Originally Posted by acribb
Well this appears to be the best I can do in my room. Let me know your thoughts on if there is anything I can improve. Not sure if Ed over on the SVS thread can do anything but i'm open to suggestions from anyone on how to improve the performance above 75hz.
These test results reflect the best I could get from having the subs in the front corners of the room which is where they best fit. I may be able to move the front right sub out from the corner up to 4 feet but it sure won't look pretty. These measurements included fiddling around with the distance post Audyssey and extended and non extended mode.
My initial Audyssey settings created with all ports open mode yielded the Denon 4400 -11dB and -10.5db initial sub trim levels with both subs set to -24dB volume. I then adjusted the sub trim up 5dB landing at -6dB and -5.5dB.
The tests depicted in this graph show extended (green) and non-extended mode (red) at -40MV and a -15 sub volume.
Originally Posted by acribb
I'm only testing LFE with the Timing Reference Output set to L.
The mains are set to small and I moved the crossover from 40 to 60hz post Audyssey set up.
I like the additional low-end SPL you picked-up, using the porting technique I suggested. How does it sound now?
Perhaps like several others reading the thread, I'll admit I'm a little confused at this point, though. If you are only testing the LFE channel, then your crossovers to your speakers don't matter. Once you have done a little more problem-solving with just the subwoofers, I would like to see a combined measurement of subwoofers and speakers, because that will much more closely replicate what you will be hearing. The measurements are much more valuable when we can correlate them to what we can actually hear, and I'm interested in seeing what happens when the subs and speakers are combined.
To that end, I would recommend raising your crossovers to 80Hz, rather than 60Hz, to start with. You can always drop down once you see, and hear, what is happening. But, coming from an AVR setting of 40Hz, I would recommend going up another full octave, to 80Hz. Your speakers will still be playing below 80Hz, but at a reduced volume level, just as your subwoofers will still be playing above 80Hz, but at a reduced level. (It is possible that a 60Hz crossover will work better, in this case, if the subwoofer roll-off above 72Hz persists. But, I would still default to an 80Hz crossover to begin with.)
With respect to the drop-off in the LFE channel, above about 72Hz, adding in your front speakers, or your center channel, won't change that, as the LFE channel is completely independent of the other channels, and has no relationship to your bass-management. If pulling one subwoofer forward a foot or so helps with the >72Hz response, then it might be worthwhile to try it.
You will just need to experiment to find out whether moving one of the subs a little helps. I also wonder whether the relationship between your subs and your listening position is a factor. Try doing some sweeps a foot or so in front of, and behind, your listening position.
If it makes a difference, you might try adjusting your seating a little.
If you really can't fix the roll-off above 72Hz now, though, I'm not sure how much practical difference in your sound the roll-off will actually make. Here is what I mean by that. Although the LFE channel is theoretically designed to play bass frequencies up to 120Hz, several audio experts including Mark Seaton and Roger Dressler (formerly of Dolby Labs) have claimed that there is little meaningful content in the LFE channel above about 80Hz. Several film mixers have confirmed this notion, in some AVS discussion threads, from several years ago.
The LFE channel was created to augment low
-frequency special effects in 5.1 movies. It plays the same low-bass content that the regular channels do, but it plays that content +10dB louder than the regular channels. And, the Dolby/THX standards were always based on an assumed 80Hz crossover from the subwoofers to the speakers. THX-rated speakers are specifically designed to use an 80Hz crossover. So, it makes sense that although the LFE channel can go up to 120Hz (and beyond at a reduced volume level) that the intent of the channel was always to amplify low
-bass frequencies and not just bass frequencies in general. (The LFE channel was also intended to be played exclusively by subwoofers, and most subwoofers play their best, with the lowest distortion, below about 100Hz.)
The idea that there is relatively little meaningful content in the LFE channel (as opposed to random bass noise) above 80Hz, has led many listeners to try setting the LPF of LFE to 80Hz. And, that in-turn, has led many people to try cascading crossovers (explained in Section III-C of the Guide linked below). When cascading crossovers are implemented, the subs are deliberately rolled-off faster above 80Hz, and naturally that roll-off is actually starting below 80Hz
With very few exceptions, the people who have reported trying that technique, on AVS, have reported clearer and somewhat punchier bass, and have chosen to run their HT systems that way. (At least three people I can recall, have preferred to maintain the higher LPF setting in order to have louder sounding bass above 80Hz.) Like everything in audio, it is a YMMV issue, but the bottom line is that a roll-off at 72Hz may not be a disaster, and you may not notice it at all. You just wouldn't need to implement cascading crossovers.
If I were you, I would still experiment a bit to see if I could improve on the overall subwoofer FR above 70Hz. And then, I would also measure to see how things look when you add in the front speakers (or the center channel). That won't affect what happens in the LFE channel, but you still want to know how your subwoofers and speakers integrate with about an 80Hz crossover.
Above all, I would stop and listen periodically, to determine whether there were any audible correspondence to the things I was measuring, and the things I was hearing. That will help you to decide whether you are headed in positive directions, and it will also help you to know how far you want to take your experimentation and problem-solving efforts.