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A little confused on how to properly integrate my sub

Hi everyone! Im relatively young and inexperienced when it comes to the more complicated electronics side of audio. Right now for my computer desktop Im using a a pair of LS50s connected to a Musical Fidelity M3si integrated amplifier. I also have an REL T9i connected to the finding posts of the amp and use the High level input like REL dictates.

Ive decided that I really want to properly crossover my speakers and let the sub handle ONLY the low end. I decided to put my Musical Fidelity up for sale and have ordered an Outlaw RR2160 that has integrated bass management. I plan on using a standard unbalanced RCA cable from the Outlaw to the REL. The problem is REL makes this very difficult. Unlike another sub I have where there is a switch that lets you use a filter in the sub or amp, the REL provides no such option. They demand you use play your speakers full range. The knobs on the back of the sub are LO/HI Level (volume I think), Crossover (30hz to 120hz), and .1LFE level (im not plugging into that input anyway).

I assume what I need to do is set the crossover frequency on my Outlaw to 80hz (where I want it), and then plug the Outlaw into the REL through the low level input, then crank the crossover on the sub to 120hz. The sub should only be receiving the low frequencies anyway so by cranking the subs crossover up all the way I shouldn’t be attenuating any frequencies. Does this sound right to you guys? THANKS!
EDIT: After thinking about it, is there any reason not to use the LFE input and bypass the subs filtering? As I understand it, all LFE content is 120hz or below so the sub designers took that into account.
collingraff
rhljazz
1,255 posts
 
Tithe -3 dB point for the LS 50 is 79hz.  Just let them roll off naturally and use the REL as the manufacturer intended.  You’re headed in the wrong direction.
stevecham
3,340 posts
 
+1 with rhljazz, good rec.
mofojo
2,303 posts
 
Yeah letting them roll off naturally will sound great if you don’t want to play them very loud. If you play music with any bass to those little drivers at full range don’t expect too much volume. Been there done that. 
mzkmxcv
777 posts
 
Get an SPL meter (even if a free one on your phone), use C weighting. Load up an online tone generator, measure how loud the LS50 is from say 500Hz-5000Hz, and get an average SPL level for that region. Then, lower the frequency until is drops 6dB from that average you found. Then, set the crossover  on the Outlaw on the sub and speakers at that frequency (maybe play it say and have a slightly lower crossover for the speakers, like if you found it to be 50Hz, set the sub crossover to 50Hz and maybe the speaker to 40Hz).  
  
Now, I assumed you did the sub crawl. Next, is phase (or in your case, cause REL are jackasses, a polarity switch). Whatever crossover the subwoofer is set to, load up that same tone generator website and play the crossover frequency tone (50Hz from the previous scenario), then flip the polarity switch until it sounds louder (use an SPL meter or have someone help, one person sits down in the seat and the other flips the switch), The louder setting is the correct one, as that means they are in-phase (if out of phase, they would negatively interact, decreasing output; in-phase interacting at -6dB leads to 0dB sum, so flat).  

Mans yes, use the LFE jack.
martykl
3,578 posts
 
You have a philosophical choice here:

The "audiophile" way is to play the Kef full range and integrate the Rel as Rel suggests. This is hands-off and maintains the simplest signal path.

The "rationalist" view is to actively cross. This will dramatically reduce distortion. The LS50 (like all speakers using smallish mid bass cones to cover LF) will show dramatically increasing distortion as frequency drops and spl increases. That’s physics. Actively relieving the Kef driver of duty below 100 hz will clean up low end distortion very effectively.

The question is whether it matters. Some say that the ear is insensitive to THD at low frequencies. You have to decide.

BTW - If you do decide to actively cross the system, I’d seriously think about an amp with a digital x-over and room EQ (per the earlier suggestion). It appears that you use exclusively digital source material and IMO crossing in the digital domain is the way to go. IME room correction is the single biggest improvement I’ve ever made to a high end set-up, but you can always defeat it if you prefer that route. (You won’t)
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