Hi OP,

Unfortunately I don't see an easy way for you to accomplish this.  Your integrated has preamp outs, so you can connect your sub's line level (RCA) inputs this way but there's no way to limit the amount of bass that reaches your speakers.  However, you can plug the ports, which I often recommend for 2-way speakers with subs.  This will somewhat reduce the excursion below the tuning frequency but reduce the output so you can turn the sub up higher.  this will make it easier to integrate the two.

If possible however an approach that did let you put a high pass filter in line with your main amplifier would improve upon that.   Maybe talk to MW and see if they have a suggestion? 

yes, my system has a DSP tool as the DAC/Pre/Streamer that also has subwoofer outs and a bass management system so integrating a subwoofer is less tasking with it. So, unless you're willing to change your system I guess others can chime in @cooper52 

That's pretty much what I figured after failing to find anything online. I'll just deal with things as they are and integrate the new sub (yet to be decided upon) accordingly. My previous sub, a REL S/2, worked seamlessly once I got the settings to my satisfaction. Don't really have any interest in doing a wholesale system change just for this. And anyway, I really like the Modwright and would be hard-pressed to find anything within my budget that I think I'd like half so well. 

@cooper52 

Your speakers have decent bass down to about 44Hz -3db.  You can add a subwoofer and set the low pass filter for 44Hz and no need to high pass the main speakers.  

You paid for decent bass from your speakers, why not use it? 

Many subs have active high pass crossovers.  Lots of people use this configuration.

My setup has a separate preamp/amps....I split the preamp output signal and sent part of the signal to an active low pass crossover set at 63hz that then feeds the line level inputs of an integrated amp.  The speaker outputs of the integrated amp feed the 8" woofer of my main speakers, plus it feeds the high level inputs of my active subwoofer, and I set the low pass of the sub at 50hz with reverse phase. 

The other side of the preamp output feeds my monoblock tube amps....there is a 10nF silver mica capacitor that acts as a high pass inline filter that restricts low bass < 63hz to the tube amps, and passes everything else to the 5-1/4 midbass and tweeter that use a passive crossover.

I ran the above configuration without the inline high pass crossover (10nF cap) to the tube amps for a while, and I thought it made a notable improvement once installing it, but every situation is different so it may or may not be a good solution for  you.  I know it sounds complicated from a glance, but it’s not bad, and this setup evolved over time... it made sense in my case and has worked out extremely well for me.

You can start out inexpensive with Harrison Labs in line filters. If it works for you can decide on more expensive solutions like Marchand or JL Audio. I high pass me mains at 50 Hz before the amp. It really helps the sub integration.

There are a couple of options for you. The JL Audio Crossover is an excellent choice.  Another option is the SPL Crossover which I use. Both units allow you to adjust the low and high crossover points on the fly. This does require a separate power amp for the subs, but most subs today have their own built in power amps. The benefit is reducing the demand on the primary speakers allowing them to focus on rest of the music.

+1 @avanti1960 !

I agree with running your speakers full range.  I have the option of setting both the low and high pass filters in my main system.  I find I like the sound better running the speakers full range and now full range out to my subs using the preouts.  I even switched off the low pass filter on my subs.  You need to have a room that is well setup acoustically and I dial in the volume on the bass but it works for me.  I’m a bass guy which is a good thing because only my dog can hear the high end anymore.  Suggest experimenting with your settings and find what you like best.  It’s a fun part of this hobby for this old guy.  

While some choose to use a high pass filter to the main speakers with sub(s), I think there are many reasons to not.  A lot of popularity with high pass filters comes from AVR surround sound, where there are Dolby settings in the AVR processor for this.  the theory is that it cleans up signal going to small main and certainly small surround speakers.

But for great stereo imaging, and disappearing subs, getting the most bass cues possible to your left and right speakers helps immensely. Your ear can localize tones quite low, so using the low pass filter on the sub prevents you from localizing these sounds. Think plucking of the bass string vs the deepest tone it creates.

As @avanti1960 said, you have respectable bass output with your speakers, use it.  This allows the lowest possible cut off for your sub. 
 

Additionally, adding  any filter, processor etc in line with your speakers potentially inserts distortion.  I work very hard to avoid this.  No room correction, Roon processing, graphic equalizer etc. 

I am not knocking quality high pass filters.  But at best they add complexity.  I have enough wires!

the only reason I would consider not sending full signal to my mains is if the woofers were flopping or distorting.  And most quality speakers with good amplification do not do this.

KISS

I'm one to try and keep things simple.  There have been lots of thoughtful comments and I agree that it's usually best to play the speakers full range and then have the sub reach up to that point and fill in.  

Outboard DSP or anything else added to the signal chain will raise the noise floor and is always a tradeoff.  

Start in the shallow end of the pool.  Get your sub and do you best to integrate it.  Unless your room is particularly problematic you should have some great sound.  Only if the sound is unsatisfactory move to the deep end of the pool and add something else in the signal chain.  Good luck and cheers. 

@avanti1960   +1

Adding complexity and restricting the speakers won't help anything. They are design to be full range.

@cooper52 I actually did it myself. I built two high pass filters, one for each channel as I’m running my Audio Research Ref 5SE to two separate ARC Ref 250SE mono blocks. The monoblocks feed a pair of Revel Performa F328Be speakers.

I got some help designing the second order high pass filters from GR Research (they were happy to help me without charging me a dime, which was very appreciated) and I will be happy to share the circuit diagram with you. What made it a little bit more complicated for me was that I’m using balanced connections between the line stage and the monoblocks, but it’s only a few more components.

This does indeed relieve the main speakers from, in my case, anything below 80 Hz, and of course my two subwoofers have low pass filters and with REW I can make sure everything melds really well.

Comments here saying that "main speakers should always be run full range," in my humble opinion, don’t know what they’re talking about. I believe there’s absolutely no basis for that statement, as then in its extension you would say that you don’t believe in crossover filters, as high passing the upper part of the frequency range to the main speakers and let the subwoofers take care of the lowest frequency duty is exactly the same thing as what a crossover filter does inside the main speakers.

@gdaddy1 per my comment above, in my opinion your comment is simply not true

@bimmerlover   Your speakers have triple 8" drivers for excellent bass resonse.

 24Hz (-10dB); 26Hz (-6dB); 35Hz (-3dB)

By crossing at 80hz. you cut them off at the knees. Why buy a speaker this capable and then put a choke on them? I'd bet the triple 8" drivers produce BETTER, tighter mid-bass in the 35 to 80hz range than your subwoofer.

It's called a "subwoofer" for a reason. To lift the line in the sub region. For you the sub would come in around 40hz. It's NOT a woofer. You have triple 8's for woofers but instead your asking the subwoofer to handle this mid-bass range and hobbling the very capable triple 8" drivers. Why buy them if you don't use them?

@gdaddy1 if you know anything about logarithmic scales, at -10 dB it has dropped to a meaningless sound level, so has essentially -6 dB.

The F328Be:s taper out at 35 Hz at -3 dB, which is still a meaningful sound pressure. One of my subs, the KEF KC92, goes down to 11 Hz at -3 dB, a huge difference, and I low-pass filter it at 100 Hz.

In addition, the tube power amps are not that great in controlling the lowest bass as they have a relatively low damping factor. I trust the sub's 2x 500-watt solid-state amps to do a better job controlling the bass drivers.

Besides, I picked 80 Hz, but anyone can choose their preferred high-pass frequency. It is, after all (still, but unfortunately in peril) a free country.

@cooper52 I have an suggested experiment that you could try. Your integrated has both pre-outs and HT-bypass. So, you could send the signal from the integrated’s pre-outs to an active crossover, then at the crossover, fork the signal, sending the higher frequencies back to the integrated’s power amp (via HT-bypass) and the lower frequencies to your subwoofer. 

Options for your crossover include Sublime Acoustic’s K231, maybe a MiniDSP, or a JL sub crossover. 

My experience. I’ve heard a JL crossover + subs in a buddy’s system. I think it sounded great. I haven’t heard the Sublime unit--I’ve only seen OCD Mikey recommend it on his channel as a solid contender for the money. 

I’ve done what your describing with my TV system. In my TV system, I currently use KEF LS50 Wireless II’s, which have their own internal DSP engine with both high and low pass filters. I paired them with a REL HT sub. I had initially tried the crossover at the speaker’s -3db point (45hz) and at 70-80hz (often recommended in HT situations). I left the crossover at 80hz to live with for a while. Then, one day, I found someone’s charts showing when the LS50 speakers distorted across the frequency spectrum and at different volumes. I don’t recall the exact chart figures, but each chart showed distortion across the frequency spectrum when playing the speaker at different volumes like 80db, 85, 90, 95, 100, 105. What I saw in these charts was that starting at some volume, say 90db, that all frequencies 100hz and below were above some distortion percentage while frequencies above 100hz were not distorting. Charts at higher volumes saw a greater distortion asymmetry across the frequency spectrum. From that information I hypothesized that I should try handing off all frequencies below 100hz to the sub to see if I noticed any change in the sound. I went into the KEF software and changed the crossover to 100hz, and even though I wasn’t listening at 90db, the system sounded more effortless. (I also tried setting the Xover to 120hz, and that sounded equally effortless to me.)

Still today, I have this hypothesis that (1) some systems can benefit when offloading frequencies to subs typically handled by the speakers, that (2) crossing the subs over higher than usual (higher than 80hz) can be effective, and that (3) that a good setting for the crossover is the point where your specific speakers begin to distort asymmetrically across the frequency spectrum. 

If you get into JL’s sub integration philosophy, you’ll learn that they’re big proponents of offloading low frequencies from the mains, and of crossing over at higher frequencies, even for expensive speakers that are "made to play full range." But, I haven’t seen JL articulate where to set a crossover at. Anyway, audio is an experiment, and in experimenting with this philosophy, you may find a solution that works for you. 

Marchand Electronics makes a variety of high pass filters and crossovers designed to limit the low frequencies going to the mains. While my mains are very capable down to 40hz, my room acoustics favor the low frequencies near the floor rather than 30 inches above, where overall things sound best. It's not a matter of philosophy, it's listening and creating the right system for your room and tastes. 

As for using a sub for below 40hz, you'll find very little musical information there. Few instruments produce frequencies that low. Its great to have it available but its not something you're going to hear often.

But by using a sub for below 80 or so, you have a speaker specifically designed for those low frequencies rather than a woofer that is expected to produce those as well as much higher frequencies. 

@bimmerlover 

if you know anything about logarithmic scales, at -10 dB it has dropped to a meaningless sound level, so has essentially -6 dB.

The F328Be:s taper out at 35 Hz at -3 dB, which is still a meaningful sound pressure. 

Exactly my point. You want the subwoofer to pick up that lower range. Those speakers do 35hz and up really good but you're not going to let them do their job. So, why did you buy them? Because they look impressive but you're only going to use half the drivers capability? Makes no sense to buy something and not use it because the tube amp is mis-matched to the capability of the speakers.

FYI... bass in music lives in the 35 to 80hz range where your speakers are optimum but your amp is weak.  

It's your system and you are free to set it any way you want. However, it's not good advice for everyone and could hinder more than help.

@gdaddy1 if you don’t like my approach, which I have explained in quite the length, why don’t you quietly move along. I was merely responding to the OP as I believe I have some relevant experience relative to his question. 

First of all deep bass is totally non directional. I've seen audiophiles stand right next to a sub crossed at 65 Hz and tell the demonstrator the sub wasn't working. The demonstrator had to take the grill off the sub and have the listener put his hand on the sub and it was roaring away. All 'sub' directionality comes from harmonics.

Secondly adding a high pass takes a huge load off the woofers of the main speakers and if done properly the frequencies above the high pass become more open and defined and dynamic. I know. I had stand mount SEAS Froy 3 speakers to which I added big woofers crossed with 4th order Linkwitz/Reily high and low pass filters at 85 Hz and it only took seconds to hear the improvement in the sound. The but is a simple generic high pass may not work. It may take a specialized high pass to work with your mains. The advantage of rolling in a sub where the mains roll off is the high pass is no longer a problem. But you're only getting half the advantages of adding subs.

@avanti1960  another +1 for the same rational as @gdaddy1 +1.

I was unable to enter the ELAC RS500 Manual. I found their Auto Room Correction claims uh, interesting.  

Forget me. I think you'll finally get to hear and feel the deep end of audio. Free shipping, product support and easy return policy. Bravo Elac!

Certainly seems like no brainer.  

All the best

M

JL audio's CR-1 active crossover will do the trick. About $3500 new I think, tons of flexibility for crossover points for high and lows, dead silent and transparent, excellent reviews. Feed your pre amp out into it and then your "trimmed" high level output back to your amp input; run the "bass" output to your dedicated subwoofer.

bimmerlover  thx for great posts and great advice
i was going to suggest asking GR engineering in texas too! YES he is fan of filters high pass etc they work he can sort you out ( if one would help! ) 

Funny how so many here forget he wants help w/ HIS system  SO droning on about YOUR system may not be helpful?  keep it in mind ? i KNOW you want to brag ! sometimes we should STFU 

you beat me to it ! Danny there what a gentleman generous and helpful w his time ,send an email or call  fair and not greedy in buisiness! will test ANY speaker for FREE ( call first  make sure he has not already tested it ! ) yea you pay for shipping both ways ( get a free  acct w/ pirate ship buy pre paid labels email to anyone shipping you something save up to 60% off reg UPS shipping and bit on USPS too + if YOU buy the label , email it to seller , save $$ on shipping ( A LOT! )+ YOU get the insurance $ IF it gets damaged ! lost never thought about that did you ? LOL !   if THEY buy label THEY get $ !  ok hopefully you will get a refund ? 

so yea it DOES help main s speakers sound better almost everytime if you cut off info on low HZ send to subs and yes we should all use subs 
i think you said $1500 limit so suppose the GR research dual 12" open baffle, servo sub kit is a no go but i would find the extra  $  and go for it ! 
GR Research dual open baffle kits, like the "Double Trouble" and "Flatpack,"GR Research dual open baffle kits, like the "Double Trouble" and "Flatpack," are known for delivering fast settling times, high resolution, and detailed bass performance. They offer flexible configuration options, including mono or stereo, and are often used as a foundation for full-range systems. Users praise their clean bass lines, spacious soundstage, and holographic imaging. 

Double Trouble and Flatpack (Single)( one ), two speaker kit 

Rated 5.00 out of 5 based on customer ratings

$1,710.00–$1,718.00

A minidsp SHD (not the best quality perhaps, but your mileage may vary) can be used as a streamer with bass management, if you intend to keep the modwright in the chain. They also have other models in their product list.

For a more polished/ turnkey 1 box solution, the Yamaha R-N2000A amp (w/ integrated bass management features) will do it really well. I got to measure this unit.

Accuphase used to make some very high quality units

etc

Guys like @phusis may have suggestions on other items that can be used to achieve the above.