[AlliumPorrum]

I have a dream; to build 3-way active setup with my Magneplanar 2.5's, DEQX, and some DIY dipole basses. The reason for this is that I really really like the mids and highs of Maggies, but regardless of the Maggies' size, I alway feel that there is something missing from the bass section. So, I would like to build some dynamic dipoles, and low pass them with DEQX somewhere near 100-200hz. With DEQX it is quite easy to try different setups anyway, and also do the driver- and room corrections.

I have had a Rythmik Audio subwoofer in a sealed box, and I really liked it's sound. So, using GR 12's and RA amps is quite natural option for me. I think I'm going to use 3 x GR 12 per side, since one RA amp can drive 3 elements.

But, since I don't have any experience on dipoles yet, I would like to get some help on following issues:
- For the same price, are there any better drivers that GR's? What are their weaknesses, if any?
- What's your opinion on the optimal lowpass frequency, if using 3 pieces of 12" GR per side? Once again, I'm not looking for a subwoofer just to fill up the range below Maggies, but a bass unit that gives best possible punch and dynamics and also goes down to 20-30hz. Maggies would be playing just the mids and highs.
- What kind of baffle would be the best option for such bass unit? OB/H/U/W or what? For what I have read, I've understood that the H- would be a good solution in most cases, but what's your opinion? I also think that W wouldn't be a good idea when going over 100hz..?
- How about the baffle size? What would be optimal size (width, depth) when using 3 pieces of 12", and going up to 100-200hz? What is the relationship between the lowpass frequency and baffle size after all? I mean; do I have decide the exact low pass frequency before building the baffle?

All comments are highly appreciated! :=)

[sfdoddsy]

Do you need the extra volume of 3 drivers a side?

If not, I'd just go with two drivers the same depth as the H-Frame on the GR site, ie 13.5". 2 drivers back to back will have some advantage in distortion over 3.

The deeper the frame, the lower you can go, but you will need to cross them over lower too.

The GR solution would be easiest because it comes as a package and you don't need to worry about separate EQ and amps.

[studiotech]

The GR servo open baffle woofers are really very excellent.  Best bass at RMAF several years.  I came really very close to using them on my own project, but went with a sealed pair of Rythmik for below 60Hz.  For all but the most extreme cases, 2 12" per side should be fine.

Greg

[AlliumPorrum]

Thanks for your replies! I don't think I need high pressures, so maybe 2 drivers per side would be just enough. When using 12" SLS's, I know that even 4 per side isn't too much, from the sound quality point of view. I mean; with 4 drivers they have to move only half of that with 2 drivers -> less distortion, tighter sound. But maybe this is not an issue with servo's..?

What might be a highest feasible low pass with that W- frame from GR's site?

[stevenkelby]

What might be a highest feasible low pass with that W- frame from GR's site?

200hz

 

[JohnR]

AlliumPorrum, I've heard a system with 20.7s and a DEQX to manage them and separate subs, albeit sealed not dipole. I'd say you're in for a treat, although the learning curve seems to be substantial. Do you have the DEQX already?

[AlliumPorrum]

JohnR, no I don't have the DEQX yet. Thinking between the new HDP-4 and possibly second hand HDP-3.

[jk@home]

I know this is the OB forum, but as a Maggie owner (highly modded MMGs) I have to recommend a pair of Infinite Baffle subs. Clean deep bass without the footprint of a big OB array. You will need twice the drivers in an OB to get the same output as an IB, which means large driver panels to add to your room, which effects the planars. My IBs are over the main speakers in the attic.



But all that's seen is:



Highly recommended.

[persisting1]

How do you have the sub isolated from the attic floor?

[jk@home]

It's not, bolted right to the lumber. SOP in IB construction.Check out the Cult of the Infinitely Baffled web site. If you register, look up "johnvb's IB project in the "My projects" section., I go into detail of the build.

[Davey]

Allium,

Are you capable/interested in building something?

I think the GR approach would be fine, but darn expensive.  A DIY approach is preferred.

Look down at the bottom of this page to see the dipole woofers I implemented on my MMG system a few years ago.

http://home.comcast.net/~dreite/MMGframe.htm

Standard "H"-frames with two 10" drivers per side.
The tricky part is the active crossover.    It's a custom build and dedicated exactly for this type of usage.  A silly gadget like the DEQX is complete overkill and waaaaaaay too expensive for a simple job like this.

Cheers,

Dave.

[studiotech]

The GR is DIY.  Not really all that expensive for the performance you get....I think if he's considering a DEQX, price is not a major concern.  Not that spending more than is necessary is advised, but I'm just sayin...

As far as DEQX, yes it is pricey, but does so much more than just Xover functions.  They are still the only game in town for an integrated solution that's as powerful as they are and are worth it if looking for ultimate performance.

Greg 

[Davey]

The problem with the DEQX is that it won't do what's required for this application.  The user does not have direct control of the necessary EQ/xover for this type of integration.

If a person wants to futz around performing "room correction" it's a  handy....but very expensive gadget.

The GR Research is pretty much DIY, but not totally.  And you still don't have direct control of the required EQ.  Four woofers and two power-amps and you're well north of $1000.00 immediately.

Dave.

[studiotech]

Hmmm, it was my understanding(possibly wrong) that you could set Xover and EQing manually rather than use the fully automatic settings and then run room correction and phase correction voodoo.

Greg

[JerryLove]

You cannot build dipole subwoofers (unless the baffle is humongous) because subwoofers are already omnipolar.

You could put drivers on either side, or you could open the back of the driver (unenclosed); but it would still be omnipolar.

The following article is on baffle diffraction: but anything below the effect of the baffle is omnipolar.
http://trueaudio.com/st_diff1.htm

[Davey]

Hmmm, it was my understanding(possibly wrong) that you could set Xover and EQing manually rather than use the fully automatic settings and then run room correction and phase correction voodoo.

Greg

If it does, then they've changed its capabilities.  But even if it did what would be the point since the whole concept of the device is to relieve the user of the nut/bolts of speaker system design?

It's a whole lotta money and computing horsepower for a gadget that fixes problems that aren't really problems (like non-linear phase response,) and implements a completely flawed concept whereby you "correct" your room by modifying the frequency response of the speakers.  How does that make sense? 

Anyways, this thread is about integrating dipole bass systems with Maggies.  The DEQX is completely off-topic for the thread.

Cheers,

Dave.

[Davey]

You cannot build dipole subwoofers (unless the baffle is humongous) because subwoofers are already omnipolar.

You could put drivers on either side, or you could open the back of the driver (unenclosed); but it would still be omnipolar.

The following article is on baffle diffraction: but anything below the effect of the baffle is omnipolar.
http://trueaudio.com/st_diff1.htm

"Traditional" subwoofers are omnipolar (monopole) because they're closed or vented boxes which either block the rear radiation or store it for later use, respectively.

However, subwoofers don't necessarily need to be "traditional."  "Sub"woofer is more a definition of frequency range vice implementation...IMO.  Dipole woofers can certainly perform to "sub" frequency ranges if so desired.  You do run into the physics and it might not make sense because of the trade-offs required, but it's certainly possible.  And they're still "dipoles" and not "omnipoles."

John Murphy's article is mainly discussing baffle-step correction for conventional speakers.  An effect usually at much higher frequencies.
When venturing into dipoles, many of the traditional design techniques/corrections become unnecessary and/or meaningless

Cheers,

Dave.

[AlliumPorrum]

Davey, this really isn't about DEQX, so lets please stick in the topic.

But, just to sure that no one is getting this wrong, you should check the DEQX- page: http://www.deqx.com. Few points about the HDP-4:

- "It normally is applied to 3-way active or 2-way active plus subwoofer configurations, so that each driver can be individually compensated. The crossovers in DEQX-HD™ are true linear-phase, usually with steep slopes in the order of 48dB/octave to 60dB/octave."
- "It provides the ability to correct – directly from measurements – both phase (timing) errors and amplitude (frequency-response) errors at hundreds of frequency groups to within a fraction of a decibel"
- "DEQX processors provide both speaker correction and room correction. Each require a different type of measurement and correction process because speaker correction means that the speaker must first have its errors measured anechoically (without room reflections) to allow its frequency-response errors and its frequency-related timing or phase errors (group-delay errors) to be determined."

So it really is NOT about the room correction, and I think there isn't any other device that offers such functionality.

[Davey]

It wasn't me that brought up the DEQX. 

Yep, I'm well aware of the DEQX advertised capabilities regarding speaker correction and room correction.  I'm only saying (for me) it wouldn't allow the flexibility I'd need to implement a dipole woofer system.

When the DEQX provides the capability to physically reshape/resize the baffle and other aspects of your speaker system, then it'll have speaker correction capabilities. 

Cheers,

Dave.

[JerryLove]

"Traditional" subwoofers are omnipolar (monopole) because they're closed or vented boxes which either block the rear radiation or store it for later use, respectively.

If a closed box is omnipolar, you can't expect an open driver to be *less* omnipolar.

Unless your baffle is large enough to cause beaming in the frequencies involved, your baffle will be irrelevant and your driver will be omnipolar.

Though without a box, you will get wave interactions between the front and back of the driver. This will not affect directionality, but will change the wave interference paterns.

Dipole woofers can certainly perform to "sub" frequency ranges if so desired.  You do run into the physics and it might not make sense because of the trade-offs required, but it's certainly possible.  And they're still "dipoles" and not "omnipoles."

The sound output will be uniform (before wave interface) in 360 degrees.  They will be omnidirectional (just as all subs are).

John Murphy's article is mainly discussing baffle-step correction for conventional speakers.  An effect usually at much higher frequencies. When venturing into dipoles, many of the traditional design techniques/corrections become unnecessary and/or meaningless

The physics of sounds on a surface do not change. I've run dipole. I've run true omni (well, as true as it gets).

At the frequencies involved, unless the baffle is huge, every driver will radiate omni-directionally. If you don't put a box behind the woofer, you'll simply have a 180-degree-out-of-phase second driver that is the back of the cone.

Same thing if you use a huge plane (or low SPL) and run electrostatic or ribbon.

I'm not saying it's good or bad; what I'm saying is that it's different from HF output where monopole speakers are not already omnidirectional.

But you tell me: What is the difference in radiation pattern between any conventional sub putting out (say) 60Hz, and whatever you are thinking of as "bi-polar" doing the same thing?