[Russtafarian]

I’ve been experimenting with bi-amping my RM30s for the past three years.  In short, it’s worth doing.  It unleashes the speaker in ways that are truly startling. I removed all the internal crossover parts except the tweeter crossover and potentiometer.  The midpanels (without the TRT cap/coil HPF and potentiometer) and tweeters are driven directly by tube amps with only a 300 hz line level 1st order HPF on the amp input.  This produces truly amazing transparency that has to be heard to be believed.  Plus removing the bass coil and electronically crossing over the woofers really uncorks the dynamic capability of the speaker. 

I started out with the Behringer DCX2496 that Brian uses for the Digital version of the RM30.  While it is incredibly flexible, I could never get it to sound right to my ears.  The DCX gave me the filet mignon in, hamburger out sound that I hear with virtually every DSP I’ve used (within my realm of affordability).  I did hear the Cullen modified DCX on the RM30s at THE Show Newport and that sounded pretty good.  But I think the modded DCX goes for close to $2k, which is above my price point.

Another potential XO contender is the MiniDSP.  It’ very reasonably priced (around $150 for 2way XO and $350 for 4way XO) and I really like the USB PC interface that allows me to adjust XO slope, frequency, phase plus parametric filters in real time on a PC.  I experimented with this unit for a few months and it has lots of potential, but again, filet mignon in, hamburger out.  I also briefly tried the DBX Driverack PA and that sounded absolutely disastrous. 

The XO solution I kept coming back to was an old Carvin analog electronic crossover that was retired from my church’s PA system years ago.  When I used it to crossover the subs and the RM30 woofers, I got very clean, time coherent (no digital latency issues) and tunable results.  By tweaking crossover frequency, level, and phase between the subs and RM30 woofers, I could effectively minimize the 70hz “room-boom” that is common in rooms with 8 foot ceilings.  But the Carvin had its own issues, most notably a 60hz hum that I could never get rid of despite all the different grounding schemes I tried. 

When shopping for low cost professional electronic crossovers, the Behringer CX2310 stood out in that it is a two way stereo crossover with an independent mono sub crossover.  It has a linear power supply with a toroidal transformer (one less switching supply to dump crap onto my AC line), a simple op-amp based circuit, and balanced XLR I/O.  Not bad for $80 delivered.  The PS and coupling caps can (and will) be easily upgraded to Panasonic FM/FC.  The 7815/7915 regulators can certainly be improved.  And if I’m feeling brave I’ll break out the ChipQuik and swap the 4580 SMD op-amps for 4562s.   

Hooking up the Behringer unit was straight forward since I already had XLR connectors on the all crossover cables (to connect to the Carvin).  I went through my usual setup routine using Room EQ Wizard to set general XO frequencies and levels, then fine tune with music.  Now that it’s about 90% dialed in, I’m getting all the performance benefits of the Carver XO without the noise and hum.  In fact, the Behringer has more range on the low/high XO frequency control so I can better tune and blend the transition from the RM30 woofers to the midpanels.

There is one thing this model doesn’t do that I wish it did.  The separate mono subwoofer XO works great for the sub, but it doesn’t correspondingly roll off the bass for the RM30 woofers.  This means the RM30s are getting all the bass even with the subs in play.  I guess I can’t have it all for $80.  Bummer.  I can work around this if I need to.  But If I really want this feature, I’ll have to splurge and get the $143 CX3400. 

[Pez]

Great mini review here! I'm glad to hear that you got active to finally sound good in your setup. The DCX can be tricky, not to mention that most (not all) people say it sounds pretty bad without mods. Tyson has an unmodded one that sounds pretty damn good to my ears, but he also has spent damn near 1000 hours to get it to sound as good as it does. I myself use a highly modded DCX to triamp my rm40s and it's damn near orgasmic. All that said, it's hard to argue with the price tag or the results of your cx2310!

[BobRex]

When you state that the RM30s are getting all of the bass, do you really mean that the RM30 woofers are getting the complete bass signal?  The Behringer manual is ambiguous about this, but page 8 says this about the subwoofer freq. control: "This control governs the crossover frequency between the low signal and the subwoofer signal (10-235Hz)."  This would tell me that that there are both low pass and high pass elements.  Otherwise all the control could do is blend in the subwoofer to the main speakers (ala B's PBS system).  So assuming Behringer's manual is correct (which in itself may be a long shot), how are you getting low bass on the RM30 woofers?

[Russtafarian]

BobRex, I'm going to investigate that a little further.  While I'm reasonably certain that my measurements and listening indicated no high pass filter between the sub and low output, I'll check again and let you know.

On a related note, this weekend I built a cable to solve my sub + LFE dilemma.  I needed a cable that would sum the balanced sub output from the Behringer XO with the unbalanced LFE output from my multi-channel preamp, then split the signal for the two balanced inputs on my Behringer sub EQ.  The cable used three single pair lines (from snake cable), a female XLR (XO sub out), a female RCA (LFE pre out), and two male XLRs (sub EQ in). I used 3.3k resistors to sum the XO sub and LFE outputs together in balanced mode.  The hard part was packing the three cables and four resistors into the female XLR. It was a PITA to build, but it works.

[Russtafarian]

Confirmed: the sub crossover control doesn't high pass filter the low output (which is connected to the RM30 woofers).  I wish it did, but it doesn't.

[Jon L]

Active bi- or tri-amping really changes the game, but as you're finding out, the active crossover really makes or breaks the whole deal. 

Like you, I always seem to hear a digital "character" or "artifact" from digital crossovers, especially the ones that does both AD and DA conversion.  But even software digital crossovers that does everything in digital realm still has a certain recognizable character to my ears unfortunately. 

After trying a bunch, I have found "acceptable" active crossover in the Bryston all-discrete active crossover, but even then, I have to bypass its volume controls and use my EVS ultimate nude attenuators in order to achieve acceptable transparency for my tastes. 

[Russtafarian]

Hey Jon,

Good to hear from you.  My solution to the active XO transparency issue is to go all passive to the RM30 planars and ribbons and keep the active XO operating below 280hz.  I though this would work with digital XOs but the latency delay really screwed up the coherence of the speakers.  I do use a digital EQ on the subs, but at frequencies below 50hz, a few ms of latency delay is not an issue.

Russ

[trebejo]

Why not Marchand?

[Russtafarian]

Why not Marchand?

That would be a great choice, but more than I can afford at the moment.  Lots of options to DIY or customize.  I like that.

[trebejo]

That would be a great choice, but more than I can afford at the moment.  Lots of options to DIY or customize.  I like that.

Indeed. Great then! I'll be keeping an eye on this thread.