Do you use a Subwoofer when listening to stereo?

I have sub set at Lfe 120 hz thru settings, no special connection.  Not sure how often lfe freq are used by sound engineers.  Is this a big deal?.

Does excluding sub from stereo make sense?


     No and here's exactly why in your case:
     Your B&W 804D3 speakers are very high quality, expensive and have a rated bass output extension down to the audible lower limit of 20 Hz.  However, it's highly unlikely that you're experiencing and enjoying bass response this deep at your listening position because the woofers, that are responsible for launching these very low frequency sound waves into your room are permanently affixed in their cabinet. This rarely discussed design flaw is true for any speaker, no matter its design type, that has a rated bass extension deeper than about 80 Hz. 
     This permanent affixation of bass transducers in a speaker means they're not capable of being independently positioned in your room, and in relation to your listening position (LP),  which is required to optimize the perceived bass response at your LP from 20 Hz up to about 80 Hz.  The truth is that, even if the bass transducers in a pair of speakers are launching pristeen deep bass sound waves into the room, it's highly unlikely these sound waves will reach the LP in the same pristeen condition.
      The explanations for this reality are detailed and best understood via physics and how humans perceive sound, especially below about 80 Hz.  The deeper a sound's frequency, the longer its corresponding full cycle sound wave and the higher a sound's frequency, the shorter its corresponding full cycle sound wave.  Think of sounds, and their corresponding sound waves, as a continuum from long and deep to short and high.  For example a 20 Hz full cycle sound wave is about 56' long and a 20,000 Hz full cycle sound wave is a fraction of an inch long. 
     It's important to know that the longer bass frequency sound waves have omnidirectional radiation patterns and the much shorter midrange and treble frequency sound waves have highly directional radiation patterns.  It's also important to realize that the longer, omnidirectional sound waves/tones, typically below about 80 Hz, are not localizable (individuals are able to determine their specific position in space) by humans and that the much shorter, highly directional sound waves/tones, typically from about 80 Hz up to 20,000 Hz, are highly localizable by humans, and progressively more easily as the frequency increases.
     In addition, there are some peculiarities in how we humans perceive sound and sound waves:

- We don't even perceive a sound as existing at all until our ears detect a full cycle sound wave at a specific frequency, our brains process the input from the ears and the brain creates the perception of the sound at that frequency. Anything less than a full cycle sound wave being detected, results in no sound being perceived. 
      This fact becomes especially important with bass perceptions in a finite room, since some full cycle deep bass sound waves may exceed the dimensions of the room.  This requires the sound wave to bounce or reflect at least once off of a room boundary (floor, ceiling or wall) before the full cycle bass sound wave exists in the room, is detected by our ears, processed by our brains and the perception of a bass tone at a specific frequency is created.

- Since we generally can't localize bass frequency sounds below about 80 Hz, we perceive all bass below about 80 Hz as mono, which means no true-stereo deep bass exists below about 80 Hz.
     I stated no "true-stereo deep bass" because we are capable of perceiving a form of stereo deep bass thanks to our amazing brains. Our brains are able to perceive a fundamental deep bass tone below 80Hz,  often reproduced by a sub and unlocalizable, as mono and perceive the fundamental deep bass tone's natural overtones or harmonics, which often extend beyond 80 Hz, are often reproduced by the main speakers and are localizable, in stereo. 
     Our amazing brains are then capable of associating the mono fundamental tone with the stereo overtones or harmonics and localize the deep bass tone.  The result is a form of stereo deep bass that I believe needs to be distinguished as something other than "true-stereo deep bass".  For you, this means you can incorporate a sub or subs in your system and you still perceive a stereo sound stage illusion that is equal to, or more likely better than, your current one.

     The next facet of acoustic sound physics it's useful to understand is that all sound waves, at all frequencies, launched into your room by either speaker or sub drivers will travel outward and continue to bounce or reflect off of room boundaries (floor, ceiling and floor) until they are absorbed or diffused/scattered by acoustic room treatments, run out of energy and naturally decay or they collide with another sound wave.   
     Whenever these sound waves collide with each other, it creates what's called a "room mode" at the specific room location of the collision.  These room modes/collisions happen all the time with midrange and treble frequency sound waves and, in an untreated room, are normally perceived as 'airiness' or 'liveness' qualities, which many individuals perceive as enjoyable. 
     However, these midrange and treble room modes/collisions also negatively affect tonal accuracy, stereo details and stereo imaging.  But these midrange and treble room modes affects can be reduced, mitigated and controlled to an extent through strategic deployment of sound wave absorbing and diffusing acoustic room panels/treatments. 
      These room modes/collisions happen often with bass frequency sound waves, too. In an untreated room, however, bass room modes are normally perceived as bass overemphasis (a bass peak),  bass underemphasis (a bass dip) or even a bass cancellation (a bass null).
      But these bass room modes affects are much more difficult to reduce, mitigate and control than midrange and treble room modes.  The required bass trap room treatments are larger, more expensive and can't always be aesthetically placed at the specific room position they're services are needed. 
     Okay, the preliminary topics have been covered on this tome, and it's finally time for me to tie this whole thesis together and get to my recommendations for your specific circumstances.
     Yes, I could have saved  a lot of my time and yours by just stating I agree with atmasphere's earlier suggestion of the Audio Kinesis Swarm 4-sub distributed bass array (DBA) system as an ideal solution but I thought it was more valuable with you having a good understanding for my reasoning for my suggestion.  Here's an Absolute Sound review of the AK Swarm system that gives a very good description of what to expect:

 https://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/

     I use the very similar AK Debra 4-sub DBA in my system/room and can state with certainty, if you have the available room space for four relatively small (1'x1'x2') subs in your room, that you'll be amazed by the near state of the art bass performance of this relatively affordable ($3,200) complete kit bass system.  It's attractive in your choice of woods, the subs would be positioned around the perimeter of your room and are easily concealable and the bass integrates seamlessly with virtually any pair of main speakers. 
     I also believe your very high quality main speakers deserve an equally high quality 4-sub DBA system.  I think you could probably come close to the Swarm's performance by utilizing a pair, of properly positioned and configured, high quality subs.  However, the very good bass would be restricted to a single designated listening position rather than throughout your entire room with the Swarm and the Swarm will likely cost a few thousand dollars less as well as being easier to set up and configure. 

Best wishes,
   Tim

noble100
thanks so much. awesome

so maybe setting up the speaker settings to large (rather than small) makes more sense so that it completely opens up the main speakers. Why bother restricting bass on mains, and then set the subwoofer separately via settings on back of cabinet..

The sub array setup may have merit in a larger room. My room is 12 x 16 with 7 1/2 ceilings. The extremely large asw 2000 from b&w with 12 inch driver set lower would seem more than adequate. I do need acoustic panels.

Hello emergingsoul,

     Are you using an audio/video receiver to power your main speakers?  If so, yes you should set the front l+r speakers (your 804Ds) to "large" so they run fullrange.  Why do you have them set to "small"?
     You should also connect your asw 2000 sub to the "sub out" or "LFE" output on the back of your A/V receiver and optimally position your sub in your room, and in relation to your listening seat using the 'sub crawl method (google it). 
      Then adjust the volume, crossover frequency and phase controls on your sub until the bass sounds best to you.  The goal is to set the sub's volume and crossover frequency as low as possible while the bass still sounds very good to you.  
      Give this a try and report back with your impressions.

Later,
 Tim   

Having heard and loving the sound of B&W, always hearing that they do produce the amount of bass they say they do:

there is no way I would add a sub to those speakers

except

IF I felt the PORT was a bit muddy,  then sending low bass to self-powered sub only; thus out of both the main amp and speakers, might be preferred, that is what I suggest you listen for.

IF I was trying to fill a too large space with low bass.