Would a Rythmik still benefit from an MBM?

I currently use Reference Infinity mains that can actually reach down to 27Hz (in-room response) and have an "original" VTF-2 (in 25Hz tune mode) with the 180-watt Class A/B amp and light-mass 10" woofer crossed at 50Hz over to a sealed MBM-12 that's crossed (@ reciever) at 80Hz. Both these subs are co-located and the blend is absolutely seamless. REW shows a relatively flat in-room response down to 21Hz and the bass sounds quick and tight and 'real'. I'm really happy with it currently yet I'm contemplating purchasing a Rythmik 12 (to replace the VTF) to get more extension but I don't want to lose any of the tightness in the mid-bass region or upset that seemless blend. Does anyone have any thoughts on this? Will I need to ditch the MBM? and maybe cross-over higher? keep the MBM and do a direct replacement with the VTF-2? SQ is everything, I don't care about flapping pant legs or vibrating my butt or getting slammed in the chest... I just want it to sound 'real'... so, which will sound better in the critical 50-80Hz region? My Infinities sound great in that region (better than the MBM even) but I really want to unburden the 10" IMG woofers in them to allow the best reproduction in the 80-200Hz range without interference from the lower freqs... and use the 350-watt MBM to bring those mid-bass freqs 'forward'. How will things change with a Rythmik 12? Thoughts?

In terms of headroom and output, the system would probably benefit with the sealed MBM-12(sealed and tweaked by Hsu?), but for sound quality am not so sure.

It would definitely be interesting to compare.

Nothing much to add to Curtis's thoughts.

Things shouldn't really change for you. I don't see why you couldn't use the Rythmik as a drop in replacement for the VTF-2. You should be able to achieve the same type of blend with the MBM and Rythmik that you enjoy with your MBM and VTF-2. Also, you have the luxury of being able to try things without the MBM at all, since you seem to indicate that the Infinity produces better mid-bass quality than the MBM. You could try crossing over the Infinities to the Rythmik at 50hz as well.

This reply is based on using a pair of Rythmik F15's co-located with my Dayton Audio UA721 MTM main speakers and crossed over at 80 Hz. The reason for the MBM unit in the Hsu line is that while ported designs can provide lots of low bass output in a relatively small box, the tuning needed to accomplish that can detract from accurate mid-bass. The MBM fills in a tuning "hole" and smooths the response. Rythmik subs do not suffer from tuning anomalies, so do not need any help accurately reproducing the entire bass region. My F15's are superb with music. This is particularly noted with percussion (large drums of various types) and bass guitar where the sounds are known to be in the frequency range of interest. The lowest notes of piano and synthesizer are equally impressive, although without disconnecting my mains it's not readily apparent which speakers are producing which tones. I can not imagine an MBM would provide any improvement. However, since you have one already, it certainly wouldn't hurt to try it with your Rythmik sub and satisfy for yourself whether there's anything to be gained by using the MBM.

Bill

All very interesting comments. Its funny but whenever anyone asks a question often without realizing it they are actually expecting a certain answer in response to the question. In my case I guess I was hoping someone who would read my posting might have actually had some experience with an MBM and therefore had first-hand knowledge of its capabilities in relation to a Rythmik. It appears the MBM is still a rare animal in subwoofer circles. So I guess I must be the first here to compare and contrast a Rythmik in the mid-bass region (my definition: 50-80Hz) to the MBM. Yes, it is a HSU modified sealed MBM12 and suppose to be the very last one they had... at the time it was being used for benchmarking I believe.

Since I intend to use my Onkyo for the bass management and the HSU its replacing is only a 10" and a 180-watter, I assumed the standard 300-watt amp should suffice. Since Ascend doesn't seem to offer Rythmik subs with the standard amp option I had to go directly to the Rythmik site. After conversing with Brian my thoughts were to get the F15 but unfortunately they are out of stock in Black Oak until second week in August. In this particular instance, time is an important factor for me (I'm scheduled for an impending operation early August) so I went with the F12 as originally planned. When it gets here I will try all combinations to see what works best for my situation.

Anyway, thanks to all for your thoughts in this thread. Appreciated it.

I have heard the MBM-12 on a few occasions, but have not compared it to my Rythmik.

I was just curious why you are still going to run the MBM if you feel the Infinity speakers sound better in that region anyway? Headroom? Impact?

In my opinion, if you have a very capable subwoofer (Rythmik is I am sure) that has good mid bass slam AND is enough subwoofer for your room, there is no need for the MBM :D

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Originally Posted by vantagesc

I was just curious why you are still going to run the MBM if you feel the Infinity speakers sound better in that region anyway? Headroom? Impact?

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A good question which I actually tried to address earlier. The Infinities are a 4-way speaker design with the 10" woofer crossed-over at 200Hz... this would then have that one speaker handling all freqs from 200Hz down to the 27Hz in-room response. I believe that if a speaker cone is having to move to reproduce a 30Hz tone then that large cone movement must be affecting its ability to simultaneously reproduce say a 100Hz or even a 200Hz tone cleanly. If I were to unburden that woofer of having to reproduce the most worrysome freqs that require the most cone excursion (those freqs below 80Hz) that would allow it to dedicate its cone movements to accurately reproducing the 80-200Hz range with less distortion and thus more accuracy. However, just recently I tried dialing down the subwoofer channel by 3dBs and turned on the 'Double Bass' feature on my Onkyo, where both Infinities and sub(s) are fed the same bass signal (sans the LFE), and it has improved bass response without a doubt... so maybe my Infinities don't really need the MBM. One thing that I do like about the MBM is the 350-watt amp... it provides more headroom for the Onkyo and allows me to bring the mid-bass 50-80Hz freq range 'forward'.

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Originally Posted by Gov

In my opinion, if you have a very capable subwoofer (Rythmik is I am sure) that has good mid bass slam AND is enough subwoofer for your room, there is no need for the MBM :D

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This is what I need to find out. I don't really care about 'mid-bass slam', what I'm after is 'mid-bass accuracy'. My past experiences have only been with conventional ported subs and my subjective impression has been that subs capable of ultra-low freq at high SPLs and acceptable distortion levels typically do not sound very accurate and tight when reproducing mid-bass freqs. It appears to be a trade-off made in driver materials and construction that allows very large cone excursions without physically distorting at the expense of light, quick and accurate response during the small excursions. An example might be the GR paper cone option for the Rythmik F12... its lighter construction reportedly makes its response more nuanced for the higher freqs but less capable of resisting cone distortion at the lower freqs at high SPLs. The main reason HSU created the MBM was to use a lighter paper cone driver that didn't require large excursion capability (since the speaker design is meant to roll-off at 50Hz) and thus it could use smaller, lighter and more flexible surrounds, this makes it more nimble at reproducing the mid-bass freqs... in contrast to the type drivers employed in most true subwoofers. Seems most people missed that part about the MBM's driver advantage and only focused on Dr HSU's suggested near-field application for the ported MBM, which is why simply placing any uber-subwoofer near-field doesn't really get you the same type of mid-bass response as actually using an MBM... plus you have now introduced the possibility for time delay alignment issues with the 'other' (true) sub. My sealed MBM is not, nor does it need to be, located near-field, which is one of the reasons why I have no phasing (time delay alignment) issues and is a major reason why the blend with the VTF is so smooth and transparent. I believe the reason my Infinities sound even 'better' (to be read as 'more nuanced') than the MBM is because the 10" IMG polypropylene cone woofers used are both smaller and lighter still than the 12" woofer used in the MBM... and the older surrounds appear to be both thinner and more flexible. I want accurate, tight, nuanced mid-bass response with deep extension capabilities from a sub... so, can a single sub do better than two dedicated subs, each tailored to best reproduce different ends of the bass freq range? (Not unlike the concept of a 3-way speaker arrangement sounding better than using a single full-range driver.) Maybe a sealed sub doesn't have these issues?... maybe its not an issue with a direct-servo sub?... I don't know but I will very soon be able to judge these things for myself. I requested the sub (F12 w/ standard 300-watt amp) be delivered next Thursday and so I think I should know a lot more by next weekend.

Just wondering, what frequencies would be encompassed by the term "mid bass" in relation to subs?

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Originally Posted by jbjb

Just wondering, what frequencies would be encompassed by the term "mid bass" in relation to subs?

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Ah, such a simple question but alas the answer is not really well defined. There have been whole threads over on the AVSForum dedicated to arguing over what exact freq range does mid-bass refer to. Car audio guys give a totally different range than home audio guys, and audiophiles and trained musicians seem to have different ideas than home theater aficionados. So take this with a grain of salt but when I use the term in relation to subwoofers I'm thinking along the lines of a 40-80Hz range... its the freq range that is often credited with providing the "slam" or visceral effects of bass when played loudly.

Thanks for your thoughts on what mid bass means. In terms of "slam" I always thought the area between 30-50Hz was key.

So then what is the role of the deep bass like 15-30Hz?

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Originally Posted by jbjb

Thanks for your thoughts on what mid bass means. In terms of "slam" I always thought the area between 30-50Hz was key.

So then what is the role of the deep bass like 15-30Hz?

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The precise freq range for "slam" has also been highly debated (again there are threads on other forums dedicated just to arguing the point).
My MBM is tuned to roll-off below 50Hz and I have it crossed at 80Hz. If I want "slam" all I have to do is turn it up and you can literally feel the bass passing through your body. However that upsets the balance of bass... it's great for a thrill ride but more often a bit too juvenile for my tastes. My tastes appear more oriented to seeking a musical balance across the whole freq spectrum with the bottomline of having things sound REAL as opposed to just pursuing giggles. Deep bass (below 30Hz) is for making pant legs flap and vibrating the foundations of your house and pissing-off your neighbors.... seriously, deep bass is for movie explosions, UFO landings, monster stomps, earthquakes and other such movie sound effects. For me, above 30Hz is for musical instruments and voices... however I will admit that with certain movie sound effects, unnaturally boosting the mid-bass region can be fun by making you jump at the sound of gunfire and vibrating certain parts of your body. I wish Rythmik subs would have the damping on a remote control so I could change the tuning just for those 'fun' movies.

Just a quick follow-up...
After living with these subs in various configurations for awhile I've got to say, for me, I feel the answer to my original question is "Yes, a Rythmik will still benefit from the addition of an MBM". I purchased a second Rythmik two weeks ago as I love what it does below 50Hz, its just amazing how accurate and clear those low frequencies can sound coming from these direct-servos but alas I prefer having the (sealed) MBM punch above 50Hz. The good news is I find the blend is completely seamless between the MBM and the Rythmiks and I believe I now have the best of everything from 80Hz on down... with the goal here being 'keeping it REAL'.

How did you install your two Rythmiks and your MBM?

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Originally Posted by Mcpanse

How did you install your two Rythmiks and your MBM?

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Not sure what kind of answer you're looking for here but...
The short story is... After a LOT of attempts at different configurations I finally found a good blend by literally replacing the VTF-2 with one of the Rythmiks. IOWs, I have one F12 co-located with the MBM. This F12 has its cross-over set to what approximates a 40Hz on the dial. The two are stacked in totem-pole fashion about a foot to the inside of and slightly behind the left main and the other F12 is located in the mirrored position in relation to the right main and its XO is at max (IOWs the Onkyo controls the bass management). This arrangement makes phasing equidistant to all listening positions for all three subs. My room is almost but not quite exactly symmetrical, which is why I think this arrangement seems to work out so well. I had to level balance the F12 / MBM in relation to each other first and then balance that combo to the other F12... BTW none of this was easy to do. In the end, it does sound great... However I would feel better if I had another MBM to co-locate with the other F12 and then I could also drop its XO to 40Hz... to be honest, I just don't want to pay the full price for another MBM right now, so I'm patiently waiting for a used sealed MBM to come up for sale somewhere (or if I can find a really cheap ported version I'd pay the additional $70 to ship and get the amp modified). Right now time is on my side as I'm really quite happy with the way everything is sounding ...so I'm feeling like I can afford to be patient and wait for a good deal on a used MBM to turn up.

Thanks Monomer. A very useful post for folks who might want to go this route.

Did you connect the MBM to the F12's line outs, or visa versa? How did you handle the crossover settings? That's what I was getting at with my question above. Sorry for the confusion.

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Originally Posted by Mcpanse

...Did you connect the MBM to the F12's line outs, or visa versa? How did you handle the crossover settings? That's what I was getting at with my question above. Sorry for the confusion.

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I used lotsa splitters to go from the single sub pre-out on my receiver to feeding each sub's inputs (both L and R). The MBM has a natural roll-off below 50Hz so the Onkyo handles the bass management on the upper end (I'm using 80Hz at the Onkyo)... so the challenge becomes setting the F12's XO appropriately. I should have used REW to help but instead I just used test tones and a SPL meter to find the XO point that produced a relatively flat transition from ~30-60Hz and it happened to end up being with a XO setting approximately corresponding to 40Hz on the dial. I guess that sounds right since XOs are not brick walls but slopes and when you sum the output of two slopes together you're better off measuring the total SPL output to prevent unnatural peaks at the XO point. Anyway, that's what I've done so far. In the near future when I get the time I will probably break out REW and fine tune the whole set-up but for now, its sounding really good.

Latest iteration (for the last month now) has both my F12s crossed ~40Hz and using the single MBM to handle the mid-bass range solo. This time I employed REW to select a cross-over point that provides a smooth transition with the MBM's roll-off and also used it to help set the X-O points identical between the two Rythmiks. I'm nearly to the point of breaking down and purchasing another MBM to co-locate with the other F12, even though currently the sound is well-balanced and FR reasonably flat with adequate headroom... (I guess must be the money is just burning a hole in my pocket).

have you compared the SPL freq. range independently for each piece in your system from your listening position and their destined location? just because your mains go to 27hz doesn't mean that you should run them down that low, or maybe i misread that OP

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Originally Posted by scape

have you compared the SPL freq. range independently for each piece in your system from your listening position and their destined location? just because your mains go to 27hz doesn't mean that you should run them down that low, or maybe i misread that OP

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Thanks for the response. I'm actually getting ready to go off to the beach with my dogs but it just so happens I added a 125"-long corner bass trap (a ceiling/wall junction) and 'fiddled' with the Rythmiks' cross-overs (while verifying the results with REW). I use Audyssey multEQ because my aim is to get the best overall balanced FRs at each of the 8 seating positions in my theater. If I chose to use a BFD to dial in a single listening position I can get it dead flat but unfortunately at the expense of a decent FR at the other seating positions. So the graphs I've attached come from sitting in the middle-right rear listening position and though the FR varies from one position to the next (greatest is between front row seats and back row seats) they all are comparable smoothness-wise. The dip at 30Hz is everywhere and nothing I do can remove it so I figure it must be a room mode... the broader dip at 85Hz-110Hz is more position related and is a trade-off to compensate for a smoother response at other seating positions. The bump ~50Hz I reduced some by lowering the Rythmiks' cross-over but unfortunately that also seemed to lower the 30Hz dip as well, so it too is a result of a compromise and will remain about where it is. (BTW, no form of octave smoothing was used on those graphs below) These graphs were created while running both Rythmiks, the MBM. and both Infinity mains with an Onkyo providing bass management cross-over from MBM to mains at 80Hz and the Rythmiks' own cross-overs dialed-in at somewhere around ~45Hz to compensate for the MBM's natural roll-off below 50Hz. The whole bass frequency region sounds just great from any listening location. I need to now work on the above 300Hz in-room frequency response...

Anyway I'm now off to the beach and will 'fiddle' some more over the long Thanksgiving weekend... that's when I'm also planning on building two rather large QRD diffusors (4'X3') for the back of the room (targeting the 350Hz-4500Hz range because of some troublesome deep combing) and am also going to be building a rather large absorber (4'X8'X4") to cover the first reflection points on the ceiling up front... I suspect it might have a small effect in taming the upper mid-bass region but I'm really trying to target the higher-frequencies with these additions due to the unforgiving nature of the two and a half cement block walls and poured concrete flooring of my listening space (its a basement theater) and the resulting acoustical challenges they present for me.

And yet another update... (actually the final up-date)
The large QRD diffusor I placed at the back of the room... bummer, didn't seem to improve the higher freq combing by much as I had hoped... the thing weighs ~180lbs!!!
The large broadband absorber panel on the ceiling actually caused an unintentional dip in the 200-400Hz FR range, 'nuther bummer. However its all still a work in progress. (Its not all bad... Reverberation time is reduced and the sound is quite tight and sounding very well defined, that's a good thing)

Ah, now about the bass end of things... I've decided after much music listening (music is a great love of mine and so I do a lot of it) to leave the mid-bass to the Infinity mains as they really do sound the closest to "real" plus I'm blessed in that the mains' best positions for imaging also happen to work quite well together for the bass freqs at all the listening positions (meaning no moderate or serious nulls are created). Therefore after judging through lengthy sessions of critical listening and then verified with REW readings, I've settled on simply removing the MBM entirely from the system and using the AVR to cross-over from the mains ~50Hz and letting the Rythmiks take it on down into the sub-sonic frequencies. This is probably the best sounding bass I've ever experienced in any room, so now I'm back to working on the in-room response at higher frequencies .

So to bring this topic full-circle I will now say the answer to my original question is "No" I don't need an MBM because my large Infinities actually sound better and as luck would have it, provide for a smoother in-room freq response. I no longer have that little extra kick for movies in the 50-80Hz range that the MBM gave me but then the increased definition and nuance of the Infinity woofers makes for a sound that's closer to "real" which is actually "the sound" I am after.

My experience here won't necessarily apply for everyone else (maybe not even anyone else) but because of what I'm running for my mains and the fortuitous balance of the mid-bass being exactly the same location as best imaging from the mains, it happens to work out for me. So it appears to have taken me about 5 months after purchasing my first Rythmik to finally settle the original question but based upon my past experiences dialing-in audio componets I'd say that's about par for me.

Guess that's it for this thread, unless someone has any questions or comments to add I will move on and let this thread slowly sink to the bottom.

that's good that it's resolved to your liking. in the past after reading up, I realized letting my avr do all the xover work was important, and just easier haha. I have a denon and it tries its best to make things work for the room I have it in; but I'll be darned with the setup. not only is my sub a bit lackluster (if you rated a HTIB sub as 1-2, and a highend 1000$ sub as 8-9, i'd fall in under 4-6 I'd say, depending on the placement) but the whole layout I have it currently setup in is just plain terrible, but what am I to do as I am in a temporary situation and it is not my room. which sucks b/c my last place was all to my own and the whole living room was situated around my speakers haha. ultimately I ended up running 3 channel + sub for my music, just b/c it ends up sounding a heck of a lot better.
I guess the whole point to bumping this thread is simply that I like that you found where you are comfortable with the setup, and I think that's really important. b/c you could tweak this crap all year long and may never find your 'perfection'.