In my medium room placed near a wall, the 8361A's each have a massive +20db mountain of boost in the bass region. In-room response does not roll off until 25hz in my medium room, and I'm quite sure could easily reach 20hz in a small room. Due to room gain, the bass is overwhelming and of course not flat FR until equalization. After equalizing flat, and then adding back a nice (now smooth) bass boost and treble attenuation to taste (which in my experience when done carefully, solves
all potential complaints of harshness or brightness others may mention), they sound pretty incredible as full-range speakers without a subwoofer.
The main difference you'll see vs bigger tower speakers (e.g. Revel F328Be Salon2's etc.) with significantly more woofer swept volume is that the Genelec 8361A's frequency response rolls off
extremely quickly like a cliff at the lower end (which is extended a bit in depth with room gain, but not massively). Whereas these big towers, and also if you use a subwoofer, tends to fill in the sub-bass more. Whether this is audible or not is up to you to decide, but you can always add a subwoofer to fill in the bottom section and the 8361A will still give you the benefit of much much greater power in the 100-500hz region, which I find is actually quite important for that 'tactile' bass feeling.
In fact, I would say that having used
dual 18" subwoofers + speakers with unexceptional midbass capabilities in the past (I won't name names as I do think they're great speakers for what they are), even with the subs are crossed over at 80hz or 120hz, the feeling of immense bass power
is still nothing like the feeling you get with even a single pair of Genelec 8361A's and no subwoofer!
The only scientific explanation for this I can think of is that
there's something extremely important in the 100-500hz range to deliver that sensation of what many describe in a variety of ways (impact, slam, tactile bass, etc.) Both low distortion and high SPL capability here is essential for this, depending on your listening level. So I suspect you'd only match the powerful sounds of speakers like the 8361A with less powerful woofer speakers if you cross the subwoofer(s) at 200hz-500hz+, and this is only going to sound good with stereo subwoofers physically co-located with your mains (since 200-500hz is quite localizable)!
It makes sense if you think about it; consider a drum impact waveform with a deep fundamental frequency; if you only play the fundamental frequency, the time-domain signal will just look like a smooth sinewave. If you incorporate the higher harmonics of the drum impact, the time-domain signal will be much sharper, and deliver a much higher pressure and abrupt 'leading edge' of the wave. Sorry for my hand-wavey terminology, but hopefully this makes sense.
To those who say "we can't hear time-domain though"; perhaps... but can we
feel it (10-500hz)? I suspect we might. But even if we can't, I'm not even talking about phase alignment; I'm referring to dynamic compression and nonlinearity; if your subwoofer can do 106db from 20-100hz, that's all great, but not very useful if your main speaker can't maintain 106db at the crossover point, because if it can't, you'll get weird compression artifacts and possibly all sorts of unpleasant destructive interference patterns as the dynamic compression occurs in the main bass drivers but NOT the subwoofers!
And before you say "106db is so loud!" Yes it definitely is, but depending on the frequency of tone and the size of your room etc., it's not nearly as loud as you think for the
bass frequencies. In upper mids/treble, you'll probably never want to go above high 90s dbA. But in the lower frequencies, we hear very differently (see dbA vs dbC weighting).