The response for REL regarding subwoofers

I think there is a limit to how much of a spread changing the gain on the subwoofer amp can manage. 
 

The average dynamic speaker is sitting between 87-95 DB efficiency. The Klipschorn is 105! 

At half a watt the KH is putting out 102DBs! The amount of gain needed for an amplifier to hit that output is very very very small. It gets worse as you get into more normal listening levels.

Think of how little gain would be needed to play those Khorns @ 85DB. 
 

The Rels, being probably more average in efficiency, would need a significantly higher amount of gain to match the output. 
 

Much higher than the gain difference on the subwoofer can accommodate.

Great explanation!

You could probably accomplish what you wanted with a pair of No.25 subs from REL, depending on room size and how loud you like to playback your music. 

That makes sense if you’re using the speaker level input. There might be other options, though you’d need to be careful and run the numbers.

With the speakers being so efficient, depending on your listening levels, the speaker level voltage could be within the limits of the line level inputs of the sub. There might be a way to modify the sub’s high level inputs for less attenuation as well.

You could run a sub out from your preamp at line level, but attenuate the signal going into the power amp and to the speakers. This depends on your amp input impedance. A passive pre amp would give additional adjustment. I think some attenuators can have roll off if the output impedance of the pre is too low. 

I’m sure there are variations of these, but it would depend on your specific setup and equipment. 

Horn loaded subs at 95+% sensitivity. Maybe a pair of 12" per enclosure, two enclosures. They are huge but that's what I use to run with Western Electric, VOTT or any Klipsch. Back then we didn't have to many box subs. There ones like REL but passive, the passive radiator was on the bottom too. It wasn't in an enclosed slot. 60-70s not too many manufactures made subs. You had to make them. Jensen Imperials Subs are a ton of fun. With 60-100 watt.. Your bumpin' pretty good.

https://www.decware.com/ImperialSO.htm

I had one and my buddy had one. When we had a party there was one at either end of the packing shed and a pair of Jensen Imperials. 

2 20 watt MACs and 30 watt Mac Kit for my sub and speakers and 60 watt MC60 for his. Would fill the whole joint right up.. 1969-72

That's what you need OP a big fat one dead center of those KHorns :-)

Regards

In 2001, I was using a Velodyne FSR18 with my Khorns and had no issues, mind you the neighbors did....

I’m using a GSG Devastator with my Altec A5 setup. It’s a 21” driver in a semi horn style enclosure. It’s powered by a Behringer 3000 dsp amp and I’m actually using the sub amp at about 75% on the gain and 35% on my Preamp volume and they blend well.  It is a huge cabinet though

Sensitivity is irrelevant. Volume level is what you need to match with subs, period. Clearly REL is capable of high volume levels. Cornerhorns achieve high volume with less power, but you listen to volume not power. Think about it. 

The wife is always playing with the volume control on her system if they weren’t matched like a La Scala with normal subs, she wouldn’t shut up. Having to get up and turn the volume up or down on 3 plate amps when there is a main speaker volume change.

I went from 84-5% Dayton Ultimax to 90% sub drivers listed below and I run 1/4 the power and reach lower than with the most 12" drivers. 4 in a 12cf column with 1 15" passive radiator. hit 120db and 16hz. It’s one of the best sounding columns I’ve ever heard for the money. I’m using 8" MB drivers and GRs OB servo on mine now, that Servo wouldn’t work either I don’t think, I’d have to look.

I use Behringer for bass duty NU12000. I keep 3 here 27 lbs brute strength class D pro amps. Well over 2500 watts per channel @ 8, 3500 @ 4, 4500 @ 2 ohms.

These 10" might keep up better let’s say.. :-) It’s my secrete weapon. Works very well in a 1cf sealed box to a 3cf with 2 12" radiators @ 18hz. Serious driver. Of course they went up 60% in the last year..

Isn't it nice to get an honest answer from a manufacturer that doesn't skew in the direction of them making a sale?

For sure. Honesty from a manufacturer goes a long way.

Seems to me the answer is simply to use an amp for the Khorns that has an input level control to attenuate its gain to the desired level to match the gain characteristics of your sub. Then use a preamp with sufficient output voltage to drive the system as needed. Of course you also need s sub with a high max output to keep up with the Khorns.  

My first instinct is their response was directed towards the use of the line level output. I would think the LFE connection would provide the ability to increase bass volume although integration with the system may be more challenging. 

I’m interested in an REL to pair with my Dynaudio XD power speakers. Thanks for the heads up, as I’m not sure how that would work. 
 

I’ll likely send them an email to make sure now.

Best-