A WRS125 in a 7L cabinet plopped on top of my speakers, crossed over to a woofer at 1.5kHz with an Usher tweeter rolled off with a .68uF cap and 3-ohm resistor. Comb filtering is definitely causing some blurring in the highs, but this thing makes music.
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Old 11th May 2005, 06:51 PM   #9
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Quote:
Originally posted by audiobomber
I'm going to have to give this project some more thought. It's obviously more complicated than it seemed last night. A few thoughts though: Wouldn't comb filtering be reduced because the speakers fire in the opposite direction? And don't forget, I'd roll of the the rear drivers at the XO frequency, so not all the highs would be bouncing around. I also wonder if maybe the reduced vertical directivity of the MTM would help with comb filtering from the rear drivers.
I don't think that you need to worry about comb filtering on the back drivers. On the front drivers, standard MTM rules apply... with the WR125 an XO above about 4k is probably pushing it.

For a true bipole the back drivers should be run FR, if you are going to roll them off, then at the baffle-step (making a 2.5 eay probably makes the most sense.

And then if we consider the number of people who have reported perfectly satisfying results flying in the face of the rules (ie Morse dual FE167) one could just say... go for it. simply roll off the tweeter with a cap.

Another alternative i came up with for using 4 drivers in a single box, was to build an EPI Tower inspired speaker with a driver on each face of a square prism.

dave
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Old 11th May 2005, 11:57 PM   #10
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Tim Forman, was kind enough to let me listen to a pair of WR125STs in a TMM combination. Maybe they would have sounded better bilpole, I don't know, but they certainy sounded like music to me. Better than the single WR125ST. So while I'm sure comb filtering can be a problem I didn't notice any major problems with Tim's speakers, quite impressive really.
I guess I would think the optimal would be bipole and rolling in the tweeter pretty high with a single cap and resistor. This I guess would be dependent on how far away from walls you could place it. A smallish sealed enclosure should keep the drivers from over excursion, that way you could keep the WR125STs going with out a crossover. Of course then you would need a sub. Lots of options I guess.
just my 2cents
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