Your sub experience: Easy or hard?

I have just this week been looking at some changes to my sub situation. My main speakers with two 9-inch drivers each in a very inert acoustic suspension cabinet perform very well with bass down to around 40Hz. I have been very happy with the sound resulting from rolling in two subs and cutting them off at around 40 Hz.

In discussions with the manufacturer of my speakers, he believes what I am doing is fine, but that I could gain improvements with a high pass filter set for 45 Hz, which could reduce doppler distortions resulting from the woofers reproducing lower midrange frequencies up to 360 Hz while at the same time trying to reproduce very low frequencies in the 30-45 Hz range. Marchand is in the process of building a passive balanced HP filter for me.

It is also my speaker/sub manufacturer's experience that two subs run in stereo (which is how I use mine) are superior to one mono, or running two in mono. He believes we can localize stereo sounds in the low bass to some extent making it worthwhile to run the subs in stereo. Regarding more than two subs, it is his experience that adding a third sub run in mono and located in the back of the room can provide significant improvements in bass, while going from three to four subs is much less of an improvement. He recommends adjusting phase using a trial and error method from the listening position. I have been planning to add a third sub but haven’t yet found one of the SW-12s that I use anywhere close to where I am located.

I forgot to mention we are talking about two different buzzes. I mean the vibration you feel as if you feel the string moving.

@mijostyn 

My main speakers use dual 15" drivers each. They can shake the house pretty well; everywhere except the listening chair 🙄  So I added a pair of subs, thus creating a DBA because the subs are asymmetrically placed. Now I get the same bass impact (and 'buzz'...) at the listening position that the rest of the house gets.

@atmasphere , you put your listening position in a null spot! You evened out the amplitude response in the room. It would be interesting to measure the group delays of the system before and after you added the additional subs. At what frequency do your 15" woofers cross to the midrange horn?

you put your listening position in a null spot!

Yes: 'Nulls' are caused by standing waves. It was exactly the only spot in the room the listening position could be located. Move three feet in any direction and no problem. I am very lucky in that my GF likes the stereo quite a lot (helps when it sounds good) so its in the living room rather than a mancave.

The 15" drivers cross over at 500Hz. They are field coil and quite fast, but so is the midrange driver.

My tapped horn subs, two of them, are big at 20 cf. per cab (and each weighing around or +200lbs incl. the driver, built in BB 13-ply), and handling such behemoths certainly isn't easy.

Once positioned is their respective corners (a placement chosen to flank the mains symmetrically and to take advantage from boundary gain) integration with the mains and overall acoustics from hereon has been a work in progress, mostly with regard to finding the proper delay setting as this has been done by ear (sorry, @mijostyn).

Tapped horns as well as the more classical front loaded horns can be tricky to hone in on wrt. delay (unless done with microphone + software), because there's not really a wave front outset to visually outline as a starting point, if you would, the way you can with a direct radiator. Some delay compensation with horn-based subs is a necessity, and knowing the horn path length helps, but with a tapped horn the front wave isn't initiated at the front nor back wave of the driver (positioned at the tap/mouth of the horn), but somewhere between the front side of the driver and the mouth.

Different delay settings have been been tried out via different presets, with a very good balance and mid bass energy now found. I have had my speaker setup (though with other, passively configured mains) measured out in both the time and amplitude domain and corrections done via software, but with my current actively configured setup I've only applied PEQ corrections (aided with measurements; completed by ear) on the top horn section via my Xilica DSP. A more complete software correction in both the amplitude and time domain may be implemented down the road.

To conclude: integrating my subs hasn't been downright easy so far, but having high-passed the mains beyond 80Hz, actively as well with subs sporting low group delay, decent phase behavior and no overhang, while having a professional, elaborate digital cross-over tool like the Xilica makes it a fairly straight forward process and a great way to harness the potential even further. Had I used digital correction tools to begin with the process would've been easier for sure. 

As is the results are great; of-a-whole coherent sound, and totally effortless.