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Old 7th July 2005, 07:42 PM   #1
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Default Speaker design help/168E Sigma & woofer

I thought I'd get some opinions/thoughts from the experts. I've been planning to build a set of speakers for some time, but need a little help on the design end of things. I'm hoping to roll with this project in near future, though it will take some time to do.

What I plan to do is use a pair of 168E Sigmas running full-range but rolling off the bottom end, say around 200-250hz or so with a simple cap. Then, bringing in a 12" woofer on the bottom on each side. Right now, I'm thinking one of the better Eminence pro sound drivers. Basically, I'll have two cabinets on each side, with the 168 cab sitting on top of the woofer cab, possibly spiked to it. I may incorporate a supertweeter for just a that last touch of air, as I have a pair not in use.

My main question is, how to house the 168E Sigmas? Should I do something sealed? A small folded pipe? Ported? Any thoughts would be appreciated. And if you have any specifics as to the enclosure size, that would be appreciated. My main goal is to make sure the sound is nice, tight, and full bodied.

Then there are the woofer cabs. My intial thought is just to do a ported cab. But is that the best option here? I'm thinking of the Eminence Magnums, which will work in a smaller cab than most. Again, could try a folded pipe, MLTL, etc. I'll have some size to work with, but can't go huge.

One more question, how to amplify the system? I have been using 300Bs, but have recently aquired and interesting gainclone in the form of an Audio Zone 40 watt prototype. It's really quite a nice amp, (very smooth, wonderful imaging, full sound) but is that enough juice for both drivers? Or should I use a plate amp for the subs? The 12" drivers look to be about 95db and the Fostex is 94.5 (as I recall).

Any thoughts would be greatly appreciated! Cheers!
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Old 7th July 2005, 08:42 PM   #2
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Sensible way: sealed box for the Sigmas, transmission-line for the subs. Don't couple them together though, you'll just get loads of unwanted vibration, which is Not A Good Thing. Plate amps for the twin subs, use your 300B or gainclone for the Sigmas. Add the super-tweeters if you feel like it.

That's the sensible[ish] way. Naturally, I wouldn't do this. Oh no. I'd try something a little... different. (Hope you're sitting down? Yes? Good. Got a brandy? No? I suggest you get one before proceeding.)

Welcome back. It all depends on if you can afford 4 sub-drivers and plate-amps -the ones you've picked would be ideal. However, we're getting ahead of ourselves, so, first up, the FE168ESigma.

FE168ESigma in a straight MLTL (with some BSC), or possibly Terry Cain's Bigger Is Better box (I still can't figure out exactly why it works -the model looks terrible, yet they measure beautifully in room, and sound it too). Use your 300B (PP or SET by the way?) or gainclone to drive these. The bottom end is now going to get the mother of all support.

Why did I say four drivers and amps? Simple. Fancy a pair of dipolar open baffle subwoofers? (Grin). Very compact, and frighteningly effective, if the drivers and plate-amps are up to it. Celestion made some briefly a few years back, and these were the best subs ever made in my view. This isn't about quantity (though depending on the drivers and amps, they'll get you down to about 5Hz) but quality. Like all open baffles, they simply don't excite room-modes as readily as conventional box types, giving much cleaner bass. Two pairs of drivers, one pair per channel. Push-push mounted, magnets touching or mechanically coupled togther. Stunning subs like nothing else.

Oh -and avoid spikes. I've been campaigning against these things for a while -it's just habit, and a bad one -you create an open acoustic cavity under your speaker: the worst possible place for one. Cover the base of the speaker in Blu-Tak or some such product, and stick it to a nice piece of marble or a concrete paving-slab covered with a cheap iron-on veneer. You'd never think about spikes again.

Mad enough for you? Hope so.
God Save The Whale
Scott
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Old 7th July 2005, 08:53 PM   #3
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Certainly if you've got the amps/preamps I'ld go active crossover as well. However I wouldn't run the 168s open, I'ld put them in sealed enclosures and cross them where ever you see fit. I cann't speak for the 168s, but my 108s sounded much better with a crossover to keep them from struggling to reproduce the bass. Much more dynamic and they can know got quite loud with out ever sounding strained. If I had it to do again I would also go with open baffle bass as I am now trying to figure out how to deal with all the room issues I've got.
Joe
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Old 7th July 2005, 09:10 PM   #4
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Default Thanks for the thoughts folks!!

Any additional info on the open baffle subs? I've seen iterations here and there, but would like to know just what you are referring to.

I tend to agree with Joe on the MLTL vs. sealed. One other option is to go open baffle with the sigma driver, though I may raise the crossover point just a hair in that case. I do have to consider how much room I have. It would work the best to stack the two pieces, or have them share a baffle.

I'll be back in the morning, hopefully can look into this a touch more throughout the day.

Thanks!

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Old 7th July 2005, 10:06 PM   #5
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Here's a review of the Celestions. I seem to remember Noel Keywood of Hifi World magazine and World Audio design produced a good crossover for these beasts, often used with the Quad ESL63 electrostatic, which gives some idea of how good they were / had to be. My variation would be to flip one driver around, so it works in push-push configuration though.

http://stereophile.com/loudspeakerreviews/892/

I agree that IB mounting is probably superior to MLTL -unless you go for a rare sealed line which eats the rear-wave completely. I suggested this way, mostly because I prefer not to cross subs over that high. Just personal preference really. I wouldn't normally try the FE168ESigma on an open baffle if it's being run full-range, but with it being crossed over at a high level, as you seem to wish to do, with bass / sub drivers in support, it becomes a viable option, nor would you need to worry [as] much about the baffle-width. I would still avoid stacking speakers if possible: that said, those Celestion subs were frequently used with ESL63s sitting on top of them with superb results, so nothing's impossible. I would still advise you to avoid spikes though; there are other, far better ways of decoupling cabinets from each other.

Cheers
Scott
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Old 8th July 2005, 12:59 AM   #6
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Quote:
Why did I say four drivers and amps? Simple. Fancy a pair of dipolar open baffle subwoofers?
That is exactly what I m working on now. Four high efficiency 15" JBL 2226 clones by Dayton (from Parts Express) and a pair of Lowther PM2C, PM2A, or DX4 drivers on an open baffle. Two amps and a 4th order active crossover and the calculated response looks very nice. No real deep bass but ~100 dB efficient down to 50 Hz and 6dB down at about 30 Hz. That is what the calculations say anyway.

I looked at different enclosure designs and while they gave more bass extension they started to become huge boxes. This looks very easy to build and configure in my room. If it does not work it will be easy to drag out for the trash. The back loaded horn design went to the back burner.
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Old 8th July 2005, 07:36 AM   #7
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Sounds a good plan to me Martin; do keep us updated as to progress -I'd be interested in hearing about your results and thoughts. -6db at 30Hz sounds pretty good to me!
I still love transmission-lines, especially the straight MLTL and TQWT varients, but as you'll have guessed, I've increasingly been thinking about open-baffle and dipolar types recently. Modest size, simplicity and room interaction (or lack thereof). I haven't started on any subs yet, but I'm in the process of trying out the main panels from Siegfried Linkwitz's Phoenix design (minus the subs). OK, not using full-range drivers, but they're simple, active panels and the specified drivers are excellent quality. My greatest problem at the moment is that my current room isn't really large enough for open-baffle designs to perform optimally; hence my using more 'conventional' (ha!) boxed types at present like a TQWT or MLTL.
All the best
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Old 8th July 2005, 01:23 PM   #8
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MJK

Can I ask which drivers you're looking at? That sounds like excellent response. I assume a higher Q driver would be preferred, but the 2226 has a pretty low Q.

If you'd be willing, I'd love to see your plans for this.

Thanks!
Layne
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Old 8th July 2005, 03:07 PM   #9
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Can I add my name to that too, if we're not either asking trade secrets or jumping the gun here Martin -interesting that we were working toward the same sort of thing!
All the Best
Scott
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Old 8th July 2005, 04:48 PM   #10
MJK is offline MJK  United States
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The woofers I plan to use are Dayton 15" high efficiency drivers :

http://www.partsexpress.com/pe/pshow...=295-080&DID=7

The SPL for 1 watt input at 1 m distance is 97 dB and the Qts is 0.37. The manufacturer's specs are very accurate and consistent based on my measurements of the four units I have at home. These are very similar to the more expensive JBL 2226 which I was strongly considering. I would rather apply boost to a magnetically overdamped driver then have a ringing impulse response due to a high Qts driver.

My preliminary plan is to use two per side in a 20" wide by 40" tall baffle crossed over to one of my lowther drivers at approximately 200 Hz. I am probably going to buy a Marchand XM6 crossover which is 4th order and has adjustable frequency and gain for the high and low pass signals. The Lowther driver will be at ear level and the two woofers stacked below. I am still finalizing the baffle size trading boost against size.

I have a new OB MathCad worksheet that factors in the driver and baffle geometry and includes the crossover slopes and the floor reflection. The response looks very good with something like a +/- 2 dB gentle roll from 50 Hz to 1 kHz. I have examined the calulated response on axis at different distances and also the polar response and by keeping the crossover below 200 hz things look very promising.

Should be a simple build so hopefully I will have results by the fall.
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