Others experience re: subs and Magmepan 20

Reviewing Rhythmik or Salk (upgraded cabinets with same components) as option.

Anyone care to opine as to whether or not a 12" vs 15"  has inherent advantages for music (no movies) where max sound pressure at seat 100dB and usually far less?  I do have some space constraints and the 15" might be problematic physical wise.  12" is front firing and 15" downfiring and I don't know how to assess what this would do.

Also putting subs behind the Maggies *seems* like a bad idea as I envision the sub output pounding the Magnepan panels and modulating its output.  My thought was to put the sub beside the Magnepans.   Any opinions as to whether this is a real or imagined issue in real world?

Thanks

Thank you for your kind words, imdoc! I enjoyed talking with you very much. One thing I forgot to mention - you’ll probably have to EQ in a fair amount of low-end boost in your room. I suspect that the big opening behind the listening area is acting sort of like a bass trap and reducing your in-room bass. You might also experiment with putting the two subs in phase quadrature (90 degrees apart) - it may be beneficial.

Tim, if you look up imdoc’s system (just click on his name), you’ll see a photo of his room. It is a beautiful space that is not a dedicated audio room, and in my opinion multiple subs distributed around the room would ruin the aesthetic he has achieved.

The room is open at the end that’s "behind your back" from where the photo is taken, so that room dimension is not distinct. The other room dimensions (width and height) don’t support room modes below 30 Hz, and he’s only looking to augment the Maggies south of 30 Hz, so the net value of the modal-region-smoothing we get from a distributed multi-sub system doesn’t apply as much. In this situation, I think the more cost-effective and aesthetically practical solution would be two high-output subs that fit in the areas behind his Maggies.

At first I was thinking that a pair of tall two-woofer subs dimensioned to fit behind the Maggies (and shaped to be Maggie-backwave-friendly) might work well, as with one woofer high and one low, we’d at least have our bass sources distributed in two dimensions (height and width). But then I thought about his room dimensions and the modes those dimensions would support and decided that the benefits would be minor, and that it would be more cost-effective for imdoc to just get two powerful conventional subs rather than paying to have expensive custom enclosures built. So I suggested he look at Rhythmik, though they are by no means the only viable choice out there.

Duke

Thank you very much, Tim! Glad the Debra is working well for you!

The only question mark in my mind regarding imdoc’s situation is, whether his room has something going on (large area and/or open floorplan perhaps?) that results in minimal boundary reinforcement in that bottom octave. It sounds to me like his primary issue is a shortfall in bass quantity, to the extent that if there is a qualitative mismatch between subs and his big Maggies, it hasn’t been obvious yet.

Both the Debra and the Swarm are "voiced" with the expectation of about 3 dB per octave of gain from boundary reinforcement below 80 Hz or so. There is a fair amount of adjustability built in, between the equalization available in the amp and the other setup options, but it is possible that he needs more bottom-octave energy than our systems provide in their "stock" form.

So while I think we have a good solution in the room-interaction domain, in this particular situation I don’t know whether we’d meet the quantitative requirements. Not that the four 10" subs in the Debra and Swarm systems are wimpy (their motor strength is unusually high, and many of our customers have measured in-room -3 dB points around or below 20 Hz), but maybe he’d be better served by four 15" subs that are voiced "flat" rather than voiced with typical boundary reinforcement taken into account.

Duke

I designed the Swarm subwoofer system mentioned above, and worked with Jim Romeyn on his conceptually-similar Distributed Bass Array system.

The Swarm was originally designed with dipole speakers in mind, specifically Maggies and Quads. Briefly, dipoles have smoother in-room response in the bass region than monopoles do (according to a peer-reviewed paper by James M. Kates). Smooth bass is fast bass, subjectively and literally - in the bass region, in-room peaks happen where the energy decays more slowly, and vice versa. In fact, the two are so interconnected in the bass region that if you fix the frequency response, you have also fixed the time-domain response. So the key to matching the "speed" of dipoles is, match their in-room smoothness.

Two subs intelligently positioned will be roughly twice as smooth as one sub. Still not as smooth as two dipole main speakers, but definitely better than one sub. Four intelligently positioned subs will be twice as smooth as two, and comparable in smoothness to a pair of dipoles.

The improved in-room smoothness that arises from using multiple subs intelligently distributed may seem counter-intuitive, so let me try to explain: Imagine you are looking at the in-room frequency response of a single sub. You see a few big peaks and dips. The problem is not only their magnitude, but also how far apart they are - you see, the ear/brain system tends to "average out" peaks and dips that are within about 1/3 octave of one another, but these are almost always going to be further apart than that. Small rooms are typically worse than big rooms in this respect.

(Also, the ear is especially sensitive to changes in loudness - peaks and dips! - in the bass region. This is shown by the way that equal-loudness curves bunch up south of 100 Hz. So there is usually a LOT of room for improvement in the bass region.)

You can move the sub or move the microphone location and those big peaks and dips get shuffled and changed, but they do not go away. Now imagine that you add a second subwoofer in a different location. It too generates a big peak-and-dip pattern. But unless the second sub’s peaks and dips overlay the first’s (which can only happen if the two subs are in the exact same spot), the sum of the two will be significantly smoother than either one alone. Mathematically, it will tend to sum to half as much average deviation (or "twice as smooth"). The same trend holds as we add more subs. And not only are the peaks and dips smaller in the summed response, but they are also more numerous and therefore closer together, so the ear/brain system’s averaging characteristic comes into play, and the subjective improvement is probably greater than one might think from eyeballing the summed curve.

Anyway my point is, there is some solid acoustic and psychoacoustic science behind the distributed bass array concept. Credit to Earl Geddes for sharing his ideas with me and allowing me to use them.

Duke

Jim, Rythmik Audio has two sealed subs featuring dual 8" woofers, the F8 and FM8. The only difference between them is the FM was designed to be used as a mid-bass woofer, it’s x/o to a lower-frequency sub being 4th order at 50Hz. Both operate up to 250Hz, and both incorporate the Rythmik Direct Servo-Feedback amplifier.

Also, co-designed by Rythmiks Brian Ding and Danny Richie of GR Research is the unique OB/Dipole Sub, available with dual 8" woofers, though dual 12’s is the more common choice. This OB/Dipole Sub is the ultimate sub for use with all planar speakers, for obvious reasons.

By the way, both Brian and Danny are adamant that because of the design of the 8" and 12" woofers (designed in house specifically for open baffle implementation, and custom manufactured by TC Sounds for Rythmik and GR exclusively), and how they are controlled by the Rythmik Servo-Feedback circuit, the 12" is just as "fast" as the 8", but capable of considerably more output. The sense of "speed" in a woofer is in how quickly it returns to "rest" after the signal has stopped, not how quickly it starts (Rythmik/GR subs have been described as "stopping on a dime"). Subwoofer frequencies are relatively "slow", but woofers, once set in motion, tend to stay in motion. That’s where the Rythmik Servo-Feedback circuit comes into play. If you’ve ever heard the Infinity IRS loudspeakers, you know what I’m talking about. I formerly owned the mini-IRS, the RS-1b (featuring six 8" servo-feedback controlled woofers per side), and the pair of Rythmik Audio/Gr Research subs I now own are considerably better. Leaner, cleaner, no boom, no bloat. It’s the only Open Baffle/Dipole Servo-Feedback Sub in the world! Seriously, if you don’t have room for a pair of Magneplanar Tympani T-IV bass panels (great as subs for Maggie MG series speakers), this is the sub to own.

http://jamesromeyn.com/old-pages/home-audio-gear/dsa-1-0-distributed-subwoofer-array-5-pieces-4k-usd...

Since it is such an ideal system for me and I think it would work well in your system, I provided a link to  the Absolute Sound's 2015 review of the Audio Kinesis SWARM (which awarded it a 'Golden Ear' award for that year) below:

http://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/

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    I can personally attest to the effectiveness of the DEBRA system in my room. I have 6 listening/viewing positions in my combination music and ht system in my living room. Bass response is equally good for music and HT at all 6 positions without the use of acoustic devices (no absorbing or diffusing panels or bass traps) and without any electronic equalization (room analysis/correction equipment, software or eq). I should mention I've never had my system/room analyzed using a mike and software.  

    From my purely subjective perspective, however, I'm confident the results would be good since I spent hours on the setup and critical listening from all six listening positions in my room. I would suggest this type of sub system as a viable alternative for anyone considering investing in one or more quality subs. The system is rated clean at 113 decibels at 20 hz and I've often heard and felt it go this low.  It feels and sounds clean and right but I can't verify the decibels or lack of distortion.

Hope this helped,

  Tim

imdoc---akg_ca’s repost included a few assertions (well, a lot more than a few, and I didn’t make it through the whole thing :-) that must be disputed.

1- "it is virtually impossible to build a really good subwoofer for under $1000. Yet most of the subwoofers out there sell for between $500 and $900."

First, it is NOT impossible to build a really good subwoofer for under $1000. There are a fair number of Maggie owners very satisfied with their Rythmik F12G subs, to name just one under $1000 sub. I have heard the Vandersteen subs, very fine products, on many occasions, and while not wishing to pit Vandersteen against Rythmik, I can safely say that anyone who is satisfied with the Vandersteen is very unlikely to not also be so with the Rythmik. In fact, one’s preference might flip after having heard both.

But come on akg, do you really think the owner of Magnepan MG20r’s is limited to a sub-$1000 (no pun intended) subwoofer?! There are a number of incredible subs available which are valid competition to the Vandersteens, if funds are available.

2- "This is the only subwoofer (referring to Vandersteen of course) that is specifically designed to be inserted into the highest of high-end music systems without doing any harm to the precious signal."

What a ridiculous, arrogant statement! That is patently false. Whoever wrote that sentence must be woefully ignorant of the products of a number of designer/manufacturers who set their sites on that exact goal. Richard Vandersteen is not the only talented speaker designer out there, for gawds sake! I could name a few, but I’ll just mention Danny Richie and Brian Ding, of GR Research and Rythmik Audio respectively. Brian Ding designed his line of subs (which incorporate Mr. Dings patented Direct Servo-Feedback technology) for music reproduction, and Danny Richie and he collaborated on a 12" driver offered with either an aluminum cone (for high volume application, including loud music and/or home theater) or a paper one (the "G" in the model designation of the Rythmik F12G, which uses the paper-cone version of the woofer, refers to GR Research) specifically for music listened to at less than extreme volume, it’s lower mass providing higher low-level resolution.

In addition, they also collaborated on a very unique subwoofer designed specifically for "the highest of high-end music systems"---an open baffle/dipole sub (two 12" woofers mounted in an OB "H-Frame", powered by the Rythmik Servo-Feedback amplifier), the ultimate design for mating with a dipole speaker such as Maggies (and ESL’s, and Ribbons). The GR Research/Rythmik Audio OB/Dipole Sub is, and I say this with the upmost respect, a completely different animal than the Vandersteen, and all other, sub(s). Is the writer of the quoted sentence even aware of GR Research and Rythmik Audio products, or all the other high-end designs now available?

3- "In fact his (Vandersteen) crossover is so ingeniously simple that it is a wonder nobody else thought of doing it the same way."

It IS simple, and it WOULD be a wonder if nobody else thought of doing it the same way. But they DID, and a long, long time ago! Advanced enthusiasts having been employing a simple 1st order crossover as a high-pass filter since the 1950’s. You don’t really believe no one before Richard Vandersteen thought of something so obvious, do you?! The Dahlquist x/o in the 1970’s used that exact technique---a single capacitor to filter the signal going to the main speakers.

Now, if you’re talking about Richards technique of taking the signal for the sub from the speaker taps of the main power amp, Richard is not the only one doing that either. Both Rythmik Audio and REL offer the same hookup, Rythmik also providing line-level connections.

All of this is not to say that the Vandersteen subs are not very fine products. Far from it---they are great. But they are not the only really good ones available for use in "the highest of high-end music systems". They do have some competition, and may in fact have some which surpass them. There are even Magneplanar fanatics who use the Tympani T-IV bass panels as subs for their MG series Maggies!

First iteration of monkeying around: Janis subs are crossed over at 35 Hz at  24 db/octave

Thanks to all who have responded