[emailtim]

I have a pair of Mini-Maggies/DWM combo and am looking for a seamless subwoofer option for them. 

I have been reading about the W and H-Frame dipole OB projects.  Both of these cabinet options are rather tall for an office and having 4 drivers would probably be overkill.  I was wondering if instead of making a pair of stacked H-Frames(4 drivers/2 servo amps/2 dual driver cabinets), how 2 separate single height H-Frames(2 drivers/1 servo amp/2 single driver cabinets) would work. 

The combined signal would still be mono driven by one servo amp, but would facilitate more placement options with 2 smaller cabinets and possibly minimize localization issues.

Any ideas?

Excuse the cheesy character diagrams.

Stereo Stacked H-Frames:

     I0I             I0I
     ---             ---
     I0I             I0I

Dual-Mono Single H-Frames:

     M             M
     ----desktop----
     I0I   DWM   I0I

[Danny Richie]

That would make quite the desk top system.

If they do indeed play down to 40Hz then a single mono sub will work fine.

Keep in mind though that with the Maggies and open baffle subs, they don't work well up against a wall. They need to be at least three feet or more away from the wall behind them.

[emailtim]

That would make quite the desk top system.

If they do indeed play down to 40Hz then a single mono sub will work fine.

Keep in mind though that with the Maggies and open baffle subs, they don't work well up against a wall. They need to be at least three feet or more away from the wall behind them.

Hi Danny,

I tried a Martin Logan Descent with the Mini-Maggies @ 70Hz, but it was way-overkill.

For the MiniMaggies, I was planning on crossing them over @ 80-100Hz (after experimentation).  For the larger panels, I would cross them over lower.  I do not have 3 foot on the desktop system and the MiniMaggies sound quite nice.  I have more than 3 foot on the larger panels.

I also thought about mounting the drivers in the desk-well panel under the MiniMaggies since the desk is pretty wide(@ 6 ft), but there might be vibration issues to deal with.

Thanks,
Tim

[Danny Richie]

Hi Danny,

I tried a Martin Logan Descent with the Mini-Maggies @ 70Hz, but it was way-overkill.

For the MiniMaggies, I was planning on crossing them over @ 80-100Hz (after experimentation).  For the larger panels, I would cross them over lower.  I do not have 3 foot on the desktop system and the MiniMaggies sound quite nice.  I have more than 3 foot on the larger panels.

I also thought about mounting the drivers in the desk-well panel under the MiniMaggies since the desk is pretty wide(@ 6 ft), but there might be vibration issues to deal with.

Thanks,
Tim

Because of your space limitations you might want to just use one of our sealed box servo subs.

[doug067]

MFW-15 compared Servo sub cabinet

[emailtim]

What would a Ripol[e] type cabinet do to the SW-12-16FR response?  Would it be consistent with an H-Frame ???

http://lautsprechershop.de/index_hifi_en.htm?http://lautsprechershop.de/hifi/ripol_en.htm

[Hank]

Good question, emailtim - I'd forgotten about the ripole method - wonder why it's not used more.

[jparkhur]

Danny,  How would the servos work with this??

See link to ripole project   http://jazzman-esl-page.blogspot.com/2011/01/ripole-subs-are-underway.html

[Danny Richie]

Good question, emailtim - I'd forgotten about the ripole method - wonder why it's not used more.

Because they are buzz boxes. Typically the back panel is just a large un-braced panel. And they put a lot of pressure on the driver just like a sealed or ported box, and it tunes them very high. Plus the front to back (or front to side) cancellation effect is immediate. So you get only a fractional amount of output that the woofer will be capable of.

[Danny Richie]

Danny,  How would the servos work with this??

See link to ripole project   http://jazzman-esl-page.blogspot.com/2011/01/ripole-subs-are-underway.html

Ah, the super buzz box deluxe model.

I'd love to see an impedance sweep on those things to see how high they are tuning them.

I think it might work great in car audio as a trunk mounted design firing through something that would vent one side into the car and the other side into the trunk.

[eparson]

Having built both the H Frame and ripole utilizing the same woofer, I can say that the sound is very similar, you do lose some sensitivity with the ripole, but the FS is lowered and not raised by about 4 or 5 hz.  I have not experienced the "buzz box" sound that is referred to above.  If you are concerned with sensitivity, then by all means go with the H Frame.  If not, the more compact size and lower fs makes the ripole an attractive alternativie.

[Danny Richie]

Unless you glue the back panel to the magnet of the woofer then you have a pretty large un-braced panel. And that panel sees a lot of pressure. There would clearly be some resonance issues there. If you made it a couple of inches thick (maybe three layers of 3/4" MDF) then you might be okay.

I'd be real surprised if it lowered the Fs. It looks to me like it would raise it. I'd really like to see an impedance sweep.

[emailtim]

Danny,  How would the servos work with this??

See link to ripole project   http://jazzman-esl-page.blogspot.com/2011/01/ripole-subs-are-underway.html

I read that thread last night as well as the following thread, but it just ended without any final explanations, just measuring software difficulties.

http://www.audiocircle.com/index.php?topic=94339.0

I read that the design is supposed to lower the frequency by @ 10Hz, but don't know if that requires the dual driver version or if the single driver version also has the lower extension.

The German site's instructions indicate using 1" panels (24mm actually) for the 2 lids and (12mm+12mm) for the driver mount.  The 18" build looked like it used 3 layers per panel.

As for the buzz-box, I would think that the 4 full length assembly screws would add tension to both lids to further reduce the vibrations like adding sand/led shot bags or amp-clamps to a chassis.  I guess this depends on where the full length screws are located.  If the center panel was threaded (or standoff tubes were used like in the 18" build), it could also benefit from these 4 assembly screws.

When I ran frequency sweeps on my first home-theater system, I found one frequency that made the lid on a CD player buzz like crazy.  Another frequency made the blinds rattle and another frequency made the back shroud on the 35" tube TV buzz.  Adding compression pressure to both the lid of the CD player and the TV's shroud eliminated the buzz at their respective frequencies.  Maybe the 4 tension screws serve a similar purpose ???

[eparson]

I should have mentioned that I use the dual drivers with the threaded rods for tensioning.  My measurements showed that it lowered FS by 5 hz.  I have no vibration issues.  The only thing I can say is try it and then decide, that is what I did....YMMV

[emailtim]

I should have mentioned that I use the dual drivers with the threaded rods for tensioning.  My measurements showed that it lowered FS by 5 hz.  I have no vibration issues.  The only thing I can say is try it and then decide, that is what I did....YMMV

What formulas did you use to calculate the chase sizes? 
Did you round the back of the chases?
What frequency range are you getting?

Thanks,
Tim

[Danny Richie]

I read that the design is supposed to lower the frequency by @ 10Hz, but don't know if that requires the dual driver version or if the single driver version also has the lower extension.

You should get two impedance rises just like a ported box. The dipped area in the middle is the tuning frequency of the box.

The German site's instructions indicate using 1" panels (24mm actually) for the 2 lids and (12mm+12mm) for the driver mount.  The 18" build looked like it used 3 layers per panel.

That is not a bad start.

As for the buzz-box, I would think that the 4 full length assembly screws would add tension to both lids to further reduce the vibrations like adding sand/led shot bags or amp-clamps to a chassis.  I guess this depends on where the full length screws are located.  If the center panel was threaded (or standoff tubes were used like in the 18" build), it could also benefit from these 4 assembly screws.

Yes, it depends on where they are located. Think of the panel like a drum head. Something supporting it in the middle will have good effect. Something supporting it at the outer edges around the frame will have little effect.

When I ran frequency sweeps on my first home-theater system, I found one frequency that made the lid on a CD player buzz like crazy.  Another frequency made the blinds rattle and another frequency made the back shroud on the 35" tube TV buzz.  Adding compression pressure to both the lid of the CD player and the TV's shroud eliminated the buzz at their respective frequencies.  Maybe the 4 tension screws serve a similar purpose ???

You are talking about the resonance frequency of each of those devices being hit. Each of the panels on any enclosure has the same effect. Panels can also flex greatly at levels far below the resonance frequency. Try laying your hand on those side panels while it is playing hard and see what you feel.

Do you have any impedance sweeps that you can share?

[emailtim]

Do you have any impedance sweeps that you can share?

I can go thought the threads again to see if they have any impedance sweeps. 

As for my build, I am waiting for your drivers to be delivered to try 

When I read lowered frequency and smaller size, it got my attention.

[Davey]

Danny,

Two impedance peaks like a ported box?  (Not if a dual-drivered setup is loaded the same.)  This is not a ported box, per se, with all the associated energy storage.

It seems you have a basic misunderstanding of the Ripole concept.

http://lautsprechershop.de/hifi/aka_sub_sonder_en.htm

The possible panel vibration is a secondary issue and not directly related to the driver loading technique to lower Fs.
Whether the trade-offs of this technique add up effectively is, I guess, subject for discussion, but the concept seems straightforward enough.

Cheers,

Dave.

[Danny Richie]

Hey Davey, It would really depend on the size of the air space that the driver sees and if it sees it as a small box with a large but very short port or as just a pressure loaded driver in free air. The impedance curves would tell.

No misunderstandings here. I know cabinet vibrations are a secondary issue, but still a big issue that must be addressed.

[Davey]

There's an example impedance curve on the page I posted.

Of course, if the air space the driver sees is modified such that a double impedance peak would emerge then the objective of the Ripole configuration has been abandoned.

I don't see the point of this (Ripole) configuration myself.....unless space is really at a premium.  Lowering roll-off frequency and characteristics can be accomplished electronically without resorting to this type of complicated construction.

Cheers,

Dave.