Wow this has turned into a great thread. I was a little concerned about it going off the rails early on, but it hasn't.
Thanks to everyone who has chimed in so far and keep the ideas coming.
My take away so far is mostly derived from an earlier post from Audiokinesis:
1 - Get the room as 'tuned' as possible using conventional bass traps and treatments.
2 - Then, utilize one or both of EQ/DSP and DSA to dial-in the best response. As Duke says, smooth bass = fast bass.
Then things get a little more subjective around the following:
1 - Time-alignment is a non issue due to low frequency wavelengths. I can see the physics of this argument yet there are others in the know who disagree. Lyngdorf for example (The TACT spinoff) factor for sub positions and have a delay factor for the mains built into their DSP or 'Room Perfect'. Perhaps that's a novelty or selling point and nothing more. I don't know.
2 - Phase control. Is it an issue or isn't it an issue? In my OP I was asking whether or not DSP factors for phase alignment and the consensus has been that it does not. Some of the more upmarket subs have 360 degree control where others simply have a 0-180 toggle. REL, known for their 2-channel prowess offer neither on their T/7i, which is aimed at the 2-channel market. So what gives? I suppose their answer would be to flip the leads on the amp binding posts. (high level)
My choice of the word 'phase' when describing a specific issue was perhaps misleading. Maybe it's a phase issue maybe it's something else.
Just to describe the problem a little more fully -
I have my mains about 75 inches from the front wall and with the mains only I get an excellent perspective, sense of depth and space, and very focused imaging. By perspective I mean that the soundscape is almost entirely behind the front plane of the speakers and extends through the front wall and beyond the outside boundaries of the speakers. The bass from the Dunlavy, in my room, is poor in two ways. Using a test CD and SPL meter, the extension from the sealed box speakers is good into the 45hz range then rolls off quickly. There are dips around 70-130Hz, again at 150-170Hz. I can clearly hear those on certain tracks.
Adding a pair of subs on the outsides of the mains, about an inch or so forward, helps to flesh out the bottom end and mid-bass, but the subs are obviously affected in the same way as the mains by the room modes and the frequency response anomalies.
So it's still far from ideal, but - the attractive imaging and soundstage properties are maintained. There's no negative effect. There's a positive effect but it isn't 'problem solved'.
So moving the subs and placing them by ear/test to get the best and smoothest response at the listening position I end up with the right channel sub about 2 feet behind the right main and the left channel about 5 feet in front of the left main, both up against side walls, both well away from corners and neither firing directly into a wall!
In this way I get a smoother response all the way through the frequency range. Not perfect but better. However, the depth and width of stage is diminished and I lose the laser-like focus of images in the soundscape. There's almost a smearing affect where the air and space around images diminishes and that's what I'm referring to as a 'phase anomaly'.
I've moved the mains to and fro ad nauseam, as we do. I can get a little better response closer to the front wall but the perspective and depth is diminished and I don't want that.
I've tried different listening seat positions, obviously.
I've tried sub placement all over the room and messed with phase toggles (0 or 180) and right now I seem to have the best compromise. But I'm not entirely happy with it.
So if the above is something other than a phase issue I'm happy to stick a new label on it and I'm all over any ways to fix it that don't involve bringing in more gear!
Since posting this thread I've written to a couple sub manufacturers to see if they'd come up with some comments and perhaps even loan out a quad of subs so I can set up the DBA and write the process up as a review. I doubt that will go anywhere but plan B is to go out and buy two or four subs on the used market.
All of your comments are helping and my trigger finger is twitching, but I'm not quite ready to buy more subs just yet.
Thanks to everyone who has chimed in so far and keep the ideas coming.
My take away so far is mostly derived from an earlier post from Audiokinesis:
1 - Get the room as 'tuned' as possible using conventional bass traps and treatments.
2 - Then, utilize one or both of EQ/DSP and DSA to dial-in the best response. As Duke says, smooth bass = fast bass.
Then things get a little more subjective around the following:
1 - Time-alignment is a non issue due to low frequency wavelengths. I can see the physics of this argument yet there are others in the know who disagree. Lyngdorf for example (The TACT spinoff) factor for sub positions and have a delay factor for the mains built into their DSP or 'Room Perfect'. Perhaps that's a novelty or selling point and nothing more. I don't know.
2 - Phase control. Is it an issue or isn't it an issue? In my OP I was asking whether or not DSP factors for phase alignment and the consensus has been that it does not. Some of the more upmarket subs have 360 degree control where others simply have a 0-180 toggle. REL, known for their 2-channel prowess offer neither on their T/7i, which is aimed at the 2-channel market. So what gives? I suppose their answer would be to flip the leads on the amp binding posts. (high level)
My choice of the word 'phase' when describing a specific issue was perhaps misleading. Maybe it's a phase issue maybe it's something else.
Just to describe the problem a little more fully -
I have my mains about 75 inches from the front wall and with the mains only I get an excellent perspective, sense of depth and space, and very focused imaging. By perspective I mean that the soundscape is almost entirely behind the front plane of the speakers and extends through the front wall and beyond the outside boundaries of the speakers. The bass from the Dunlavy, in my room, is poor in two ways. Using a test CD and SPL meter, the extension from the sealed box speakers is good into the 45hz range then rolls off quickly. There are dips around 70-130Hz, again at 150-170Hz. I can clearly hear those on certain tracks.
Adding a pair of subs on the outsides of the mains, about an inch or so forward, helps to flesh out the bottom end and mid-bass, but the subs are obviously affected in the same way as the mains by the room modes and the frequency response anomalies.
So it's still far from ideal, but - the attractive imaging and soundstage properties are maintained. There's no negative effect. There's a positive effect but it isn't 'problem solved'.
So moving the subs and placing them by ear/test to get the best and smoothest response at the listening position I end up with the right channel sub about 2 feet behind the right main and the left channel about 5 feet in front of the left main, both up against side walls, both well away from corners and neither firing directly into a wall!
In this way I get a smoother response all the way through the frequency range. Not perfect but better. However, the depth and width of stage is diminished and I lose the laser-like focus of images in the soundscape. There's almost a smearing affect where the air and space around images diminishes and that's what I'm referring to as a 'phase anomaly'.
I've moved the mains to and fro ad nauseam, as we do. I can get a little better response closer to the front wall but the perspective and depth is diminished and I don't want that.
I've tried different listening seat positions, obviously.
I've tried sub placement all over the room and messed with phase toggles (0 or 180) and right now I seem to have the best compromise. But I'm not entirely happy with it.
So if the above is something other than a phase issue I'm happy to stick a new label on it and I'm all over any ways to fix it that don't involve bringing in more gear!
Since posting this thread I've written to a couple sub manufacturers to see if they'd come up with some comments and perhaps even loan out a quad of subs so I can set up the DBA and write the process up as a review. I doubt that will go anywhere but plan B is to go out and buy two or four subs on the used market.
All of your comments are helping and my trigger finger is twitching, but I'm not quite ready to buy more subs just yet.