Need a good high-pass Xover for Sonus REL

I would be one Audiogon member to disagree... introducing a crossover into the signal path might actually affect the resolution and the magic of the SF Concertos. Are you unhappy with the current sound?
If you have bass problems, I would first recommend investing in a sound level meter and a test cd with specified bass frequencies to see/measure if you have excessive bass or bass suck-out at certain bandwiths, and play with placement of- and the crossover setting of the REL. You can pick up a Radioshack SL meter for about $50 and a Rives Test CD 2 for $24 that is designed to be used with the Radioshack meter.
If you really have problems that require a crossover, I would look at the new equalizer from Velodyne, but that would be a considerably more investment.

And I join Arni and second the "disasgree" vote. I just went thru this discussion in great detail on another thread and offline. Let the Monitors' bass roll off naturally. Measure it if you can -- at what frequency does the bass START to fall off in volume, and at what frequency is its volume down by HALF. Set the sub's upper limit (where it STARTS to roll off) 10 to 20 Hz BELOW the half point frequency of the main speaker rolloff.

Here's an example:

Let's say the monitors' bass SPL (sound pressure level expressed in dB) starts to fall at 80Hz (at whatever you measure the SPL) and it's half as loud (ie down in SPL by 3dB) at 60 Hz. Then for starters, you'd want to start the sub roll off at approximately 40Hz (an equal amount the other side of the 60 Hz midpoint frequency) -- this is assuming the sub is putting out the same SPL at 40Hz as the monitors are putting out at 80dB.

The object is to have the two curves cross at 60Hz at half their SPL so that when added together the two curves form an (ideally of course) flat line.

IMO, and in that of the people at REL apparently, there's no reason to "clip off" the low end performance of the monitors. Doing that shouldn't make them "work better" if they've been designed well to begin with.
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Thanks for the info! I think I just neeed to tweek the REL's crossover a little.

Greetings
If you want to take the system up to the next level
The Vandersteen 5A High Pass units are the most transparent and simple solution you will find.
This is a big advantage with no downsides.
By high passing your system your amps distortion lowers dramatically cleaning up the whole system while not doubling up the bass frequencies. Once you experience
this level you will wonder why Rel didn't design it into
their subs in the first place.
Cheers JohnnyR

Greetings
If you want to take the system up to the next level
The Vandersteen 5A High Pass units are the most transparent and simple solution you will find.
This is a big advantage with no downsides.
By high passing your system your amps distortion lowers dramatically cleaning up the whole system while not doubling up the bass frequencies. Once you experience
this level you will wonder why Rel didn't design it into
their subs in the first place.
Cheers JohnnyR

Bob, you just don’t get it. I have read most of your posts. And I disagree as do many others here on Audiogon to your electronic crossover solution. I don’t think you ever answered the question "Have you ever heard a REL subwoofer?" and configured using the Neutrik high level cables? I have, and prefer it over an electronic crossover any day.

Woofers in a well made speaker have a natural rolloff and do not reproduce frequencies it can’t. That is where a REL subwoofer picks up the lower octaves. It works very well and sounds better than adding another component to your system. And to Stang500hpaol, that is why REL does not design a highpass crossover into their subwoofers.

Greetings Joeyboy
It is obvious that you have never heard a properly designed
Battery bias High Pass even with the big boy amps it makes it easier on them. Also lowers the distortion,cleans up the mids,= better transparency cleaner better extended bass
Dynamic range improved coherence.
Let me know when you would like to hear one.
Cheers Johnnyr

"It is well known that active crossovers have advantages over passive ones."

Maybe someone (Bob?) can share what these advantages are? Why are active crossovers superior to well designed passive ones?