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

Dear @noble100  : ""  It's much more difficult to attain good bass response in most rooms than it is to get good midrange and treble response, ...""

no doubt about.

There are some " problems " with passive speakers design even with full range models as could be the top Wilson, Magico or any other:

main trouble/problem is that a full range passive designs are handled by " universal " amplifiers. Amplifiers designed to performs not in a specific frequency range but to performs all over the frequency range and designed to make a whole good work. The amps are not designed to match in specific the woofers overall needs, so it makes a " so so " job and that's all.

In a self powered subs as my Velodyne's ( out of production. ) the designers of the subs took in count every woofer characteristic and how and what to do for the dedicated amp can fulfill it.
A true advantage in the Velodyne's is its very low distortion levels that Velodyne achieves  checking over 16K times for second the woofer excursions to not permit over 0.5% ( normally performs way down that figure. ).

So , it's not only important to have an evenly bass room response but with low overall distortions.

Bass range is the foundation of MUSIC in a home room/system, as better the bass as better the overall quality performance levels of that room/system.

Look this room/system:

https://systems.audiogon.com/systems/615  

the " center " of the system are the Evolution speakers that are a true full range design that uses a pair of self powered subwoofers sealed towers:


http://www.evolutionacoustics.com/loudspeakers/mm-series/mmseven/

R. 

rauliruegas,

     I think those Evolution Acoustics mm-series twin self-powered sub towers certainly look impressive and like they'll reproduce very good bass.  
     I believe it's possible to get very good in-room bass response in most rooms at a specific dedicated but relatively small section of a given room usually referred to as a 'sweet spot' with only 2 subs regardless of size or price.  I believe that low distortion bass is beneficial if the bass is still perceived as low distortion/accurate bass once the bass sound waves are launched into the room, some of these bass sound waves arrive unaltered directly at the listening position and other bass sound waves arrive at this listening position altered after reflecting/bouncing off of 1 or more room boundaries and the brain processes these multiple bass sound waves, arriving within milliseconds of each other, by summing them.  

     Once the 2 subs are properly positioned properly in the room to provide good bass response at the dedicated 'sweet spot', however, the bass response will not be consistently perceived as good throughout the entire room.  The bass will be perceived as exaggerated, attenuated and even non existent at various specific spots in the room where room bass sound waves meet. 
     I also suggest you may have been too trusting of information produced by Velodyne's marketing department concerning the audible difference between bass sound waves produced by one of their self-amplified subs versus those produced by a competitor's passive sub powered by a good quality external amp.
     Getting very good in-room bass response is definitely not as simple as buying the 'right' brand and model subs and plopping them down at convenient positions in the room.  Principles of physics, psycho acoustics, the material composition of room boundaries (walls, floors and ceilings)  and even the physical dimensions of the room itself are all important factors in a dynamic environment.

Tim 

Dear @noble100  : Maybe I do not explain me very well ( normally in me. ). 

It's not that I'm deep founded in the Velodyne's subs. What I try to say is that evenly room bass range  must start with those  ( 2 0r more. ) self powered subs that by specs has the lower self distortion figures.

Again, today for home audio systems the only self powered subwoofers with lower than 1% distortion levels is the ones coming from Magico $$$. It performs that way with measured 136 db SPL.

Velodyne is out of audio market.

The main reason that moves me to buy and integrate two subs in my room/stereo system was to achieve the lowest overall distortions I can under my own room/system limitations.
My room/system main target is to stay nearer to the recording and first parameter to approach that target is to mantain any kind of distortions ( coming from every where. ) at minimum.

In my room/system I confirm that Harman International is rigth on what their white papers I linked conclude: ideally 4 but with two subs you can achieve almost same quality level and there explain about.

I don't disagree with you even that I know you are in deep about the use of 4 subs and in Agon forums there are other gentlemans where their systems approach is the same of yours and are truly satisfied.

According with what other audiophiles/musicians and me already experienced in my room/system seems to me that I really am lucky that with 2 subs have not discernable problems developed by bass range at a sweet pot not extremly limited and certainly not wider as over the enterely room, of course not. My system is at the parlor of my house and more than a true limitations for the bass response I think that already helped for that " lucky " scenario I pointed out. My subs are positioned at a very unorthodox place.

Btw, seems to me that you are an expert in this overall bass range subject and certainly I'm not but only a " lucky " guy.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

rauliruegas
You might want to think a little about that 1% distortion number. Not whether it is true or accurate, but whether it matters. When it comes to really low bass, its hard to see how it matters.

Low bass waves are 30, 40, 50 to even 60 feet long. So long that before the speaker even gets to the end of the first wave the beginning of the wave has already hit and been reflected off the walls many times. But not just reflected. In hitting the walls it moves them, and they move back. This energy in the room from the walls turns out to be one of the toughest to eliminate. About the only thing you can do is build a wall specifically designed to absorb and dissipate this energy, then suspend it over another more structural wall. This is what Geddes does in his room, what some professionally designed studios do. Its not cheap.

But if you don’t do this then you have the walls radiating that energy right back into the room. So no matter how low distortion your speakers, they wind up in that room having five, ten, twenty percent distortion.

That’s just one form of distortion. Standing wave modes and nodes are another, probably even bigger form of distortion.

This is all a part of the bigger picture, which is how speakers interact and work within the listening room. Too often specs are quoted that while accurate turn out to have little or nothing to do with real world performance.

Dear @millercarbon :  """   then you have the walls radiating that energy right back into the room. So no matter how low distortion your speakers, they wind up in that room having five, ten, twenty percent distortion. """

even higher than those figures. Is there a possibility that that " effect " can goes at minimum just at random? I know that " sounds " crazy but exist that possibility?

In the other side and in a " normal " home audio room dimension the very low bass range due to the limited room dimensions not even " form " its bass notes waves: I think ! ? ! ? ? as I said I'm not an expert but only a music lover and audiophile.

And if does not " forms " then what's what we are listening/our body sense? Some times at my seat position I can feel/sense th bass waves at my ankles, sometimes a little elevated body sensation but neither distract or makes an overall degradation of what I'm listening through my ears: clarity, transparency and the like always is there and I can't detect that that kind of low bass " sound " affects   the TT/tonearm/cartridge behavior.

Coments are welcomed on this regards. Is there a way to explain it?

R.