I’m using a pair of 15" Rythmiks to supplement bass on my Avantgarde Duos, which have integrated woofers that do not go down extremely deep- when they are dialed up for more bass impact, they sound discontinuous with the mid-horn; when adjusted to blend with the midhorn, they sound anemic. The Rhythmic subs address that pretty effectively.
My task was made easier by focusing on the blend between the integrated woofers and the subs-- partly adjusted by positioning of the woofers (I had help in the form of two college football player types who did the heavy lifting). I also used a cheap little DSP unit- the Dspeaker 8033-- which is surprisingly effective to even out the bass in a decent sized room.
Once I ran the cycles on the DSP unit and it lopped off some peaks, I then zero’d in more-- lowered crossover frequency, adjusted slope and played with phase to get them to cohere. I had help here-- my wife- who adjusted gain, crossover and phase with direction from me sitting in normal listening position.
The system is very resolving at low volume and when the subs energize the room, you know it! But, you almost would not know they were there unless I shut them off. (FWIW, they run from a separate line out on my line stage, so the DSP is not in the same circuit as the main speakers). Even if you do measurements, final tuning is probably going to be by ear, no? Once set, I’m done. I do not mess with the settings for different kinds of music. The DSP unit sums the channels so it's mono. I know there's an argument there, but it is way easier to do and my main source is LP, which is often summed below a certain frequency anyway.
