Subwoofers and Phase Question For You Sub Experts

Playing with phase settings has little impact on the problem since there’s just a toggle for 0 and 180

This is not phase. This is polarity.

Some of the more upmarket subs have 360 degree control

This is phase. This basically helps to achieve maximum output level of the subs.

but the subs are obviously affected in the same way as the mains by the room modes and the frequency response anomalies.

 Multiple subs helps with this issue.

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'.

 This could be caused by an overlap in frequencies being produced by your mains and your subs. This is an issue that a crossover or speaker management system can eliminate. If you do not want to do an external crossover set the low pass filter on your subs to the low end cutoff point of your mains. Plugging any ports should also help.

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.


    

     Okay, I'm back and have more time now, so I'll just pick up where I left off in my last post.
     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 and you're mainly concerned with just good bass response at your listening seat and not throughout your entire room, which would require a 4-sub DBA system.  I recommend you use the crawl method to optimally locate each sub around the perimeter of your room. Here's how to perform the crawl method:


1.  Disconnect your 3C speakers, hook up one of your HSU subs and place it at your listening seat position.

2.  On the HSU sub, set the volume control at 50%, the crossover frequency at 60 Hz and the phase at 0 (in-phase).  Play some music with good and repetitive bass.

3.  Beginning at the right front corner of your room, slowly begin walking in a counter-clockwise direction around the perimeter of your room, listening carefully for the exact spot at which the bass sounds best to you (solid, powerful, accurate, detailed, dynamic and natural).  Take your time, walk or crawl on your hands and knees very slowly, listen very closely and repeat if necessary until you identify the exact spot.

4.  Once the spot is identified, move the HSU sub to this exact position.
5.  Repeat this process for your second HSU sub but just begin searching slowly for the next exact room perimeter spot the bass sounds best to you, from where the first sub was located.

6. Once the second spot is identified, move the second HSU sub to this exact position. 

7.  Replay the same music, sit at your listening seat and verify the bass sounds very good to you.  If it does, proceed to step#8.  If it does not, you need to redo the entire procedure starting at step#1. 
8.  Reconnect your 3C main speakers but reverse the polarity on each speaker by connecting the pos. wire to the neg. speaker terminal and the neg. wire to the pos. speaker terminal.  NOTE: Make sure you reverse polarity only on the speakers and not on the amps.  Play the same music and set the phase control on both subs to the position at which the bass sounds the worst to you (the least solid, powerful, accurate, detailed, dynamic and natural).  The reason the polarities are reversed on the main speakers for this step is because it's normally easier to identify the worst bass response in a room than it is to identify the best, it's just a useful trick.  Reconnect your 3C speakers as normal and in-phase, pos. wire to pos. speaker terminal and neg. speaker wire to neg. speaker terminal.
9.  The final step is to fine tune both of your subs by optimally setting the volume and crossover frequency controls on each sub, one at a time. For best results, I recommend setting both controls as low as possible with the caveat that the bass overall still sounding very good to you at your listening seat. It's very useful to recruit a volunteer for this final step, who can slowly adjust the controls at your direction from your listening seat.  Of course, you're free to set these controls at whatever settings you prefer but, based on my knowledge and experience, setting each of them as low as possible typically provides the best results in terms of seamless integration, accuracy, details and a general sense of ease and naturalness on all bass content.  

     Strictly following this procedure should ensure that your listening seat is not located at a bass peak, dip or null in your room and vastly improve the overall perception of bass response performance from your listening seat. I believe your previous sub positioning arrangements likely resulted in your listening seat being positioned at a bass dip or null in your room.  It's very important that you position each sub at the exact position each sounds best from your listening seat, even if that means rearranging your room décor a bit to accommodate optimum positioning.  
     Poor bass response performance is often the result of individuals, or their significant others, wanting to position the subs where they look the best, are the most convenient or are the most out of the way, rather than where they perform best.  It's just like everything else in audio, a matter of choices and compromises.


I hope this will help you,
       Tim