How do you high pass your main speakers?

I tried a Bryston active high-pass between my Ayre preamp

Same result with a different pre, just sounded off.

@dbphd 

I am glad to hear that Charlie Hansen (RIP - another bicyclist lost too early due to a vehicle incident) approved of the passive balanced Marchand high-pass filter that I recommended earlier in this thread.  That filter seems to do no harm in my system.

The effectiveness of using a high-pass filter, and the best-suited cut-off frequency and slope, will be largely dependent on the main speakers.  Main speakers that do well handling high current and rolling off at their lowest frequencies without issue are possible candidates to be run full-range with a sub rolled in at an appropriate frequency.  Main speakers that do not do well at the lowest frequencies, and speakers where the bass driver(s) also handle midrange duties, are more likely to realize a sonic improvement by using a high-pass filter to limit the depth of the low frequencies that need to be handled by the mid-bass driver.

My Aerial LR5 speakers offer the advantages of being a 3-way design (where the low frequency drivers do not also handle the mid-range) and having bass drivers that extend low, down to around 40Hz.  They are also quite dynamic and designed to handle high power.  The designer, Michael Kelly, suggested running them full range and rolling the Aerial SW-12s in to fill in the lowest frequencies.  I have found that set-up to work well but when something else in my system (DAC, preamp, cables, etc.) results in a more bass-heavy presentation, then adding the Marchand high-pass filter (45Hz cut-off) between my preamp and amps does seem to help without causing a sonic penalty.   

High passing the main speakers is something I would never consider.

Your ATCs make excellent bass, why would you want to take that away from them?

You can integrate subwoofers seamlessly without doing so.  

I’m familiar with ATCs (mine pair is the ATC SCM12 Pro passive monitor). These are sealed/acoustic suspension designs with terrific bass that disappears rather abruptly below the resonance frequiency, which I believe is in the mid-40s.

As for the high pass, after trying all manner of workarounds, I ended up buying a used but perfect-functioning electronic crossover, the Marchand XM66, which has 24 dB/octave slopes (ideal for your application) and a variable crossover. I’m accustomed to setting mine anywhere from 70 Hz to 80 Hz. That means:

-- all frequencies below the crossover point go to my subwoofer (JLAudio e110);

-- and all frequencies above the crossover point go to the ATCs, or the other pair of speakers I use on my desktop, the vintage KEF 103.2s, also a sealed 2-way design

I chose this crossover frequency because the sub is so capable in that range; while the ATCs, wonderful though their bass is, are working harder the lower the frequencies go to the resonant frequencies. So I relieve them of their hardest workload.

This electronic crossover is very transparent acoustically. I really can’t distinguish between it being in-line vs not being in-line.

That’s my recommendation: an external crossover with high crossover slopes. Note that Marchand also makes electronic crossover with fixed crossovers (via internal cards you can purchase). And example of that is the XM9. The most elaborate of their crossovers, the more expensive XM44, allows you to individually select crossover cards at the frequency and slope you specify.

@tony1954 wrote:

Actually my MiniDSP crossover is set to 80Hz for the subs so there would be a redundancy of frequencies from that 80Hz threshold and where the ATC's roll off around 54Hz. 

Perhaps it might be best to just tweak the crossover point a little bit lower to mitigate any spike between 54Hz and 80Hz.

Some prefer a slight overlap between the subs and mains, but I would use the supplied lower knee specs by ATC for your SCM19's and work from there setting an appropriate low-pass point juggling through the range here. The ATC's being a sealed design with a shallow lower end roll-off I suspect you would be better off lowering the LP from 80Hz and experiment with slope steepness. Using a DBA arrangement and setting delays, depending on the specific implementation, must be close to a nightmare to get right - although some may argue it's less important, but I digress. Your ears must decide, so whatever works, works (in my own actively configured speaker setup I use the same LP and HP frequency between the subs and mains with 36dB/octave Linkwitz-Riley slopes, so very little "redundancy" at the crossover. Proper delay settings here is of vital importance). 

Doesn't your MiniDSP have extra output channels? You already have all you need then to experiment high-passing your mains.