VMPS RM40 Question

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OldiesButGoodies

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VMPS RM40 Question
« on: 13 Apr 2017, 09:33 pm »
Hi everyone,  new here,  hoping you can help me get up the learning curve on the RM40s. 

Mine are serial numbers 12652 and 12653 in what I think is brazilian rosewood:

IMG_0778 by Jose Sifontes, on Flickr

My initial question is simple - there are three pairs of binding posts - what is the purpose of the top set?   The previous owner used the lower two pairs, strapped with jumpers, to drive the speakers using a pair of monoblocks.  I would like to try biamping,  driving the tweets using a pair of VTL Compact 80 tubed mono blocks,  and for the bass I would like to bypass the internal passive crossover and use a minidsp 2x4 HD electronic crossover driving a pair of Channel Island Audio D-200s.  Does the uppermost pair of binding posts provide direct access to the woofers?  If not,  what is it for?

IMG_0779 by Jose Sifontes, on Flickr


John Casler

Re: VMPS RM40 Question
« Reply #1 on: 14 Apr 2017, 02:31 am »
Hi Jose, and Welcome to a very select group of speaker owners and aficionados.

I beleive your finish is Macassar Ebony.  Unless the camera is changing the color, the Rosewood is more RED.

You have me stumped with that 3rd set of binding posts, unless you speaker originally came with an OXO (outboard XO) which has 3 sets going into the cabinet.

Yours may be an early model, as Brian usually marked the TREBLE - MIDRANGE - and BASS.

Not sure what you should do.  I would check with the original owner, there may be a XO Box hanging around.

You need be EXTREMELY CAREFUL, since the tweeter can blow in two seconds, if you direct wire and amp to it.

Get a flashlight and inspect the ribbon on your tweeter to see if it is not shredded already.

If you really have an RM-40 made to have an OXO, then it would likely sound pretty bad, without the XO BOX.

But the more I look at it, the more I think the XO is inside, because you have L-Pad Shafts, and if it had an OXO, those would be in the OXO.

Another possibility, is that at one time we sold some "ambiance :dunno: :dunno: :dunno: tweeters" and they had to be wired from the main binding posts.  Maybe when making this pair, Brian just added a connecting pair. 


Stimpy

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Re: VMPS RM40 Question
« Reply #2 on: 14 Apr 2017, 11:55 am »
If those were my RM40's, I think I'd have to pull the bottom woofer and get a good look inside.  I'd do that before biamping, or even powering the speakers on again.  Just to verify exactly what is happening internally?  I wouldn't want to blow any drivers.  Plus, I'd want to see if all the speaker binding posts are even wired in circuit?  Maybe three pairs of posts were added when manufactured, to give the original owner the option to remove the internal crossovers, and add an OXO, at a later date, without having to mod both the cabinets and the crossovers?  Binding posts already in place, as a convenience?

Another thing, the rear label has "TRT" written on it.  I assume that this points to the fact that the speakers were upgraded with "TRT" capacitors?  As such, I'd think the speakers would have internal passive crossovers.  Why even note "TRT", if these were OXO 40's?

Good luck.

OldiesButGoodies

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Re: VMPS RM40 Question
« Reply #3 on: 14 Apr 2017, 02:18 pm »
Thank you for the quick response.  I will go ahead and inspect the actual wiring by removing the PR and report back.  They do sound pretty good as-is,  so I don't think anything is blown.  The previous owner included a spare set of tweeters in the sale. 

Macassar ebony sounds a lot closer to the finish - you are definitely right on that.

Thanks!

Jose

OldiesButGoodies

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Re: VMPS RM40 Question
« Reply #4 on: 14 Apr 2017, 03:23 pm »
Ok - looks like the top set of binding posts bypasses the inductors and goes straight to the two woofers,  which look to be wired in parallel:

IMG_0784 by Jose Sifontes, on Flickr
(far right are the upper posts,  the passive XO comes into play if power is fed to the lower posts)

IMG_0790 by Jose Sifontes, on Flickr


The PR appears to have been vitrified using poor technique by a previous owner:

IMG_0781 by Jose Sifontes, on Flickr

IMG_0782 by Jose Sifontes, on Flickr

Very cool design IMO - thank you Brian Chenney whereever you are in the hereafter! 

Now I can move on to testing biamping later tonight.  I have an assortment of tube and SS amp combos to try so it should be fun (I also want to test if the active XO helps control bass outcomes better, ideally guided by Room Eq Wizard and the UMIK mike to determine where the issues are if any).   

Thanks!

Stimpy

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Re: VMPS RM40 Question
« Reply #5 on: 15 Apr 2017, 02:21 am »
Fantastic investigative work!  Awesome.  Nice to find out that your RM40s are set up for biamping with the internal crossovers, or with an active external crossover as well.  Plus, the way the speakers are wired, you can biamp with an external crossover, and the tweeters will still be protected by their internal capacitors.  That's a good thing, as you don't want to spend $125.00 a piece for new tweeters, to replace tweeters blown by turn on transient thumps.

OldiesButGoodies

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Re: VMPS RM40 Question
« Reply #6 on: 19 Apr 2017, 12:47 am »
To close the loop on this - I am really happy with the sound using active biamping on the bass and passive on highs.  I used the miniDSP 2x4 HD as the active XO.  I can post more details if anyone needs it,  but suffice it to say that after a few cycles of Room Eq Wizard I was able to home-in on the right set of filters.  The crossover to the panels is set at 260 Hz 24 db slope.  Next I plan to replace the passive radiators with APR10s sourced from Solen, already ordered. 

OBG

Stimpy

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Re: VMPS RM40 Question
« Reply #7 on: 19 Apr 2017, 01:22 am »
Glad to hear that the miniDSP worked out so well.  Plus, active between the bass and mids seem to work the best.  Nice about the CSS APR10 passive radiators too.  I didn't even know they could still be found.  They used to be available on eBay, then disappeared.  It's good to hear that Solen carries them now.  Once they're installed, let us know your impressions.

ZAKski288

Re: VMPS RM40 Question
« Reply #8 on: 19 Apr 2017, 02:40 am »
  Nice about the CSS APR10 passive radiators too.  I didn't even know they could still be found.  They used to be available on eBay, then disappeared.
Hello Stimpy,  CSS  went out of business.  Solen had a few 10"passives left, now they are gone. Zak

DFaulds

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Re: VMPS RM40 Question
« Reply #9 on: 19 Apr 2017, 11:59 am »
Hello Stimpy,  CSS  went out of business.  Solen had a few 10"passives left, now they are gone. Zak

The PE RSS265-PR is a nice alternative.

OldiesButGoodies

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Re: VMPS RM40 Question
« Reply #10 on: 26 Apr 2017, 03:29 am »
I tried the CSS APR-10s in the RM40s and found them to be a too stiff for duty in the Rm40s.  Even with no weight added the cone was stiff and dampened the woofers too much. This is just my opinion, and my ears are 55 years old.  I put the originals back in after testing for two days.  I think we need to find a PR with Vas Cms parameters that are closer in spec to the original, IMO.  Anyone know the specs of the original passive?

Jose

Stimpy

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Re: VMPS RM40 Question
« Reply #11 on: 26 Apr 2017, 11:23 pm »
A passive radiator is all about it's weight, and how well it duplicates the air mass of a port, when it's tuned to the desired resonance frequency.  Then with absolutely no offense intended, are you sure you added enough weight during your testing?  To me, it sounds like the passive still needs additional weight / tuning.

As to the weight of the original passive radiator, I'm not sure.  I doubt that anyone knows, other than the original manufacturer.  But, I do seem to remember that Brian added a 20 gram weight to the cones center.  Then the rope caulk was added for final tweaking.  I hope someone else can fact check this, as I'm not 100% sure.  Though, I hope this helps!

Stimpy

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Re: VMPS RM40 Question
« Reply #12 on: 26 Apr 2017, 11:40 pm »
The Putty Pinching thread might help too.  Some of the info will be applicable.

http://www.audiocircle.com/index.php?topic=30236.0

audiomagnate

Re: VMPS RM40 Question
« Reply #13 on: 22 May 2017, 12:34 pm »
Glad to hear that the miniDSP worked out so well.  Plus, active between the bass and mids seem to work the best.  Nice about the CSS APR10 passive radiators too.  I didn't even know they could still be found.  They used to be available on eBay, then disappeared.  It's good to hear that Solen carries them now.  Once they're installed, let us know your impressions.

FWIW, I used a similar setup on my speakers which use the same drivers as yours (FF1's modded with 6 Monsoons and 2 FST's per side). After months of measuring and listening I'm now using a DCX2496 and crossing over between the Monsoons and the FSTs at 1.9K, L/R 24 dB/Octave. That gives me the lowest coloration and minimal "weirdness" when I move my head around near the sweet spot, which I was getting at higher crossover frequencies. YMMV of course, just thought I'd throw it out.

OldiesButGoodies

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Re: VMPS RM40 Question
« Reply #14 on: 22 May 2017, 06:14 pm »
A passive radiator is all about it's weight, and how well it duplicates the air mass of a port, when it's tuned to the desired resonance frequency.  Then with absolutely no offense intended, are you sure you added enough weight during your testing?  To me, it sounds like the passive still needs additional weight / tuning.

As to the weight of the original passive radiator, I'm not sure.  I doubt that anyone knows, other than the original manufacturer.  But, I do seem to remember that Brian added a 20 gram weight to the cones center.  Then the rope caulk was added for final tweaking.  I hope someone else can fact check this, as I'm not 100% sure.  Though, I hope this helps!

Will try the APR-10s again next weekend and report back,  adding more weight this time. A separate move to an active preamp (McCormack RLD-1) also helped the bass significantly.  These speakers  did not seem to like the passive!

OldiesButGoodies

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Re: VMPS RM40 Question
« Reply #15 on: 4 Jun 2017, 02:52 am »
Hi all

I put the APR10s back on and did several sweeps with various weights.  There is an improvement in response at 15-20 washers  (these things are subjective,  but look at the graphs too).  This is a 20-200 with no washers added, no smoothing:

RM40s APR by Jose Sifontes, on Flickr

Seems like I get a bit more bass heft with >15 washers, and that is how it sounds to my ears too,  so will it there for a while.  There is some wacky stuff going on with room nulls from hell etc (and this measurement was the right speaker,  which is in the acoustically ugliest corner), so it looks worse than it sounds. 

All this said,  the original seems better integrated and balanced sounding. At least to me.