Trying to build dipole sub - a la Celestion 6000

>I like the effects I heard with the Celestion but I'm not confident I can reproduce the same results by just mocking up the design. I rather play it safe and go with a tested design.

You can do better. For instance mounting one woofer magnet in and the other magnet out results in a ~15dB reduction in even order harmonic distortion.

If you lack the gear (calibrated measurement microphone, USB interface microphone preamp, software like ARTA) capabilities or motivation (take what you built to an open parking lot and make ground plane measurements) to measure and adjust I'd build a well cooked Linkwitz design, probably one of the H-frame options (Seas drivers per Orion 3.4 with purportedly better large signal performance) since you'll avoid a cavity resonance near your passband. Even with the gear I'd be inclined to share Siegfried Linkwitz's or John Krevosky's driver choices because they've taken the opportunity to listen to and measure a number of drivers' performance in open baffle installations.

>I am concern about the ringing of the woofers as it will be box-less design. It will have to be something that provides servo/braking to keep the bass notes true.

I don't know what your technical concern is here.

People (the Carver Amazing dipole comes to mind) like to use high-Q woofers to compensate for the 6dB/octave dipole roll-off although drivers are minimum-phase devices so where you have flat amplitude you can't have time domain problems.

With a box you get inductance from the air spring in the box in parallel with the suspension compliance which increases both the resonant frequency and Q. Without you just have the driver Thiele-Small parameters and needn't have higher Q.

For sub-woofers the metal cone breakup is so far out of the driver's passband it doesn't matter.

Aerodynamic noises are a bigger issue since you no longer have a box to attenuate them. Pole or cone vents are a fine idea. Voice coil tinsel leads can make noise too but that's at a low enough level that although audible with sine wave test signals it will be masked with music.

Maybe I was a bit harsh with that oxymoron statement. The point was that deep bass (20 Hz) may be impractical with dipoles and that moderate bass (40 Hz) is possible but requires double the drivers as a conventional monopole. The other concern with dipole subs is the excursion of the drivers.

I also made a mistake. Meniscus Audio, not Madisound, offers custom baffles/boxes.

In your particular case, a crossover around 173 Hz is a bit of a problem. If you look at the Rythmik/GR amps, they are limited to 120 Hz. Contact Rythmik whether this is defeatable. Then, you're looking at your Behringer as a crossover again. That's also a fairly high crossover for summed left/right output.

Personally, the concept of the drivers facing each other seems counter-intuitive for a dipole. The effect would be much the same as a boxed speaker. Ya, I can see how it bring more control to high Q drivers and reduce that boomy
sound. The "Direct Servo", along with suitably designed drivers, ameliorates that condition to some degree.

My local dealer here in Scottsdale has a pair of these subs
(the complete 6000 system) on eBay right now. You have a week to watch the auction.
These might go high in the eBay "Frenzy", but since you probably don't want the SL600s, you can flip them if you win the auction..
My dealer is Esoteric Audio, (garyhjerpe on eBay).

04-22-12: Ngjockey
>Personally, the concept of the drivers facing each other seems counter-intuitive for a dipole.

There aren't enough pictures to see what's going on with the Celeston, although opposing drivers are fairly common.

W-frames let you get more displacement out of a given enclosure (spouse approved, or in Monte's case a pair of nine foot towers not four) volume and provide force cancellation to limit structure borne vibrations which could pose problems with floppy floors radiating and sound transmission.

http://www.linkwitzlab.com/woofer.htm

Previously I stated that in a domestically friendly 14" deep enclosure excrusion was 4X that of a monopole and by 20Hz you have 8X the excursion. That's enough to get noticeable movement at high levels in a 70 pound enclosure with a pair of forward facing drivers at the bottom. It's not audible on a rigid floor (radiation from the rocking cabinet is dipolar and therefore rolling off at 6dB/octave due) but could be problematic otherwise.

>The effect would be much the same as a boxed speaker. Ya, I can see how it bring more control to high Q drivers and reduce that boomy sound.

It has nothing to do with a boomy sound.

>The "Direct Servo", along with suitably designed drivers, ameliorates that condition to some degree.

Using electronics you can adjust the system high pass response to pretty much anything you want. Siegfried Linkwitz likes a second order high-pass Q=0.5 with resonance at 20Hz. It sounds good and I've never bottomed my woofers on music (I'm getting 105dB peaks on acoustic recordings with a lot of dynamic range and have had modern music at 95dBC SPL average). John Krevosky has suggested allowing a third order roll-off below system pass-band so subsonics are less an issue (second order acoustic roll-off means excursion is still doubling with each octave lower at a given program material level until you pass the woofer's lowest pole which can be in the single digits for a low-Q woofer). That can be a problem with vinyl though.

DanielK141

thanks for the heads up on the offer on ebay.

The price on that listing is already >$500 and $250+ on shipping. So I'll keep an eye out on that as long as it doesn't get too expensive. I will make a bid on it.