VMPS Super Towers/R For Sale

Shear Bliss · « **Reply #40 on:** 21 Sep 2013, 04:54 pm »

To ST86
Finally somebody who gets my plight!!! Early versions have too narrow of a slot to adjust mass without laying down. Seriously been thinking about adding three 2" slats on both sub bases, glued an screwed in place. Just buy longer screws and paint.

Not cutting my boxes up but willing to modify them sub bases. Also trying to source the top firing Piezo Tweeters here in the US has gone nowhere. Did find a match online but in a foreign language and could go no further, see pic.

DW

ST86 · « **Reply #41 on:** 22 Sep 2013, 01:45 am »

Yes, I have thought about making a base with a larger slot but figured altering the dimensions of the slot would affect how the passive works. I suppose I could just make a taller base and listen to find out. So many projects, so little time....

Still have the build instructions and schematic for my ST/R, will check if there is any model info about the particular piezo in mine. Been a long time but the one in the picture doesn't look familiar. I seem to remember Brian saying the piezo in the Supertowers was discontinued. Mine are attached to the cabinet with super glue, I would probably destroy them if I was to try removing them to replace them. It is unusual for a piezo to go bad. Did you check to make sure the problem isn't related to connections or wiring? The L-pad in one of the rear terminal cups connects to the piezo, that would be a good place to start.

Ed

James Romeyn · « **Reply #42 on:** 22 Sep 2013, 02:35 am »

I agree, piezo's generally don't fail. The piezo is parallel with the (non) ribbon (it's a planar) tweeter, so if the L-pad is at fault the planar is also dead.

The piezo is parallel with the planar.

Description of top piezo mechanical coupling: A short (about 1-2") long black PVC pipe is loose. The cabinet shop wraps speaker cloth around one open end, then stuffs the PVC into the hole in the cabinet from the inside. It's a simple press fit, no adhesive. This is the state when we received the cabinets oh so many years ago.

I epoxy passives, clean up, or assemble required drivers while Brian and I banter about the state of the audio universe and other subjects while Brian solders a crossover together. When the xo is done he walks over and I start stuffing the box with xo and drivers.

When we get to the piezo, we squirt considerable hot melt around the coupling surface (face near the outer circumference) of the piezo, I say bad words while hot melt dissolves considerable skin on my fingers, hands, and forearm, and while the glue is hot I simply push the piezo onto the edge of the PVC inside the cabinet.

To check or replace the piezo, simply get like-diameter piece of PVC. You could use a piece of soft wood, but this will more likely crease the speaker cloth so I don't recommend that.

Cut a round piece of cardboard (or similar) same diameter as the PVC to save the piezo speaker cloth. Place the cardboard between the piezo spkr cloth and the like diameter loose PVC piece. Lightly hammer the top end of the loose PVC with a rubber mallet. Eventually the PVC/piezo piece falls into the cabinet cavity. You might want to prevent the piezo from stressing the piezo leads. Remember, it's a simple press fit, but some are tighter than others depending on hole diameter, wood swell, plus PVC is not exactly a precision piece of plastic.

Unsolder the leads from the piezo, connect amp to treble posts only, turn up planar/piezo L-pad to max, turn dome L-pads to zero, connect a known working tweeter to the piezo leads, and you should hear music from the test tweeter and the planar too.

Listen carefully with the tweeter stuck in your ear because this xo is very high, not much energy, around 10kHz. If it works, but the piezo does not, you have the first known blown piezo except for one customer whose entire xo flamed in most dramatic fashion (a VMPS museum piece if such museum existed). We had a few rare open piezo but this was known from the start, not like they worked then stopped working.

The planar and piezo share exact same xo and the planar and piezo are wired in parallel. Even if the piezo is blown the planar can still work (unless it's blown too).

If the piezo is blown, melt the glue with a heat gun and pry away the piezo and watch out the glue melts skin like nothing. Take an image of the piezo and place wanted ads. There might be a production number, I sure can't remember. Somebody's got a couple of those stupid things in their basement or closet. To test them requires an 8 ohm parallel resistor. They won't work without it. In the ST/R case the resistor is the planar tweeter in series (error earlier where I typed parallel, the planar and piezo are in series).

Actually, now that I realize the series connection, if the piezo does not work, the planar can not work, regardless the cause. One fails, both fail.

ST86 · « **Reply #43 on:** 23 Sep 2013, 12:44 am »

Checked my build instructions. The parts list only says "one piezo supertweeter" (the list is per speaker). No manufacturer or part number listed.

Shear Bliss · « **Reply #44 on:** 23 Sep 2013, 07:02 pm »

ALL SPEAKERS ON MY ST/R ARE UP AND RUNNING!!! The problem was centered on my jumper cables, I had made these jumpers a while back for my RM-1s out of extra Tara Labs speaker cables. The negative spade was sheared off making no top to bottom contact, a real easy fix.

Thanks everyone for all your help, suggestions on the piezo and JVC tweeter. I was getting ready to check the L-pad when I discovered the problem. James was correct, both tweeters were down but sprang to life, switch down, single wired.

Thanks again,
DW

James Romeyn · « **Reply #45 on:** 23 Sep 2013, 07:51 pm »

Cool!

I doubt anyone saw my edits, at least I hope not. Several times I went back and forth, each time convinced the planar and piezo were wired either series or parallel. Finally settled on the latter. Series would require an 8 Ohm parallel resistor on the piezo, unnecessary in parallel wiring.

A similar vintage model, the Tower II, came standard with two piezo supertweeters, one firing forward the other firing up same as ST/R (the only two VMPS with up-firing drivers).

Piezo has virtually infinite series resistance, which I suppose is why B said you could plug them into the wall outlet (don't try this). The infinite series resistance caused standard TII with dual piezo to need a parallel 8 Ohm resistor, otherwise no sound. Some TII owners (about half or more) upgraded to planar front firing supertweeter (replaced piezo in this position...we had to cut out the baffle). On such models the planar driver's series resistance replaced the 8 Ohm resistor. This supertweeter circuit (planar + piezo) is identical in both TII/R and ST/R, the only change between slightly different series capacitor values (same .2mH parallel choke in every planar-supertweeter equipped speaker B ever built of which I'm aware).

All supertweeter poles are 2nd order electrical.

PMAT · « **Reply #46 on:** 18 Mar 2014, 04:52 am »

Ok mr. Bliss. How about some current listening impressions of the rebuilt Tower/R.

Shear Bliss · « **Reply #47 on:** 12 May 2014, 03:33 pm »

This is a follow up on my ST/R speakers bought last year. These are in excellent condition only needing new foam surrounds on the 15" and 12" woofers. Millersounds Bill LeGall did the work, thanks Bill. I had started a follow up after the 15" woofers settled in then the 12" bass couplers went, so back to Bill they went.

I did modify the passive bass slot opening, adding 1 1/2" of height to it. Plus installing casters for easy movement, no more laying these down to make a putty adjustment is just ideal to me. I did vitrify the passives with yellow glue on the outer side only. I have the passives loaded per James recollection of Brian using 1 oz of fishing weight glued as a starting point tweak. Mine was hollow line thru type so was easy to flatten into a quarters size. I find using 6 to 6 1/2" of putty works best in my room.

Comparing these ST/R to my RM-1s not really fair, maybe the RM-2 a better fight! The RM-1 places better in my room but cant match the bass output or the midrange warmth I prefer in the ST/R ..... again apples and oranges. I do like the JVC clone up top over the spiral tweeter on the RMs, more reach and presence there. These portray a much more laid back manner through the midrange that just sucks you into the recording, in that sense James may be correct in that the Neo panels need help around 1Khz.

I chucked my Crown K1 for a Digital Amplifier Co. Cherry Ultra and there is no comparison, it is a sweetheart on the ST/R while not breaking a sweat. Works very well with my Classe 50 preamp thou I long to go back to a tube pre.

All this for a outlay of $200.00 ...... minus repairs! It just does"nt get any better than this.

Doug

James Romeyn · « **Reply #48 on:** 12 May 2014, 03:52 pm »

Exactly what I would have predicted. No replacement for displacement. I'd not mind owning that pair of speaker at all! The casters look cool on that model.

I gotta leave for an appt. Remind me and later I'll post brief story of that model speaker causing neighbor's pictures to fall off his wall.

ST86 · « **Reply #49 on:** 12 May 2014, 08:39 pm »

Hi Doug,

I am very interested in your opinion of the effects of the extra 1 1/2" of slot opening on the bass. I have foregone the putty pinching because of the need to lay the ST/R down every time I want to change the amount of putty. Using the default amount on the passives I bought from Brian a few years ago.

Just occured to me if the extra 1 1/2" has an adverse effect I suppose one could use the extra space to reach the putty, then add sheets of MDF or plywood to the slot to reduce it to the original height.

Anyway, even with the default amount the bass is quite impressive. Would be nice to conveniently dial it in though.

Thanks,

Ed

Edit: Here's another question. How do the castors affect speaker-to-floor coupling/decoupling?

James Romeyn · « **Reply #50 on:** 12 May 2014, 10:41 pm »

As I posted prior, over the years Brian employed some of my suggestions. Some more quickly (Scan Speak D2900) than others.

I made two matched custom woofer enclosures each comprising Brian's active poly (pale blue) 15" loaded by paper 15" PR (same as ST/R) with Brian's 4197 carbon loaded poly active 10" in its own sealed sub-enclosure.

The two active drivers fired forward, 10" above the 15". The PR mounted vertical on one side panel near the base, no slot, and IMO performed better than Brian's invention (slot-loaded down-firing) employed continuously from his first floor-standing Tower. Over the years I prodded Brian try this PR loading. No dice till his very last and best ever speaker, the RM50.

Brian eventually preferred my PR loading suggestion after he tried it. Apparently, efficiency of coupling to the room via open side firing outweighs the slot's capacity to filter alleged HF noise from the PR. PR mass is many multiples greater than air in a port. Gravity must minimize symmetry in the horizontal PR's in/out stroke (down/out minimum resistance, upward back into the cabinet maximum resistance) vs. any vertical loading (symmetrical stroke in/out), especially PR of such high mass. Further, I suspect the pedestal in close proximity to the PR causes PR output to reflect back into the cone, further minimizing its efficiency and disturbing its phase.

ST/R owners could cut their cabinet to move the PR to the side, but this obviously results in permanent cosmetic alteration. Returning the cabinet to OEM requires a big piece of matching veneer. For cosmetic PR cover on the RM50, Brian chose to make the RM50 cabinet panel thick enough (where the PR mounted) to inset the PR to allow approximately 3/4" thick cloth covered grill frame to press fit over the PR. When installed, the grill and side panel were flush.

If you cut, do NOT, I repeat, do NOT cut L/R holes to make a mirror image speaker pair, as Brian did in the RM50 (IOW, both L/R PR's fire either in or out). You want the PR in both L and R speakers to fire either L or R (direction does not matter as long as they both fire the same direction). The less is L/R bass symmetry the less excited are bass modes, the smoother is bass FR, and less are bass timing errors caused by modes. (Shameless plug: Above summarizes the philosophy of state of the art bass reproduction systems such as THIS, providing unheard of 6 dB FR window and virtually perfect time response in the bass range with no EQ, no acoustic treatment, and even in rooms with awful bass modes.)

To maximize non-symmetry, mount one PR as close to the floor as possible, mount the other PR as close to the top panel as possible (vertical non-symmetry). Vertical non-symmetry provides less non-symmetry vs. horizontal non-symmetry, hence the latter is more beneficial. Make sure the PR mounted high clears everything inside the cabinet (drivers, braces, etc.)

PS: Suppose all other items identical except one ST/R OEM slot height, the other has +1.5" slot height. I predict no one could reliably identify audible difference. I further bet $100 if one could reliably hear difference they'd prefer the latter, which would emit more PR energy and have less PR energy reflected back into the PR from the pedestal.

Shear Bliss · « **Reply #51 on:** 13 May 2014, 04:55 pm »

Hi ST86

When I decided to open the passive slot I was somewhat concerned it might screw things up a little, but not being able to make putty adjustments on the fly over ruled any other concerns. These sound just as good now as they did before I opened the slot height. I can now change bass tone via putty in mere seconds without moving my ST/R.

Read below for James take on opening the passive slot if you still have any concerns .....

At 150 lbs each I had no problem with going with casters. I can roll these BBs ...... (Big Bastards) out of the room and have my RM-1s running in minuets if I wanted to now!

Always refer to James, he knows the early VMPS speakers better than anyone out there!

Doug

John Casler · « **Reply #52 on:** 13 May 2014, 06:54 pm »

The size of the slot, and the size of the opening, provide a resistance to the Passive radiator, that Brian felt worked well.

If the volume and size of the opening are increased that resistance drops.

To compensate, simply "add" putty which will provide additional mechanical resistance to the PR, then fine tune from there.

ST86 · « **Reply #53 on:** 13 May 2014, 07:02 pm »

Doug, John,

Thanks. This is good news. I will put "make extended height tray for Supertower/R" on my list of projects. Tuning the pasives will be much easier with the extra room.

Any verdict on castors effects on speaker-to-floor coupling? I remember Brian was against using spikes. My floor is carpet over cement (Basement Home Theater Man Cave). I don't have the castors (great idea by the way), the cabinets do rock front-to-back rather easily.

Cheers,

Ed

James Romeyn · « **Reply #54 on:** 13 May 2014, 07:20 pm »

I'd like a ST/R owner to lay one speaker on its side, firing forward, PR away from adjacent wall. Listen to only that one speaker, program with deep bass, first with pedestal attached, then remove the pedestal and re-listen. Curious what might be the deep bass difference if any.

I don't think Brian realized it at the time (if he did he never said so), but I'm virtually positive most or all the perceived difference in tuning the PR is simply its effect relative to bass modes. Even differences between amplifier output impedance specs interact with modal effects.

Early Wilson WATT included two ports lengths for different amplifier output impedance specs (SS/tube).

John Casler · « **Reply #55 on:** 13 May 2014, 07:24 pm »

Ed,

Brian's idea on beards and no spikes was based on the propagation of the 360 degree pressures of bass waves.

They travel in a 360 spherical radiation, contained only by solid boundaries.

as the bass wave leaves the slot, it then radiates in that pattern. it will travel down the solid surface of the slot to the solid boundary of the floor.

The break in the boundary between the bottom of the slot and the floor allows some of that pressure to go into that opening, and "in theory" would slightly reduce the pressure that would come to you.

I say "in theory" because I tend to think that you wouldn't notice too much difference, or that the advantages of mobility might outweigh them.

James Romeyn · « **Reply #56 on:** 13 May 2014, 07:30 pm »

Quote from: John Casler on 13 May 2014, 07:24 pm

Ed,

Brian's idea on beards and no spikes was based on the propagation of the 360 degree pressures of bass waves.

They travel in a 360 spherical radiation, contained only by solid boundaries.

as the bass wave leaves the slot, it then radiates in that pattern. it will travel down the solid surface of the slot to the solid boundary of the floor.

The break in the boundary between the bottom of the slot and the floor allows some of that pressure to go into that opening, and "in theory" would slightly reduce the pressure that would come to you.

I say "in theory" because I tend to think that you wouldn't notice too much difference, or that the advantages of mobility might outweigh them.

I think that opening is audible. I'd plug the opening with any acoustically opaque material, even a piece of thick cardboard should work. Just cut it to fit the opening and lay it against the vertical front of the pedestal, resting on the floor. You are just making a very short beard.

Again, though, I'm not sure. Brian changed to the vertical open PR after I prodded him to do it, and I think it works better than the slot, but I'm not sure why. Brian agreed with me after he built the RM50.

ST86 · « **Reply #57 on:** 13 May 2014, 07:44 pm »

Interesting stuff. Thanks!

Ed

Shear Bliss · « **Reply #58 on:** 13 May 2014, 08:06 pm »

James/John,

Not laying my ST/R down no more ...... well worth the pedestal adjustment. I'm surprised the slot opening has"nt been more of a issue with owners over the years. The RM - 1 and 2s allow this extra room to make easy putty adjustments, I'm finally at peace. To me adding the casters was just a no-brainer for sure! Adding a little extra putty than the norm is a small price to pay to make the bottom end sound like it did prior to this mod.

I should have mentioned John also when referring to James knowledge of things VMPS, my bad, sorry John.

The putty loading still works its charm ... I pulled all putty off leaving the 1 oz lead in place and listened. As expected the bass thinned out with leaner bass impact, adding 8" of putty gave a thicker woolier muddier presentation. (In MY ROOM) 20 x 13 ..... 6-6 1/2" works very nice.

DW

James Romeyn · « **Reply #59 on:** 13 May 2014, 08:45 pm »

The room's dimensions are one parameter in a long list of almost infinite relationships affecting perceived bass quality. Other parameters are location of two speakers, listener location, boundary surface rigidity, etc. Change one item and the entire formula (and perceived bass quality) changes.

Note how perceived bass quality changes as you walk slowly around the room. As bad as are peaks and dips (15 dB windows are common), much worse is the negative effect on bass timing, as wrong bass notes ("synthesized" by the room, a product of bass waves interacting with room dimensions) continue playing even after a new bass note appears. This is, to me, the unforgivable error of bass mode effects on the listening experience.

A speaker engineer who deciphers and reviews loudspeaker patents for a trade publication agreed with me that bass mode effects comprise THD over 100%, just to provide a context of the scale and show how egregious are the errors involved.

After listening for the past several years with almost no bass mode effects, I'd quit the hobby if I had to go back.