How do you high pass your main speakers?

There’s optimally and very very good, @mijostyn . :) I wager I can get to very very good, but rather than dicker in hypothetical arguments I’m going to put my money where my mouth is. I find that more convincing. :)

Yes, absolutely being able to control high and low pass is the easiest way to integrate a satellite and sub, but in many cases a user is specifically choosing a non-DSP based preamp and processor and hence my solution.  BTW, my solution is not unlike what Vandersteen does in some cases.  The Vandersteen solution is sound and mine is based on similar principles.

I’ll post back when I have got my project working. :)

@erik_squires    As someone with hands on experience, and after getting plenty of positive feedback from A’goners who have actually tried it, I believe that most everyone who high passes their main speakers, via a line level crossover of some sort, finds it a wonderful end-result.

A very good point erik.

If most of those folks could hear the comparison between David Hall's Velodyne 2011 Digital Drive Plus high pass vs its basic twenty minute Auto EQ, I'm certain the Auto EQ would be the hands down preferred choice. Since the sale of the company it seems any further updating of the twelve year old software has stalled while prices have more than doubled making it a questionable recommendation. 

@mijostyn     1.The only way eric that you can do what I have been talking about is with digital signal processing. 2. Using digital signal processing to "room control" the subwoofers wastes a lot of power and stresses the drivers. It is better to use a cleverly designed room and subwoofer array to keep nodes to a minimum and use dsp sparingly.

mijostyn +1  I found this to be case with 7.1 home theater (same speaker hight and distance) setup from the listening position. This greatly reduced dependency on processing and a far more enjoyable surround. I was taught how to map the rooms low frequency standing waves in the late 60's by the guy who sold me his Octavium, my first subwoofer. 

I can't speak to the prospect of digitizing the entire audio band as a means to control subwoofer room optimization, that's another topic. Despite my main speakers and the two DSP subwoofer systems providing what seems to be the best of both worlds, I'm still interested in hearing your impressions with DEQX. 

I am in agreement with @erik_squires 

Read this article

http://www.troelsgravesen.dk/High-Pass-Filter.htm

Thanks @perkri !

I paricularly think that audiophiles should focus on this sentence from Troels, which is in alignment with my previous statements:

But not having the midrange driver pumping deep bass has a positive impact on the midrange as well and it also relieves the power amplifier of some back-EMF coming from the speaker drivers. Pretty much a win-win situation.

While Troels is discussing a 3-way system with a dedicated midrange this is essentially the same as taking a 2-way and adding a subwoofer. High passing the satellite has enormous audible benefits that outweigh all of the puritanical nit picking by far.

Re: the OP and his sealed ATC SCM19 main speaker design with its huge magnet, large 3" and underhung voice coil SL-woofer, the distortion numbers here are already quite low up through the midrange, and my previous "leave it as it is"-answer (i.e.: don’t mind high-passing them) was partially in relation to this context. Granted, as a sealed design there’ll be excursion maxima at the tune, and thus there will be some influence into the mids at more elevated SPL’s with low frequency material exciting the cones into prodigious movement, not least if/when the voice coil exceeds the gap and its linear motion, but at more typical listening levels it’s a lesser issue.

Question remains: when will the efforts of high-passing them be worth it, and naturally this depends on the specific implementation of a HP-filter among other things. Given a fully active DSP-configuration steeper HP-slopes can be easily chosen, and it’ll make the HP-function and its sonic implications all the more effective. A mere 1. order slope here will still have some "bleeding" into LF-territory and is really only a half-baked solution - even with an 80Hz HP. Myself I’m implementing a HP over my mains at ~85Hz, 36dB/octave L-R slopes, and that’s with dual 15" woofers per channel w/100dB sensitivity and 800W continuous power handling - that is, tested with material into the bass region, so add a bunch of dB’s of effective headroom when high-passed as described. What’s interesting with such a powerful main speaker system is the difference a HP still provides for here; natively a ported design tuned at a relatively high 40-ish Hz, high-passing them removes the character of the ports, cleans up the mids even further with sharper leading edges, and seamlessly "delivers" them to a pair of very efficient 1/8 space loaded tapped horns that are quite "characterless" as well - not least when compared to the sonic imprinting of a variety of dual 18"-loaded direct radiating subs. All of this makes for a more seamless integration with the horn section from ~600Hz on up (111db sensitive). Indeed, here a HP over the mains makes a world of difference.