Rooze:
"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."
Hello Rooze,
I think your comments above are a very good summary of your concerns and goals. Basically, you'd like the already very good soundstage illusion created at your listening seat by your Dunlavy 3C main speakers in the midrange and treble regions, what you call "perspective", to be equally good in the bass region. You've been attempting to achieve this by incorporating two good quality HSU subs in your system and room, at various positions and configurations, with less than desired results. I believe this is the crux of your matter, but please correct me if I've misunderstood.
If not, my opinion is also that your issues are not phase related. I believe they are instead sub positioning and configuration related. I'm not surprised that you're having bass issues since it's highly unlikely that the optimum positions of your pair of 3C speakers, in relation to your listening seat, for midrange/treble and imaging performance are the exact same optimum positions of your pair of 3C speakers, in relation to your listening seat, for bass performance. The real problem is that the position of your system's bass drivers (woofers) in your room are restricted to being located directly below your system's midrange and treble drivers in your room.
As I stated earlier, bass frequency soundwaves behave very differently than the much higher midrange and treble frequency soundwaves in any given room. This is mainly due to the fact that full cycle bass frequency soundwaves are very long and have omnidirectional radiation patterns while full cycle midrange/treble frequency soundwaves are much shorter and have very directional radiation patterns. As a result, the perception of bass and midrange/treble at one's listening seat is facilitated and can be optimized when the positions of their corresponding drivers are independent of each other and can be located in the room separately.
The above is why I prefer to treat my systems as two systems: a bass system and an everything else system. I typically begin by optimizing the bass in the room first because I think it's usually the hardest to get sounding right in most rooms and then optimize the everything else, which includes midrange/treble and imaging performance, afterward because it's relatively much simpler. I suggest you may want to try doing the same.
In your case, this would entail a couple of possible options as solutions. Based on my knowledge and experience, I know that utilizing either an Audio Kinesis or a custom 4-sub DBA (distributed bass array) system would provide the highest quality bass response and integration in virtually any room and with any pair of main speakers. I believe this is the ideal solution for you because it will work extremely well for your system now as well as if you ever change rooms or main speakers.
However, I realize you already own two good quality subs which I also know should work well if the subs are properly located and configured. I recommend you use the crawl method to optimally locate each sub around the perimeter of your room. I can describe this, as well as how to optimally set the volume, crossover frequency and phase controls on each, later if you're interested. Sorry I don't have time right now.
