B&W 805 to 804

In my experience, the size of the speaker doesn't have much to do with how well it performs at low volumes.

I had N804s in my 14x13 room and they worked well although in the end, I wanted more bass extension. In your case, I don't think you will have that problem! The 804S is supposed to have more bass and a bigger sound than its predecessor.

Arthur

If you have a 15' x 15' room, you have bigger problems than choice of speaker!
That being said, the only thing you will benefit from is a more extended low end, but then again, your room will play havoc with that!

Regards,
Bruce

The upgrade will be well worth it. Contrary to popular belief, well designed large speakers do not need to be played loud in order to sound good. It is actually the other way round, they sound so good and lively (transient response) that you can't help the urge to turn them up. Small two way speakers start distorting and compressing much sooner than larger three way speakers and that is the reason nobody likes to crank 'em and you never see these designs in a nightclub.

Another factor is that smaller designs are often intentionally built to sound "big" in the bass at low levels (recall equal loudness curves and that big bass sound in a small box sells speakers - usually a hump between 75 and 100 Hz does the trick but this will sound bloated at higher levels and drown out the lower mid range often with copious amounts of distortion).

Larger speakers tend to be more balanced and therefore sound good at all levels but may require the use of "loudness" or a little bass lift at extremely low levels to match what you are used to hearing from their smaller bretheren.

The upgrade difference will probably be most noticable with better clarity on male vocals...i.e. in the region of lower mid range.