Will a subwoofer add depth and clarity to my system, or just bass?


hi folks,
I just purchased a set of Focal Aria 906 speakers with stand, powered by a Bluestream PowerNode (not my ideal system but I had a limited budget).  I think it sounds really good, but am wondering if an upgrade to a subwoofer is worth it, and if so, what would pair well with this system -- my audio guy recommended the JL Audio D110 10" Dominion Subwoofer, but that's out of my price range.  Perhaps a SVSPB1000, for $499?  My room isn't very big, and I don't use the system for movies, just listening to mostly jazz and rock (and classical).
Thank you!
jazz99
@audiokinesis

Adjusting the continuous phase control provides much more than a slight amount of timing adjustment and my ears were quite capable of hearing when I had the correct phase setting. With such a range of adjustment it is possible to ruin the sound or optimize it with proper listening and technique.
Same for my car subwoofer- with time delay I was able to fine tune the proper delay relative to my main speakers and once you find the spot- car or home- the bass becomes effortless, deep, powerful and fully coherent through the range. The subwoofer then complements and works with your main speakers rather than fighting against them.  But again, the key technique was using beat pulses rather than pink noise.  
Thanks again, all, for an interesting weekend of reading and learning. I suppose one has to make a decision at some point, so will try to decide (after auditioning) between the SVS SB1000 and the JL Audio Dominion D110, which is unfortunately twice the price (but perhaps twice as nice).  I'm grateful for all of you for taking the time to weigh in on my question.
happy listening (and trails),
paul
You can lead a horse to water....

If you build it, the horse will drink lols.

I’ve had many customers claim to hear an improvement in clarity from the addition of subs without highpass filtering the mains, and I’ve heard it too, but cannot explain it, apart from the occasional situation described in the preceding paragraph. Of course there is also the improvement in clarity that can come from highpass-filtering the main speakers to reduce cone excursion, in which case the transparency of the highpass filter can be a factor.

I don't think I know why for certain but I can talk about some of my experiences.

When I replaced the cap in my tweeter xover with an expensive cap, one of the biggest improvement was the bass.  Also, if I disconnect the tweeter, the bass became a bit indistinct and mushy.  Why would the treble have anything to do with the bass?  

When the drum is struck, the initial impact from the drum stick creates a lot of high frequencies extending up all the way to the treble frequencies.  Then followed by the decaying sounds which are lower and lower frequencies as the decaying dying down.  So the drum is not just bass, ti has a lot of frequency contents - from bass to treble.  In the actually event, although the drum sound has a lot of frequency contents, all of them all arrive from one source therefore the sound is time and phase coherent naturally.

But when the sound of the drum is reproduced in a 2way or 3way speakers, the high frequcies and low frequencies of the drum all come from separate sources (tweeter, midrange, bass drivers) and our human hearing has to somehow reconstruct all those frequencies to give us an impression of a drum sound.  If your speaker is not well tuned, then the drum may not sound clean or well defined because my guess is the treble and bass frequencies are not as time and phase coherent.  If you have too much treble, then the soundstage my not be enveloping and so on.  If you have a lot of bass and not enough treble, the soundstage will be vague and not quite transparent.  Everything is is somewhere in between.

For example when I listened to Margin Logan, I always got an impression that the bass, midrange, and treble somehow are disjointed and not quite integrated, because subwoofer and the panels have so different speed that the sound stage is sort of odd.  So in this case, having a subwoofer does not automatically mean "better".  

And likewise so, if you already have a perfectly setup system, adding a subwoofer may actually be more harm than good.  So you have to be careful.   And of course, if your system may be a touch lean, not enough bass, then adding a subwoofer will compensate for the "leaness" and add some clarity to the soundstage.

Also it may have to do with a subwoofer filter design.  The subwoofer may use a shallow slope filter, hence its frequency response may extend all the way to the upper mid range or treble which in turn will have a lot  more affect on the overall soundstage - good or bad.  But if the subwoofer has a steeper filter design, the frequencies will be mostly in the bass, therefore the affect may be just bass impact and not as much in term of overall soundstageor clarity.