[Vmeleco]

Just wanted to introduce myself. Just picked up a pair of rm30c speakers in piano black. I did quite a bit of reading here before I purchased

The passives are dry rotted, so I plan on just going to a pseudo version II route. I plan on keeping the current carbon woofers and adding the css10 inch passive. I guess I could tune them to 40Hz since the originals had reported response to 39Hz.

Vince

[GeorgeAb]

Vince,

Congratulations! How do you like that midrange, eh? Probably not sounding quite right with the gaping hole of the rotting passives, but should have an idea of their potential.   

Not quite following the "pseudo" version 2 comment. Is the pseudo not adding the 10uF capacitor? The series 2 is when you plug the hole where the two rotten passives are (cover with wood and glue, seal edges with caulk), remove the 10" driver, wire the two 6.5" in parrallel (currently they are in series and parrallel with 10"), add the css 10" passive (5 washers (counter weight) is good starting point for tuning per memory), and add 10uF capacitor across the approximately 30uF capacitor that you have. Sounds like you are doing everything except for the 10uF cap. The 10uF cap is for the midrange section. Below is a quote of a post concerning why to add the 10uF cap. Not sure about the explanation, but the 10uF cap will shift the midrange fc up and the addition of the 10uF cap makes the total capacitance more inline with what is used in the RM-40 and RM-V60.

User G E put a post on the modification with pictures that I found quite helpful when I did the conversion. https://www.audiocircle.com/index.php?topic=137131.0

The spare 10" drivers would be quite valuable for an RM-40 owner looking for spares to support their speaker. 

Again congragulations and have fun with your newly acquired speakers.

The woofers and mid panel circuits are parallel and to some degree isolated from each other.  But lowering the woofer impedance 1/3rd (6 Ohm to 4 Ohm) increases current through the mid panel circuit which decreases effective value of the series capacitor bank, shifting the pole higher.  Adding 10mf increases capacitor value, shifting the pole lower.   

Lowering the woofer impedance has inverse effect on the woofer series coil, increasing it's electrical effectiveness, which would shift the pole lower if there was no other change.  But in this case we also remove one 10" side firing woofer, and leave two front firing 6.5" with (likely) more mid range output.  The woofers are integral component of the electrical crossover so we can not predict changes in the acoustic pole and slope, pre vs. post woofer modification.   

[Vmeleco]

Thanks for the info George. Mine are the c version so no 10inch woofer, so assume I don’t need to add the 10uf cap. I say pseudo because I’m not sure if I have 28 or 40 oz woofers. I’ll tune for whatever sounds best depending on what woofers are in there. The 10inch passives are on the way so I’ll take things apart over the weekend. 

They sound very good so far, I’ll listen more critically after I get them fixed up. 

[Bob Stark]

Hey Vince,

You have the 40 ou. bullet shaped woofers that were an upgrade.  They don't bottom out like the blunt nosed 28 ou. woofers.  I bought 4 of the 40 ou. woofers from Brian when I had the other originally.  Made a difference on loud deep bass transients.  I am a Marcus Miller, Stanley Clarke, Jaco Pastorius, etc. bass fan.  There were those that said they 40 ou. woofers didn't make much difference in SQ.  For bass fans, it did--so enjoy.

[Vmeleco]

Great!  I confirmed this today as I have these apart to prep for the css 10 passives. Do you have recommendation for tuning fs

 of the passive?

[Bob Stark]

Hey Vince,

How thick is the material the passive would screw into?  I did this mod about 10 years ago.  My pair had about 1/8" of cabinet to screw into so I added a 1/2" layer of MDF epoxied to the inside with the circle cut out just like I see in your picture.  I had to use 8 clamps and leave it to dry for a day to make sure before removing the clamps.  This gives you 5/8" of material to screw into.  You could also use 3/4" MDF to get even more to screw into.  That might even be what I used.  Cut the MDF in half before glueing so you can get it in the speaker box.  Use mortite--plumbers rope putty--as a sealer with a strip all the way around the underside of the passive before screwing it on.  The extra mortite will help give some mass to the middle of the passive.  The correct amount will be determined by ear with the music playing.  Don't put the cover on until you get the amount of mortite right.  These speakers can sound just about any way you'd like by how much mortite is used.  I think a 6" piece of mortite rolled around itself so it looks like a mini cinnamon roll w/o the frosting.  This is a starting point.  Take a small amount off at a time while listening.  Just to what you like in bass.  You can always remove more--should be about a pea size piece taken off when you're done.  Do your listening with the speakers in the positions you determined they sounded the best. 

There are some good links in the VMPS speaker section of Audio Circle.
Good luck and have some fun,
Bob
Have fun,

[Vmeleco]

Hey Bob. I didn’t add any material as I felt there was enough to grab. Maybe 1/2 inch or so…the walls are quite thick.i have the css 10 passivives which use a screw on weighting system. I used 7 washers each based on what I had read here. I haven’t taken any measurements as it sounds pretty good to my ear. I’m using a sub xcrossed over around 40Hz.

I do have a question if you or anyone knows:  has anyone installed 2 additional woofer where the original passives were? It seems to me that the passive I’m using has plenary of Xmas to accommodate such an arrangement.

Vince