Are Dipole & Monopole Servo Subs Compatible?


New Member
Jan 14, 2017
In my 14 ft x 19 room I have a cloned pair of Gary Dahl’s two-way mains: Aurza 425 horns/Radian 745 Neo/Be drivers atop sealed GPA Altec 416-8B midwoofers.

The Altecs go down to 70Hz, below which my pair of Rythmik 12" sealed servo subs take over. However, studies done by Todd Welti show conclusively that using 3 to 4 subs even in small rooms will better quell room modes and thereby yield much smoother bass response throughout much of the listening area. See Figs 47 thru 53 bare out the results, and especially Figs. 40 and 41. - 06:12/files/multsubs.pdf

There’s also a thread on the subject where Earl Geddes discusses his somewhat different multi-sub solution for achieving similar goals.

Based on Welti’s conclusions to reduce room modes, I was then going to order the second pair of Rythmik 12" sealed subs for the above system. Both pairs of subs can be daisy chained as they would all have the Rythmik A370-XLR2 plate amp.

However, I also want to install another system in the same room placed along the short wall opposite my other system. The mains for that system would be a pair of ESLs, probably Quad 57s or 63s.
However, even raising the Quads 15 to 20” on stands and placed seven feet from the rear wall, the Quad 57s will only do down to 40Hz at best, ergo subs for that half octave or so. But as ESLs, like open baffle speakers, are dipoles, I presume that a pair of dipole rather than sealed monopole subs would sound best for the Quads. And I found a thread proposing dual 12” woofers in OB cabinets, servo controlled by the Rythmik plate amps fitted with a shelving filter.

These dipole servo subs appear to be in use by one Quad 57 owner.


1.) Would my two way hybrid horn/sealed Altec midwoofer (monopole) speakers sound fine if one pair of subs were dual 12” Rythmik servo dipole subs?

2.) Would the Quad ESL (dipole) speakers sound fine if one pair were of subs were Rythmik 12" servo sealed box subs?

3.) And would the sealed pair and the dipole pair of subs still reduce room modes as effectively as if all 4 subs were identical?

Assuming the answer to all the above is yes, there’s the matter of setting the crossover frequency for both pairs of subs, when using either pair of mains.

My Altec midwoofers play down to 70Hz. And the Quads, if placed 6 to 8 ft from the rear wall-and if raised 14 to 20” on (Arcaci) stands-should do down to between 45 and 40Hz.

Accordingly, I would initially set the sealed subs and the dipole subs plate amps to cross and be in phase with the Altec midwoofers and Quad ESLs, respectively, and confirm that each pair of subs works nicely with alone with its own mains.

Btw, I would need to note these settings for each subwoofer pair to supply bass to its own mains, as the Rythmik plate amps have no memory for storing multiple groups of subwoofer settings.

Likewise, I would need to adjust the dipole subs to blend with the Quads.

Then when playing the pair of monopole mains I would then have to readjust the dipole subs to properly cross and be in phase with these mains.

Alternately, when using the pair of dipole mains I would then have to readjust the monopole subs to properly cross and be in phase with those mains.

Now the question is, whether I use the pair of monopole or pair of dipole mains, how well would you expect these pair of daisy-chained dipole subs and monopole servo subs to sound together when both pairs (properly crossed and phase adjusted) are for playing either pair of mains?

And at the same time, regardless of which mains I’m playing, will a pair of dual 12” Rythmik servo controlled dipole subs work well with my pair of Rythmik 12" servo sealed subs to minimize room modes?

Last but not least, while deciding which part of which forum to place my post I found some unexpected controversy on the very notion of open baffle subs. A “stupid idea”? I’m probably not expert enough to even enter into a debate on this. However, in order to avoid making a bad investment and/or overcomplicating my subwoofer scheme, I am reaching out for experienced and impartial feedback on dipole subs, dual 12" Rythmik servo dipole subs in particular and using them simultaneously with Rythmik 12" sealed servo subs. Thank you.
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