Got M&K MX-150 THX for Maggies... feelings?

Nsgarch: My earlier system consisted of a Dahlquist DQLP-1 passive Hi/active low filter, which placed all of one capacitor(a polypropylene) in the mains signal path(minimum phase shift). Virtually transparent! I attenuated my volume with a Placette passive for years(again virtually transparent). One object of actively bi-amping with subs is to rid the mains of the intermodulation distortion created when the diaphram is trying to reproduce frequencies below it's capabilities(and they ALL try). One of the same reasons crossovers are used in multi-way speaker systems of any design. There isn't nearly enough capacitance in the voice coil(so to speak) of the Maggies to electrically roll of the low bass. Another benefit is the fact that it takes much more power to reproduce bass frequencies than mids and highs(although the greatest part of the music is in the midrange). By removing this load from the main amps, a very noticable/audible improvement is appreciated(as I previouly mentioned). The TacT that I used to replace the afore mentioned filter and attenuator is a state-of-the-art unit that has received raves from a number of high end publications(Editors Choice from The Absolute Sound, Robert Harley, etc.), and adds/subtracts nothing appreciable from the original signal(and I am VERY critical). Regardless of your improvements: NO room will sound like an original recording venue(unless it IS). As mentioned in many of the reviews it has received: the Tact units bring the listener very close to this ideal. I've been deeply involved in professional sound for the past 26 years, and my frame of reference has always been live music(which I am blessed to hear 2 or 3 times a week). The idea that there is no directionality in the bottom octaves, or that subwoofer placement doesn't matter has to originate with people that have never heard properly reproduced sound(or live music, ala Julian Hirsch). Many people are happy just adding bass to a system(whether the result is true to the original signal/sound/recording venue or not). There is a massive difference between dipolar(planar) and bipolar systems(the infinite baffle cones you referred to) by the way. Their radiation pattern/phasing is totally different. Steve: I don't know how much live music(acoustic or amplified) you get to listen to, But- If your reference(or goal) is accurate/live sound: Don't let anyone disuade you from trying a (correctly)bi-amped system. Too many opinions and not enough trained ears in these forums for me to indulge. Goodbye and Happy listening!!

Bob, first I'd just like to say that I feel it's probably a mistake to make generalizations about any speaker "type" be it horns, or boxes, or planar (magnetics or stats) etc. Some are very good at everything (they do) and others not. This is less true of planars but only because they're relatively harder to build, and so there's no profit in making crappy ones ;--) So saying that "a conventional box speaker produces more distortion in the bass region by either increasing SPL or decreasing frequency" is simply not true for the majority of decently designed and built box speakers operated normally (ie with a flat signal.) And I'm not just referring to megabuck products.

For the sake of discussion, I prefer to say dipoles because some "planars" are curved, and not all dipoles are planars -- some are infinite baffle cones. So, except for Soundlabs electrostats, Apogees (now coming back), and the big bass panel Maggies (old and new) I don't know of any panel dipoles (as opposed to cone dipoles) that go flat all the way down to 25 or 30Hz . And as most people eventually discover in the case of Maggies, you really have to play them loud to get them to perform "full range" -- but it IS possible, and they CAN be driven hard without distortion. My Tympani 1-D's had great bass (ie no need for a sub) but only at live levels and they absolutely required a powerful ss amp. If you wanted rich sound otherwise, you needed a sub or a "loudness" control.

Most planar dipoles (ie electrostats) just don't have the enormous panel size it would take to produce low bass -- even the big Soundlabs barely make it, but they do make it!
So with most of them, the bass output (SPL) just starts tapering off at (what would be for an ordinary box floorstander) a fairly high frequency -- beginning 80Hz for my CLS's and down to "you can't hear nuttin' at all" below 40!! BUT, you don't get any bass distortion, no matter how loud you play them.

So fact 1.) The bass response profile (generally) for dipole planars (including Maggies most of the time;--) mimics a typical high-pass rolloff curve that you'd find in a typical electronic crossover set to say 80 or 100 Hz at a slope of 6dB per octave, PLUS there's no phase shift. Knowing that, it sort of makes the use of an external high-pass filter or crossover redundant -- the speaker, BY ITS DESIGN has already rolled off the bass in the most natural way possible! The only way you could get it to distort, and ONLY at the frequencies above its 40Hz lower limit, would be if you tried to correct it's natural bass defficiency by trying to kick it back up with an equalizer.

So fact 2.) All you need to do is add a sub that has a high frequency rolloff curve that's the opposite of the panel's low frequency rolloff curve (in other words, where the SPL of both speakers falls to about half, at the frequency where the curves cross.)

As for why your Maggies sounded better with high pass filtering, with or without a sub -- I don't know, but something was not right -- it was certainly NOT due to an imperfect design. Perhaps it was the amp, or a failure in the crossover, or even a bad panel? I know the folks at Magnepan, and I can tell you they wouldn't put out a product that sounded better after the customer circumcised it.

Fact 3.) Placement: Dipole speakers radiate two waves, equal in strength and opposite in phase. And, there are tons of dipole sub designs, which would be the obvious choice to match with panels. UNFORTUNATELY, there don't seem to be any that are commercially available and/or have great transient response. I found that the new Martin Logan designs (the Depth and Descent) with their omnidirectional radiation pattern can be made to approximate a dipole sub, if placed right between the panels and set to a 90 degree phase angle. (Meaning the sub is only a LITTLE out of phase with the front OR back of the panel.) And, they are FAST! Martin Logan also has brought out the new Summit, which has its own self powered built-in sub each side. They sound great, but I'm not sure they solve the dipole phase-matching issue as well as my solution (one Depth in the center) or perhaps a real dipole sub would do.

As for subs-with-box speakers, that seems to be a two sub solution usually. Whether its by grouping sub towers with mid/high towers (Alon, Genesis, Pipedreams, etc) or with main full-range (?) speakers. The latter being something I just totally don't understand (why not just build decent bass into the main speaker to begin with.) I'm OK with the monitor/sub solution, but again, it's going to be a compromise no matter how it's done (ie one sub or two? and where do you place it/them?)

Basically, my "convictions" (I'm OK with that:--) are that for two channel, keep the system itself as pure and simple as possible, especially the preamp-to-amp-to-speaker part of the system. Think "minimalist". Don't add stuff to fix the signal when you should fix the room. Avoid the urge to bi-amp (unless the speaker comes with it's own bass amp of course.) If your room is smaller than 15.5 feet by 23 feet, accept that your speakers will be on the short wall and you will have to listen "nearfield." As for HT or multi-channel, I have no particular convictions because the object is to produce stunning effects whatever that may require.

Gentlemen,

I'm afraid that I'm becoming confused with the responses to my own question and now find myself even more puzzled than when I started. Considering that I have a great deal of knowledge to assimilate before I can take such technical observations into account, would I be folly to use my pre/pro's bass management to set a crossover at the -3db frequency of my Maggies and slowly turn up the M&K until I can match SPL at the point of crossover? Is this approach too pedestrian for the Magnepans?

I notice an MX-150 Mk II for sale here in the classifieds... I'm beginning to think about picking up a second! Would my money be better spent on the addition of an SMS-1 or some other EQ to smooth out what is an admittedly atrocious room than on a second sub at a good price? I hate the concept of limited resources with limitless wants... thank you, microeconomics, for my crippling indecision!

Rodman99999, I did it that way too (for 14 years, not 26 years) until I realized it was the wrong approach ;--) I sure was happy to eliminate those external filters, delay compensators, etc., from the chain.

If your (very well designed, I assume) planar speakers sound strained, it's certainly not because you're runnuing them full range, it's because your amp is not right for the job. Planar speakers don't "strain" when they run out of bass response, the bass just fades away.

There's absolutely no reason to take ANY bass response away from the main speaker and send it somewhere else. If the main speakers produce crappy bass and it's not the amp's fault, then you should sell them and buy something better.

The purpose of a subwoofer is NOT to take over any bass duties from the main speaker but just to (subtly) fill in those regions where the main can't go.

If you'd like confirmation of this approach, you can speak with Steve Winey at Magnepan and/or Jim Power at Martin Logan. Steve will also tell you that bi-amping the old IV-A's, 3.6's and 20.1's is OK, but only if it's to put a tube amp on the tweeters -- not to cut off the bass response.
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Although most planar speakers aren't capable of the excursion necessary for low bass reproduction(and hence: roll off the bass)- It doesn't mean they aren't trying(not to mention the wasted wattage). The sound of your Maggies will benefit greatly if you use a GOOD high-pass filter(BEFORE your power amp). I've been actively bi-amping planars for the last 26 years, and have found they ALL sound cleaner/less strained/more dynamic with the bottom handled by another amp/sub system. The corner sub not only energizes the room and lays an excellent foundation for your music, but- the driver has much less work to do having the reinforcement of the room boundaries. The drawback is in the time domain. Three feet will add up to a lot of mS in delay. I'm using a TacT 2.2X which delays the mains to compensate(along with a multitude of other neat tricks).

Bob, I made it very clear that my remarks applied to panel speakers, which do not have increasing SPL in the bass and (for this reason) do not exhibit bass distortion since you can't have distortion where you have no response.

The bass response in (almost) all panel speakers (along with the SPL) tends to roll off smoothly starting between 40 and 80 Hz (depending on the speaker) at a slope similar to that found in a high pass crossover circuit anyway.

The object (again, with panels) is NOT to assign bass and mid-bass to two separate devices but rather to BLEND the outputs of the two devices as if they were part of a single enclosure/crossover system. Attenuating (sloping off) the sub starting at 10 to 20 Hz below where the panel initially begins ITS natural roll-off insures a nice flat response across the point where the two speakers' acoustic response overlaps, sort of a "natural" blending (ie in the air) of crossover slopes.

As for locating the sub, the dipole radiation pattern of panels produces sound waves between the front and back of the panel that are at approximately 90 degrees out of phase with the original signal (ie 0 degrees at the front, 180 degrees at the back, 90 degrees in between) so locating a single sub exactly between the speakers F/B/L/R, and adjusting it's phase (if you can) to 90 degrees, will make it virtually disappear and be indistinguishable from the panels.

Again, these comments apply to pure full-range dipole speakers (ie not hybrids with cone drivers as in many Martin Logan speakers.) Examples would be ML CLS's, Maggies, Quad 57's, etc. Soundlabs do qualify, but shouldn't need subs anyway ;--)

Some of your remarks DO apply to typical two or three way monitors or full-range box enclosure speakers; and I have certain other ideas about those applications. I'm quite familiar with M&K bass management system. I know Ken quite well (in fact I designed their logo back in 1970) but his recommendations apply (primarily) to multichannel systems with conventional speakers, LFE processing, etc. I still stand by my advice as to using subs with dipoles.
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That article and M&K's test tones look to be a fantastic resource, Bob. Thank you so much for the response!

-Steve

P.S. One quick question... could placing the sub behind my left 1.6QR cause conflict with the sound radiating from the rear of the panel? There is a good amount of breathing room back there (more than 3'), but I'm not sure what the end result of that interaction would be.

Panel speakers tend not to go very low (ie most Maggies and almost all stats) and therefore they have a natural bass roll-off when run full range. In other words, no need to use any high-pass filters with them to "relieve" them of bass duties.

So run the sub (and its amp -- internal or external) from another pair of preamp main outs (if your preamp has two pair) and set it 10 - 20 Hz below the spec'd low limit of your panel. Then slowly bring up its volume until you can just barely hear the additional low end.

If you're buying just one sub (an excellent solution with panels IMO) place it exactly between the speakers (L/R/F/B) and if it has a phase adjust, set it to 90 degrees.
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