Converting the RM30M and RM30C to Series II RM 30

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Brian Cheney

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Converting the RM30M and RM30C to Series II RM 30
« on: 6 Oct 2011, 07:37 pm »
RM30 M:

Remove the side firing 10" active woofer and detach the wiring.  The two front active 6" and the active 10" are in series/parallel.  Lay the speaker on its back and unscrew the active 6", laying them face down on the front baffle. The new configuration is a straight parallel wiring of the two front 6"  Discard the jumper wire and connect the neg (black or unmarked) wire from the crossover to the top 6" neg. terminal lug, then make a connection from there to the neg. terminal lug on the bottom woofer.  Similarly, connect the pos (red purple, or lettered strand) woofer wire from the crossover to the pos. (red dot) lug on the top woofer, and connect a wire from there to the pos. lug on the bottom woofer.

Locate the 10uF cap supplied with the upgrade kit and wire it in parallel with the midrange caps (large bundle w/red wire attached), and solder in place.  You will have to remove the fiberglass damping material inside the cabinet to access the crossover, located on the bottom terminal board. Reinstall this material when finished.

After this is done, install the 10" PR and follow the instructions for the RM30C conversion.  You must return the old active 10" to the factory.

Brax

Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #1 on: 5 Apr 2013, 02:50 pm »
What exactly does adding the 10uF cap do to the cross over points?

mrcasey69

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Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #2 on: 5 Apr 2013, 08:56 pm »
Quote from Brian: "you add the 10uF cap to compensate for the lower impedance of the circuit when the active 10" is taken out."

Quote taken from this thread:

http://www.audiocircle.com/index.php?topic=94954.0

Reply #9

James Romeyn

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Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #3 on: 6 Apr 2013, 12:31 am »
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.   

Brax

Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #4 on: 10 Apr 2013, 02:58 am »
Since VMPS is no longer, where would anyone recommend I purchase 2 of the TRT DynamiCap 10 uF caps? It looks like they are going to run $45 each from the sites I have seen.

John Casler

Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #5 on: 11 Apr 2013, 06:03 am »
Those caps are currently available and should be for the foreseeable future.  Not sure you need to stock up.
 

$43.95 from Michael Percy  PercyAudio.com


mrcasey69

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Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #6 on: 5 May 2013, 09:26 pm »
I am in the process of upgrading my RM 30 M’s to Series II.  I noticed that one of the banks of caps in one of the speakers’ crossovers has only 3 caps attached (not four).  There are no remnants of a cap that broke free.  It appears as though the fourth cap in the one crossover was never there.  I am wondering if this is something of concern that I should address now or if Brian built these like this for a reason?  It terms of sound and measurement both speakers performed the same when they were running in my system.  Shall I just go ahead and install the 10 uf caps to both crossovers and ignore this or is there another cap I need to add to the crossover that seems to be missing one?  Attached photos are wide and close shots of both speaker crossovers.









« Last Edit: 6 May 2013, 12:16 am by mrcasey69 »

John Casler

Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #7 on: 5 May 2013, 10:24 pm »
It is not unusual for the XO parts not to match.

Brian would measure the systems separately and combine caps that reflected the needs of each system.

Not all drivers measure exactly the same as far as impedance and this would affect the XO values he used.

In fact I am of the opinion that a mirror image XO would be the exception and not the rule.

mrcasey69

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Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #8 on: 6 May 2013, 12:13 am »
Thanks for the response John.  I suspected this was the case but it is good to get confirmation from somebody who knows this stuff.  I will go ahead and solder in the 10 uf caps and move ahead with the upgrade.

PMAT

Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #9 on: 6 May 2013, 05:01 am »
It is not unusual for the XO parts not to match.

Brian would measure the systems separately and combine caps that reflected the needs of each system.

Not all drivers measure exactly the same as far as impedance and this would affect the XO values he used.

In fact I am of the opinion that a mirror image XO would be the exception and not the rule.

It is certainly time to do measurements here or it will always bother you. My RM-1 crossovers were dissimilar and were measured as being different x-over points and I had them repaired. Don't most speaker builders try to match drivers for quality control?

mrcasey69

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Re: Converting the RM30M and RM30C to Series II RM 30
« Reply #10 on: 6 May 2013, 05:41 am »
I have measured the speakers with frequency sweeps and a calibrated microphone.  The speakers matched up fine within the scope of room interference.  I measured the mids and tweeters separately from the bass drivers.  The mids and tweeters on both speakers start to drop off sharply at the same point approx (280 hz).  Post modification I will measure again and see what difference, if any, the 10 uf caps make.