[Skynyrd]

Warner,

I think you're on to something!  The two woofers in an RM40 are manufactured differently--different magnetization.  So the woofers are different--but the signal from the crossover is the same.

Your tireless recommendation of the Behringer equalizer is a breath of fresh air!  I've just got too many other things on my financial/hobby plates right now.  Otherwise I'd have the CDWG, two brand new and affordable Behringer units (DEQ2496 and the DCX2496 crossover) that I'd be having a devil of a time figuring out how to work, and an extra couple of amplifiers for my NHT woofers.

First, the bathroom floor must be rebuilt, including many added joists, but not if I keep posting to this darn board!
Skynyrd

[ctviggen]

Certainly the passive radiator is going to cause a roll off at a certain point (definable at least in part by the putty).  I'm interested to know whether these really are three ways or not, as I may go active.  Four ways means yet another amplifier.

[James Romeyn]

As many know I worked at VMPS & am familiar with the crossover design.  Crossover-wise all 30s & 40s are very similar, both having a sum total three electrical splits via the crossover.

All RM30's are split into two major divisions as follows, identified by the suffix:  

"C" is for center channel.  Besides the down-firing passive radiators, the C has only the front firing drivers & no others.  With all due respect to VMPS, I personally find this moniker very misleading, because all the following audiophiles are better served by this version: Those with a sub, those wanting to minimize offense to neighbors or housemates, those with high sensitivity to cabinet vibration & wanting it minimized.

"M" is for Megawoofer, with one additional 10" side-firing driver.  Bass output is increased, but there is little to no appreciable effect on the lowbass cutoff frequency.

With all the above speakers, RM30C, RM30M, & all RM40, there is a sum total of one crossover split comprising the lowpass crossover of all woofers, no more, no less.  On the RM30M, on the top end of the woofers, the 10" has a much lower resonance vs. the 6.5's.  Naturally the 10" rolls off earlier/lower than the 6.5's.  

On all RM40's, the 10s look identical externally, both even having the same diameter voice coil if memory serves correctly.  But the lower 10" is a Megawoofer with double-magnet (80 oz) motor, the upper 10" is the standard single 40 oz magnet variety.  In this case, similar to the RM30M, the double-magnet has a lower resonance & its top end naturally rolls off earlier/lower than the single-magnet 10".  

BTW, on my 40s I found better sound by inverting the positions of the MW & standard woofer (lowbass on top, midbass below).  It's more difficult to perform this mod than it sounds.  Go way back & read the threads on it.  

I believe the standard 40s, with midbass on top, had too much midrange reflecting from my undamped 8' ceiling.  Moving the midbass down allowed the heavily padded carpet to absorb & minimize midrange reflections.  Also the reflection pathlength is shortened to frequencies that are above the midbass' passband.  For this reason, even if the floor is hard & reflective, the modification may still improve the sound.  

The 6.5's on the 30s may go higher than the 10" midbass of the RM40.  For this reason, & as a general rule, it is probably better for any speaker to damp the floor in the area directly IFO of the speakers.

[meilankev]

John,

I own RM40s, and they serve double-duty as my 2-channel speakers and the mains for my main Home Theater system.  I use no subwoofer in this system (although I do use one in my Thiel-based "second system" downstairs).  My daughter's system also uses a subwoofer.

Although I have no interest in adding a subwoofer in my main system, I am not delusional, thinking that my system doles out all the impact that is available in the lowest registers.  I absolutely agree that a subwoofer (or two) could benefit the deep-bass performance of the DVD experience.  

And after hearing a couple of well-designed IB subs, I wonder why anyone would ever buy a stand-alone sub these days (if their room can accomodate an IB).

But for me, music is my obsession, which my running the RM40s full-range is just fine.  And actually, the kinds of movies I really enjoy aren't likely to contain a lot of LFE info anyway.

Good luck in your decision!!!
Kevin

[ctviggen]

BTW, on my 40s I found better sound by inverting the positions of the MW & standard woofer (lowbass on top, midbass below). It's more difficult to perform this mod than it sounds. Go way back & read the threads on it.

I've been thinking of doing this for a while now.  Any ideas on what the threads might be entitled?  

So, if I go active (say with DEQX), I'd need three amps or four?  I think three, one for tweeter, one for mids, and one for bass/low bass.

[ctviggen]

I should say that I'll be taking the RM40s apart to add BH5 and will examine the crossovers/change midbass/bass then.

[woodsyi]

It's three way in terms of passive filters but 4 way acoustically due to different woofer outputs. Like Warner said, both woofers see the same signal -- they roll off differently.

[ctviggen]

Coolness.  So I can use one amp to drive both bass and midbass (and "rip out" the crossover to be driving via a digital filter).

[Skynyrd]

Jim,

Thanks for your insights on the RM40's!

Here's what I think I hear:  Very similar sounds coming out of the top and bottom woofers in the RM40's. Just driving the woofers with the stock crossover.  (This is not much fun to listen to)

  I've got the newest "megawoofer" on top--so both of these RM40 woofers have double magnets, the top being of an alledgedly different magnetization than the bottom, a difference that affects the resonant frequency of the woofers, this done to avoid booming.  Or so I've read here!

Am I saying you were in placebo-land when you switched your woofers top to bottom?  Well, I wasn't there, and I'll take you at your word.  

  I like a sugar pill just as much as the next audiophile--especially when it is free!!  


Skynyrd

[James Romeyn]

I wish it was free, it was much more a pain in the u'n ow ut to reverse the woofers.  

My room has major modal problems.  I paid dearly for a professional engineer to prescribe acoustic treatment remedies, & am in the process of doing the upgrades now.

When I had the 40s I had very little treatments.  Meaning the modes & reflections were a worse problem at that time, which may well have affected the outcome swapping the woofers.  Other than the time & probable need for replacement gasket tape to seal the woofers, you have nothing to loose to try swapping them.  But do find the thread & read my instructions, there are more details than you'd imagine.  

Since then I built a huge corner trap, & that helped a lot.  Also since then, I got a sub with continuous infinite EQ, providing very flat bass.  The VMPS sub & amp are superb value, with a nice one-band parametric eq to flatten your worst bass mode.  With a HT receiver or pre-pro, the xo's between the sub & mains can be staggered to minimize or eliminate a second higher frequency mode.

BTW, the OEM passive midrange high-pass crossover has two first order poles in series, the lower one around 100 Hz, the higher around 260 Hz.  The mids also have a low-pass first order pole around 6.9 kHz (its acoustic first order rolloff starts around 10 kHz).  The tweeter has one 12 dB pole around 7 kHz.  Keep this in mind if you decide to go fully active.  Replacating all passive OEM xo's with similar active poles may require a sum total three bands for the mids alone: 2 series high-pass, one low-pass.  (Bass & treble one pole each, sum total five poles for each speaker.)  Of course you could mix passive & active poles, but why bother unless you go all the way & do it right.    

I'd personally not even try any slopes or poles other than OEM.  In other words, I'd spend time only trying to replace the function of the passive OEM xo's with the active digital or analog crossover.  

I would absolutely love to hear RM30's crossed fully active as per above.  You'd absolutely need gain controls on the bass & treble.  A gain control is unecessary on the midrange, the most critical of the three ranges (more mids = less bass/treble & vice-versa).  

Favorite amps for each range: Bruce Moore 50W or 100W tubes on the mids, great 11W to 22W SET tube for the treble, any great 400W SS amp for the midbass 6.5's.  Ummmmm.

[John Casler]

I should say that I'll be taking the RM40s apart to add BH5 and will examine the crossovers/change midbass/bass then.

The RM40 is a 3 way system as Jim describes it, with the MidBass 10", the Low Bass 10" and the PR all part of the Bass System.

Each driver covers a slightly different frequency range, combining to provide the bass region of that speaker.

Great description; Thanks Jim!

Regarding the "swapping" of the Low Bass 10" with the MidBass 10", you need to know what the total effect of performing the swap is.

You need to look at your goals and what your room and system need.

Jim mentions his 8' ceiling and ceiling reflections.  Swapping if this is a problem makes sense, but do know that moving the Low Bass Driver to the top will also drop "boundary gain" of the low bass.  I think Brian has said he would estimate this at an additional -3dB down at 24Hz.

The low bass might be affected even more by loosing the "joint effort" effect of the Low Bass Driver working with the Passive Radiator.  This increases the effectiveness of the PR.

So if the RM40 is your sole Low Bass speaker, and that is already low due to room problems, then swapping the woofers might make "that" worse.

If you wish to retain, your low bass, an alternative is the "Sonic Director" tweak which also works well for low ceilings.

Or if you opt to swap, make sure you have a sub in place and swap away.

While I haven't tried it myself, I have had a client report an excellent result by re-installing his Passive Radiator slot "backwards" so that it was "REAR FIRING" rather than front, which changed the bass path in his room and he found it helped with some room problems.

If do the swap and have a low ceiling, and a close wall posistion, you might try the "rear firing" slot and find the results interesting too.

Make sure and use "tweaks and changes" that fit your goals, room and system, for the best result.

[ctviggen]

Interesting part about the rear firing slot -- I thought about that too.  I find the low bass tends to get "lost" on the RM40s.  I'm thinking this is partially due to the bass driver physically being low.  It would be interesting to lift the speaker just to see what happens.  Also, I think whenever a bass driver is near a boundary, you're bound to excite modes you might not want to excite.  I know that moving my VMPS Larger off the floor really helped the bass response, but that may also be due to the AVS bass traps.  Thus, my quest to increase low bass response (assuming I don't get the Largers working or don't want to use them; if they're working, this is all a moot point).  I think the mid-bass response is more than fine.  So, I'd rather sway mid-bass for bass.

[James Romeyn]

Re. RM40, try this: Switch off or disconnect the ribbons & listen only to the bass.  Get closer to the regular midbass driver & listen to how high up it extends.  I think this much midrange sited so close to any normal 8' ceiling may be asking for trouble, but that's only my opinion.  I generally favor first order slopes, as do other top brands besides VMPS.  But one of its drawbacks is high-reflectivity in cases exactly as described here.    

My room has/had a huge mode around 30 Hz, & moving the RM40 MW up may have alleviated that problem as John suggests.  But I'm not nearly as sure as John &/or Brian.  I think the following, expressed in many technical reports by engineers, is accurate.  

In a reflex system, the lowest output is produced almost exclusively by the port, or in this case, PR.  The PR mass simply replaces the mass of air in a port.  

So, if the RM40 cuts off -3 dB at 25 Hz, the active 10" MW's contribution at cutoff is almost nill.  The MW is sharply filitered below the high-30 to low-40 Hz range.  The ENTIRE SYSTEM working together (cabinet, air volume, stuffing, PR mass & spring, two active 10" woofers) produces the output at cutoff, but the MW's actual physical movement at cutoff is nill.  The PR moves virtually all the air at cutoff & for about .5 to .75 octave above cutoff.  

You need only one below-average eye to confirm this: Play a 25 Hz test tone.  Compare the stroke of the MW & the PR.  The PR stroke is about 8x the MW.  That my friend is more output, of the very large quantity variety.  If you don't believe your eyes, measure with a meter at the same distance for the PR & MW, but only at cutoff & immediately above.
 
The MW's low-end output is so sharply filtered because it is severely damped by the PR mass, which vibrates 180 degrees anti-phase with the active drivers.  Remember the port or PR mass is driven by the rear output of the active drivers, not the forward output.  By its very nature it must be anti-phase.  Reflex works because the ear has minimal phase sensitivity at these frequencies & again, their output overlaps only minutely.  (BTW, if you have clear simultaneous view of a PR & active driver, while playing a very low frequency tone you should be able to see the drivers' anti-phase characteristics.  As one pumps, the other vacuums.)

My point is, regarding the boundary coupling, swapping woofers might affect midbass & up, but absolutely not the output at cutoff & immediately above, as alleged by Brian.

Lastly, regarding the alleged affect of coupling between the PR & MW.  The wavelengths are so long below 50 Hz that the spacing itself should have zero effect.  But the 4.5 extra feet of internal fiberglass damping might be a secondary effect causing the -3 dB sited by VMPS at cutoff.  

I'm certainly open to correction on all these matters.

[ekovalsky]

Skynyrd,

Thanks for the info.  Then I will probably get a pair of RM30s and a sub.  Is there a link to Ekovalsky's measurement of the RM/Xs?

Thanks.

Measurements were made with TacT RCS 2.2X and S2150 amps (150/300w into 8/4ohms) in passive biamp mode with RM/X.  Yellow & orange traces show the mid/tweeter response, blue & purple traces show the woofer response.  Note the node at 40hz (predictable from my room dimensions) and absence of usable bass below that.  Mic was at listening position about 4m from speakers.  Speakers were positioned very close to the wall which enforced bass response at the expense of imaging/soundstage -- further out into the room the bass response was reduced even more.

http://members.cox.net/ekovalsky/msr_vmps.jpg

Now for comparison here is the graph of my current speakers, measured with the exact same equipment in the same room at the same distance.  Important to realize these are a big two piece per side system, with dedicated subwoofer towers and separate main channels designed to run without low bass.   Even used these were much more costly than the RM/X; nonethless I am very pleased with their value/performance.  I have the mains and subs crossed at 63hz with 36dB/octave high and low pass L-R type filters -- see crossing purple traces.  [During measurement, the crossovers are not enabled thus the sub has output extending beyond 400hz.  During listening, the sub 42dB down at 126hz.]

http://members.cox.net/ekovalsky/msr_alon.jpg

You can clearly make out the two major room nodes (~40hz and ~80hz) and a prominent room dip (~56hz) between them.  Below 40hz there is usable bass response to well below 20hz.  My subjective assessment parallels the measurements -- the VMPS RM/X speakers had essentially no first octave bass response in my room despite the 10" and 12" active drivers, and 12" passive radiator.  Adjusting the mass loading of the passive radiator made no difference in measurements even with large goops of putty added or removed.  On the other hand, the bass support of the Alon system is nothing short of spectacular (in my opinion).  While maintaining great tightness and speed, there is unlimited extension and power for clothes-flapping, house-shaking action!

If you go the VMPS route, I believe true full range performance absolutely requires subwoofers.  For a lot of music, the absent bottom octave won't be terribly missed.  But other music simply cannot be appreciated without it.

For home theater / LFE, subwoofers should be considered mandatory.

[CornellAlum]

It isn't the drivers Eric...

[James Romeyn]

I'd bet money (not much though) that the X would have a lower f3 without the 10" midbass, & with a sum total one active driver, being the 12" MW (Overall bass sensitivity would be lower, but biamping would cure that problem, & most X owners do biamp.)  Reason being the interior air volume is too small to accomodate two active drivers, partly because the mids' lowrange cutoff requires a large subenclosure, decreasing main cavity volume.  The other reason is the swooshes around the mids, further decreasing main cavity volume.  A smaller than ideal air volume increases the Q, & that in turn moves the f3 up, as witnessed in the graph.  I don't know the effect removing the 10" would have on the bass/mid transition; the RM2 works well with the same drivers.  

The problem with the X's f3 performance is that the $2k VMPS ST/R from the mid-'80's (add for inflation) had strong output around 20 Hz (though far less resolution).  That speaker moved my huge mass around on the couch & flapped pant legs like it was going out of style.  

A similar problem exists with the RM30M.  Adding the MW increases lowbass output, but does not apparently lower the f3, again because the too small air volume moves the Q & f3 up (no swooshes though).  But the RM30C-CDWG is the best speaker bargain extant IMO.  Pairing it with a sub makes great sense.  Any sub increases bass output.  The right one will achieve true 20 Hz f3 with high power & low distortion.  

An RM30C-CDWG & sub is a formidable system not easily outclassed regardless of cost.  As reported earlier, one THE Show attendee in the industry said it's the best available below $10k, then thought about the landscape at $10k & immediately upped the ante to $15k.  That person is a Genesis dealer & very familiar with the best available, cost no object gear.        

Though the technique has been around for some time, corner loading a properly EQ'd sub has advantages that are just now being properly publicized.  It has exclusive & highly valued advantages, the most impotant being virtually no primary output (all output is boundary-sourced).  Read the TacT Audio 2.2X corner-woofer system review in 1/06 TAS.  Only my opinion, & YMMV.

PS: The above air cavity dilema is one reason I believe it is at least worth experimenting with eliminating the slot.  The slot & base that comprises it unnecesarily reduce internal volume.  Not a lot, but a littel might make a difference in these two systems.  Reflex systems are far more sensitive to cavity volume that sealed systems.  I realize the slot is a VMPS trademark, & old traditions die hard.  Also the 90 degree turn may filter high-frequency hash from the PR.  But a physics PhD I know states there are good reasons to side-fire a PR.  I've built such systems with good results.

[ekovalsky]

Though the technique has been around for some time, corner loading a properly EQ'd sub has advantages that are just now being properly publicized. It has exclusive & highly valued advantages, the most impotant being virtually no primary output (all output is boundary-sourced). Read the TacT Audio 2.2X corner-woofer system review in 1/06 TAS. Only my opinion, & YMMV.

This does work great.  Big advantage is the increased sensitivity of the corner loaded sub, and also the minimized time delay between bass coming directly from the driver and reflected off the front and side walls.  My sub towers are in the corners -- DSP easily takes care of modes which are maximally excited in this position.  TacT actually recommends corner woofers, rather than just subwoofers.  Some users cross up to 500hz!

By the way Jim, I remember auditioning the SuperTower IIa/R and many years later the SuperTower III at Dynamic Sound in Washington DC.  Lucius had them in a nice big room and there was plenty of first octave bass.  The newer designs seem to have higher F3's.

It isn't the drivers Eric...

Of course not.  Perceived and measurable bass is a complex function of the drivers, cabinet, and room.  As one would expect, the passive first order crossover on the woofer had no effect on the bass extension -- measurements were the same when using the factory crossover or bypassing it for DSP.

[warnerwh]

Jim: The current model RM 40's now have an 80 ounce magnet on the midwoofer also. The magnet is only charged 90%.  This happened at the time the crossover was moved to 280hz.

[James Romeyn]

Warner
Tell us the RM40 difference when the 40 oz 10" was swapped for the 80 oz.  I'm very interested if no one else is.

[James Romeyn]

Eric
I also read in TAS the reports of excellent results at what would likely be thought of as ridiculously elevated crossover frequencies.  

When I first heard & read about corner loading I thought it was useless marketing hash, as so much is ("Perfect Sound Forever" in '79).  Now I'm a true believer.  I don't consider any single fullrange box ideal, regardless what it is.  My current opinion of sub/satellites is exactly 180 degrees inverse of my earlier thoughts.  I prefer my current system, especially in a room with modal problems, over the X, which I've heard several times.  You can add EQ correction to the X's bass, but if you corner load them the mid-treble is ruined.