Will these subwoofer be enough ?

No, not really.

Your money will go farther and much deeper here. Give them a call  

https://www.rythmikaudio.com/?gad_source=1&gad_campaignid=21382262560&gbraid=0AAAAADMvRGO9-ZynSjOsde9TkIbH155ZT&gclid=EAIaIQobChMIp8LP--yEjwMVIi3UAR3Xeys6EAAYASAAEgJ6nvD_BwE

The Klipschorns are very efficient, and you'll need some gain to keep up with them.  You'll get a lot more bang for your buck with Rythmik and they measure and perform very well.  Two subs are definitely better than one to help cancel out peaks and nulls.  Rythmik will modify the E15HP2 subs, which fit in your budget, so that they have enough gain to keep up with the K-Horns.  Are you looking for the best value and performance, or audio jewelry?  If it's the former, go with Rythmik.  If it's the latter, REL.

Having mono blocks has nothing to do with the number of subs needed.  It's more room and listening experience dependent.  2 subs are usually better than one, however they are considerably harder to integrate than just 1 sub. Once dialed in though, they can be fantastic.

Depending on how loud you like your music, the 2 REL Classics should be fine.  They do look nice and would look much better than many other offerings on the market with your KHorns.  I'd take the 2 Classics over a single 15" carbon.

 “601 mono blocks with new Klipshorns mk6"  wow talk about over kill. you may not be getting the bass you expect due to never getting that amp out of idle. 

Regardless, after years of trying to find a sub for LaScala’s I would recommend a servo sub or at a min a sealed design. This is to keep up with the horn loaded bass that’s much faster than most subwoofers out there. Integration will be the larges issue.

Also assuming you have the speakers in corners.

Actually never said not getting bass I expected. The bass is fine and a big improvement over the vintage horns I just replaced.  I love the horn speakers. yes they are in the corners Although the new horns do not have to be , they still produce most bass in corners.  I would just like some more.  
I listen only to two channel music with this system and quite loud in a fairly large room.  Just looking to add “ some “ fast additional bass  . appreciate  suggestions thus far 

thanks 

+1 @big_greg 

I run a pair of Rhythmic F12SE subs (with the high gain option) alongside 1980s vintage Klipsch Belles (Sensitivity: 104 dB @ 1watt/1meter) and get good results with lower listening levels of blues/jazz.  I run them all off a 20 wpc Quicksliver integrated tube amp.  Simple and not overly elegant - but sounds pretty decent.  As always, YMMV.

I run modded Khorns with  two REL T9X, this most coherent sub integration I've ever experienced. I don't need much from subs with the careful placement and complete seal of Khorns into corners, I've sealed at sides with water pipe insulation, custom top cap, again sealed to walls. REL's are perfect integration with various amps I'm running 845 SET, 300B monoblocks, Bendix 6094 push pull monoblocks. Running only one run of wire to positive binding posts, one negative to amp chassis grounds, sub crossover at 32 to 35hz, volume only a few notches above minimum. In room bass response at listening position is spot on.

Hello hardhattg,

Check out https://hsuresearch.com

I’ve been very pleased with my subs from Dr. Hsu (pronounced “shoe” for several years.  I use them on both my tube (mostly music) and SS (primarily home theater) rigs.  I’m fortunate that I live just a 30 minute drive from his facilities in Anaheim, Ca.  Dr. Hsu is a brilliant and down to earth guy that loves to talk subs. He answers the phone quite often or his assistant, Kevin will.  Great folks and serious bang for the buck subs.  As always, enjoy the music. 

While I have no direct experience with REL or Rythmic subs, I do with Hsu. I can confirm Hsu makes fine subwoofers that represent one of the best value and performance offerings on the market. I have a couple of his older column subs and they continue to serve me well. I can also recommend SVS as a source for good quality subs. SVS has a phone application that includes parametric eq so the subs in room response can be matched to the rest of the system. I can't say enough good things about this app and how much less effort it takes to get a reasonable blend between subs and mains. With a 4k budget you could get a pair of the their newest subs (15") in sealed box form, and for the size driver, the enclosures are relatively small. A pair of these in vented configuration would be noticeably larger and provide more output but would put you over budget. Nice thing is SVS gives you a free trial period to see if you like them or not... and if not, they are returnable for full refund. in the marketplace as it exists today, there isn't a much better deal to be found that I have run across. 

I like the overall sound of Khorns, though I have no recent experience with the version that is made today, back in the 80’s I knew a guy that had a pair of the then current model driven by a Harmon Kardon Citation 16 power amp and a Soundcraftsmen preamp that truly was a mindblowing system. He could crank that up and thru the closed doors and windows you could hear it a 1/2 mile away over top the traffic noise from a busy 4 lane highway. I have no clue what the actual decibel output was but it was up there. At anything like reasonable levels it sounded wonderful. My only real complaints boil down to a lack of very low bass extension, especially for their size.  They really would not work in my home, at least the way it is currently arranged, but it would be fun to live with a pair for a while just to see how it would be to do so. 

I'd look for a pair of used REL s812 - they're running around $1800-$1900 each and are better and will go deeper and are very well reviewed. And yes, I'd get two of whichever you end up with, a pair make more output, cancel nulls in the room and you can run each as a separate Left/Right. 

It really depends on what you are trying to do. If you are trying to accurately reproduce music. Then the subs you are looking at will do that. If you are looking to pressurize the room and overemphasize the lower bass, then larger subwoofers may be required. 

When I visit folks systems the first thing I typically notice is that the cross overs to the subs is too high and they are way too  loud, creating a huge bump in the bass... instead of an even transition and flat response. If you turn the subs up too loud, they will scramble the imaging. It's about what you are trying to do. I used to have two subs... they ran at less than 10% power and crossover of something like 40 hz. They extended the soundstage nicely. But it was so easy to turn them up too loud. 

@ghdprentice

I used to have two subs

Just interested in what you have now and why you changed?

I upgraded my speakers from Sonus Faber Olympica 3 to Sonus Faber Amati Traditional. I felt I no longer needed them. The perfect coherence top to bottom, make me very happy with the sound. 

I was a planar speaker person for a couple decades. Subwoofers always part of the solution. I had heard that dynamic floor standing speakers could have excellent coherence... the same character from top to bottom. I never knew what is was until I got these speakers... I instantly understood. Extending the bass and trying to feather in different sets of speakers to boost the 28hz to 20hz range did more damage than good. 

I don’t listen to hiphop and don’t try to rattle the house. I listen to rock, jazz, world, classical and electronic. 

In my experience 2 subs sounded much better than one in the 2 systems I’ve setup.  Started with just one both times.  Best to plan for 2 in my opinion. 

Thanks to everyone that responded thus far.  Some great information here.  
I am not looking for booming bass at all and about 70% of the music I play the horns have enough bass for me.   Just wanting to add a little more for certain music but must be seamless and not overbearing but make a noticeable difference if that makes any sense.  
 

thanks to everyone so far and please keep responding with your experiences / opinions. Very helpful 

@hardhattg Your second post only reinforces two REL subs exactly what you're looking for. I was looking for the exact same thing in adding subs to my Khorns. I've had conventional subs with low level connections, dsp, far more powerful bass than the REL's, they always brought attention to themselves through excessive boom or discontinuities with main speakers. With the smaller REL's running at present one wouldn't even know I'm running subs, the integration/coherence makes it sound like Khorns that simply reach lower freq than typical of Khorns. I'd actually rate the improved sound stage as a greater improvement than greater freq range. I wouldn't even call it added bass as I don't have any freq overlap between Khorns and subs. REL's preferred connection scheme via high level speaker binding post means subs flavored by amps to some extent, this adds to the coherency thing.

Anyone have any experience with these specific classic REL subs ? 

@sns   I've had conventional subs with low level connections, dsp, far more powerful bass than the REL's, they always brought attention to themselves through excessive boom or discontinuities with main speakers.

I don't mean to be confronting, would you mind sharing exactly the make and model of conventional subwoofers you're referring to?

Where did you position them within the room?

Anyone have any experience with these specific classic REL subs ? 
 

I have a Classic 98 that I purchased as a demo from TMR. No shame in being honest: I purchased blind and purely for aesthetic reasons to match my Tannoys. 
 

Just wanting to add a little more for certain music but must be seamless and not overbearing but make a noticeable difference

The 98 replaced a Rythmik F12G that had PEQ, variable delay/phase control, low pass slope, crossover, and an extension filter. On the other end of the spectrum is the 98 with just its 0/180 degree phase switch and crossover.

It took me a while to understand all of the settings in the F12 in addition to a lot of experimentation on placement for better integration. F12 is a better subwoofer, but the 98 effortlessly integrated with less localization. I just chalked it up to user error and lack of knowledge on my end in respect to the F12G.

I’m planning to purchase a second 98. In my system the 98 provides that seamless integration and difference in the lower end - the invisible anchor that subtly shows itself when needed in the soundstage (like most good subwoofers). Aesthetics matter to me, and the Classic line helps blend into similar looking speakers and systems.