Vertical bi-amping with RF-5s

[erik2A3]

A couple of days ago I mentioned our recent acquisition of a pair of RF-5s. We know the reference series was designed with two pairs of binding posts: one for HF, the other LF.  This of course makes it possible to bi-wire the speakers with your wire of choice for midrange and high, and, perhaps larger AWG for the woofers - both of which connected to either a stereo amp, or single channel monaural amplifier.  The owner's manual also encourages bi-wiring over a single run (with binding posts strapped).

 

Since I have the means to do this with a number of matching solid state and tube amplifiers, instead of bi-wiring or simple bi-amping with a mono amplifier, I decided to vertically bi-amp each channel with a pair of stereo transistor power amplifiers (Hafler DH-120s).  Note this is NOT bridging the amps (which can be done with them) for mono operation, but rather using them in stereo, with one channel driving the HF section of the RF-5s, and the other channel (of the same amp) connected to the Low.  For the signal input, a Y jack is connected to each channel of the preamp, and a dedicated interconnect for the L and R inputs on the amp is connected to the opposite end of the Y.  For those of you familiar with Vandersteen loudspeakers, this is an approach that is also strongly recommended beyond bi-wiring and/or mono bi-amping.

 

And the results here were immediately apparent to me over the use of either a single stereo amplifier or my mono block 300B or 2A3 amps.  My dear wife is taking a nap after very early morning meetings for work, so volume is much lower, but I'm impressed by what I'm hearing in terms of improved frequency response and separation of instruments (really overall stronger three dimensional soundstage) even at these low levels.

 

Amplifier pairings of hence greatly expanded, where it would be possible to use a lower power valve amp on the HF, and something stronger on the low end.  I have also ordered a pair of RF-7 compression drivers to replace, or at least audition, the OEM HF drivers, and can make some small adjustments to crossovers (primarily driver impedance at crossover point) as needed -- which may or may not be audible.  We'll see.  Moreover, I can control output levels of my amps, and thus adjust the HF and LF crossover branches (really two separate networks) individually.

 

I haven't had more fun with this in a long time....for lots of reasons...but it's so nice to be able to have this kind of flexibility with a pair of speakers that already sound very, very good!   

[jjptkd]

11 hours ago, erik2A3 said:

I have also ordered a pair of RF-7 compression drivers to replace, or at least audition, the OEM HF drivers, and can make some small adjustments to crossovers (primarily driver impedance at crossover point) as needed -- which may or may not be audible.  We'll see. 

 

I haven't had more fun with this in a long time....for lots of reasons...but it's so nice to be able to have this kind of flexibility with a pair of speakers that already sound very, very good!   

 

Glad to hear you're having fun, to me that's been a big part of this hobby over the last several years. I actually ran my RF-5's with RC-7 drivers (same as the RF-7's) and crossovers and really liked the improvement. 

 

 

[erik2A3]

I found your thread yesterday, jjptkd, and it's good to hear or see, depending on how one's looking at it, that others have gotten great results from the change -- despite what others say to dampen the enjoyment or personally perceived improvement.  That's just how it's been here sometimes, and I've been coming to this forum since about 2004 (at that time under my user name (which is my name) Erik Mandaville.  So, excellent!  Thanks for sharing. It's something that helps broaden the experience associated with this specific modification -- and in so doing helps others new to the RF-5s benefit.

 

What I am considering (as of about 10 minutes ago when I thought about it) is removing the networks from the cup altogether, and connecting only the drivers to their respective binding posts (on the inside of the cabinets). I would then rebuild the crossovers externally in order to find the best balance in terms of capacitor type/brand (I've used the very reasonably priced Daytons in the past in been just fine with their performance).  The woofer filter will remain as is, except for perhaps larger AWG for the .5mh choke on the woofer.  The Zobel network would also stay the same. 

 

Using an external crossover frees up space on the back of the input cup, and there is flat area just above the binding posts that would accommodate a variable (rather than fixed) L-pad to balance the HF section to my own personal taste.  We must keep in mind, of course, that ANY change -- such as suggesting to someone a different brand or type of capacitor -- is a deviation from Klipsch's already extremely competent engineering.  The point is that we all have personal priorities, tastes, etc., regarding how we want our reproduced music to sound; and all are legitimate if the end result is one that doesn't compromise the electrical safety and working tolerances of the equipment being used.

 

Years ago here, we would go to battle over the use of resistor-based L-pads (either fixed or variable) vs the autoformer (which Klipsch no longer uses) as a means of attenuating the bandpass driver in a 3-way Heritage system.  Instead of the work required to desolder and resolder autoformer positions, I found it far easier, more efficient, and ultimately more accurate in terms of achieving finer steps of attenuation, to use a variable L-pad.  It does not change the reflected impedance the way autoformer steps do, and so the value of the input-to-network capacitor does not have to be changed in order to maintain the same crossover frequency.  There were always arguments about how resistors waste amplifier output as heat, but I just never had a problem with that in terms of what I actually heard -- and I had been using extremely low power amplification with our La Scalas and K-horns.  Moreover, I actually found the a-former to sound sort of veiled or lossy.  If others can hear distinct differences between capacitor brands and dielectrics, I can hear the difference between a resistor and a multi-tapped choke (aka: autoformer)!  

 

I applaud and support your experimentation, and it helps me think that I may be on a similarly good track with our new/old RF-5s!  Looking forward to the arrival of the new compression drivers!

[Joecoulson]

Fun is the most important.  For sure.  
 

I would strongly recommend running REW with the new setup to make sure the top and bottom sections are equally resistant. I found this out after running exactly the same amps on HF and LF only to find that LF was about 5ohms and HF was about 3.5. Which of course threw off my balance of range. 
 

not saying that’s the case, but even if you have exactly the same amps, measure and see if your missing anything.  

[erik2A3]

Sure, good point.

 

Even when I started building my own speakers and crossovers in the early 90s, I found I tended to prefer the HF response a couple of dBs or so higher than LF.  That's one of the advantages, at least as far as my own experience, of having an variable L-Pad on the tweeter.  Other well-known companies like JBL and Altec, just to mention two from a multitude, approved of them for the same reason.  Otherwise, they wouldn't have put such a user-adjustable element into the equation.  

 

But you bet!  I have the means to measure output levels and will definitely take your advice on that!