My room is 23'x16' with an 8' ceiling. I have some pictures posted on my profile if you want to take a look. It's a combo music and ht system.
I have a 65" hdtv wall mounted to the middle of the front 16' wall with my Magnepans straddling the tv,they're about 8' apart and 3-4' out from the front wall. My listening seat is in the middle of the rear 16' wall. The Magnepans are slightly toed-in and their axis cross at my position.
For serious music listening sessions, I usually move the Magnepans about 5-6' out from the front wall and with no toe-in. I then move my listening seat exactly between them and about 3-6' away from the midpoint between them. I find this positioning allows for an amazingly
three dimensional soundstage illusion on good recordings that is wide, deep, detailed, solid, stable and realistic.
You stated: "To get my former system time-coherent I had to place the Velodyne DD18 a bit in front of the main speakers, if I remember right. Not a good thing, in our living / listening room. Your Debra system seems much more flexible. Happy to hear it works so well. Maybe I could complete my system with half of it - two subs. Although I have neighbours who complain with too much bass."
It makes sense to emphasize the importance of time-coherence of midrange and treble tone frequencies, that is that midrange and treble soundwaves reach the listener at about the same time since these frequencies have soundwaves that are relatively short in length, measured in inches. It makes little sense to include deep bass tone frequencies in this emphasis on the importance of time-coherence, along with midrange and treble tone frequencies, since bass frequencies have soundwaves that are very long, measured in feet. A 20 Hz soundwave is 56 feet long, a 30 Hz is 38 feet long and a 40 Hz soundwave is 28 feet long. Expecting time-coherence of bass, midrange and treble tone frequencies, that is that bass, midrange and treble soundwaves reach the listener at about the same time makes little sense.
Here's a quote from Duke Lejeune, Audio Kinesis owner and maker of the Swarm bass system:
"Another factor is that it takes the
ear a fair amount of time to hear bass
frequencies. The ear cannot even detect the
presence of bass energy from less than one
full cycle, and it takes several cycles to
detect the pitch. So considering the
wavelengths and room dimensions, by the time
we can hear bass tones the room’s effect is
in full swing. Perceptually, in our home
listening rooms there is no such thing as
“direct sound” in the bass region; by the
time we even begin to hear it, it’s all
So, moving a sub in front of the main speakers likely makes little to no difference in the perception of bass response performance in a normal sized room.
I believe 2 subs will begin to provide smoother bass response, roughly twice as smooth as a single sub, but that 4 subs will be roughly twice as smooth as 2 subs.