In the last episode, I determined that the 100 Hz crossover frequency between the SVS subwoofers and the Acoustat panels was too low, because front wall cancellation reflections appear to be centered around 110 Hz or so. (One friend wants me to investigate the reflections further, from multiple angles, etc., but I'm satisfied my story is essentially correct. 100 Hz can't and won't work.)
Early indications were a crossover frequency of 140 Hz might work. I first set up a highpass at 147, but a lowpass remaining at 100 because it seemed to have an approximate 140 Hz acoustic rolloff anyway.
I was troubled by that assymmetry for various reasons. When I ultimately go to linear phase crossovers, such an approach might not work at all. And even more immediately, it seemed that I was still suffering a depression around 100 Hz anyway, just like before.
I was thinking of setting up my fancier measurement rig with calibrated microphone and ARTA to first do a full analysis of the subwoofer response, and the panel response, and find the exact best crossover frequency from that.
But instead, after a day of distraction, I decided to go ahead and try setting both sides to 140 Hz, with normal 24dB/octave, and see how that worked.
And of course, once I had done that, I couldn't help but keep fiddling with parametric EQ's on the subwoofer side to get it straightened out.
(Plot spoiler: I looks indeed like I will have to go back and determine the actual Subwoofer response after all, because it seems to be a factor in how the 140 Hz crossover works. There is considerable weakness around 180 Hz which may be caused by subwoofer already starting to roll off where the crossover is still expecting some output from the sub side. Curiously this only seems to happen in the left channel. I'm thinking the left subwoofer, which is very hard to get behind, may have some sort of internal crossover enabled which is interfering with my attempt to do a good 140 Hz crossover. This needs to be checked by playing the sub with a much higher crossover like 300 Hz. In past experience, it's not good to play pink noise full range into my SVS without any subwoofer. That generates scary sounding noises that make you wonder if the subwoofer isn't going to self destruct. So it needs some crossover, or some other way of ensuring that all testing is below about 300 Hz.)
After first setting up 140 Hz for both the panels and the subs in my miniDSP OpenDRC's I measured what looked like much higher bass than before:
My first impression was that the subwoofer level was too high. (I had long suspected this.) But I quickly took a look at the sub response by itself, but with the 140 Hz crossover enabled). That looked like this:
That looked like there might be some peaking at 140 Hz, but not enough to explain the huge bulge at 140 Hz. So I turned the sub level down and down. From -3dB to -13dB. That looked a little flatter, but there was still that peak at 140 Hz! If I remembered correctly, I already had a big cut there. At that point, not remembering that I had an hour earlier turned down all the PEQ's above 90 Hz on the principle this would be a whole new EQ game because of the new crossover, and I'd best start from scratch. As a result of that memory failure, I started with a huge sub level change rather than first restoring the old EQ's. With a 10dB reduction, the last LF plateau around 32 Hz was clearly lower than the 18kHz peak on top, and generally I like those more-or-less at the same level, intuitively and otherwise (though the true HF response is not revealed by these or any other measurements I have yet done, and on ARTA with my calibrated mike the HF peak appears to be about 15dB higher, which I think partly has to do with my cal microphone's lack of omnidirectionality at those frequencies, or some such factor, even perhaps the way the software works. I think for an RTA long term average type response, it's hard to beat the iPhone running the RTA app I have, and the iPhone simulates a true omnidirectional microphone response with two microphones and sophisticated internal processing.)
Finally I realized I had previously zeroed out the 125 Hz notch and even a 105 Hz notch I had zeroed out last week or before, but left in the PEQ list set to 0dB. I actually took the time to run the oscillator and retune all 3 points. And then back to the RTA and back to the oscillator. I slowly raised the subwoofer level as seemed to work best, but not back to the original -3dB which may indeed have been too high.
(Having the sub level too high, or a substantial "room curve," is very destructive to transparency across the audio range, and also limits dynamic range. You can't turn the level up too far without everything in your house rattling, or even the sub itself sounding off, on very bassy music. You can sort of make a too high level work by having deep notches at the room modes. Or you can lower the sub level and use less-deep notches. It's never exactly clear where the optimal point is between deeper notches vs lower sub level.)
Finally, after endless adjustment, I got to this:
The deepest bass up to just pass 125 Hz is as flatter and nicer than it has ever been. There is zero notch at 100 Hz, though a slight depression that includes 90 Hz. But look, now there are some too-large depressions starting at 160 Hz, and also just above 250 Hz, that I didn't recall from before. I tried fixing the lower one with as much as 7dB boost at 170 Hz without much success. If I remember correctly, the measurement above is the one with the boost already added, it looked even worse before. I figure the boost is OK because at 140 Hz response is already rolled off by 6dB by the 140 Hz crossover, and the fairly high q peak I'm adding at 170 Hz doesn't much extend that low. I generally have more headroom in the bass too, meanwhile the midrange headroom is deliberately limited so as not to waste digital dynamic range and "information"...it's always playing close to 0dB.
(This kind of tradeoff is called "gain structure.")
Still, even with the boost, I'm not happy with this response as it looks. I think it sounds OK, with much punchier bass than before, and the pair of lower midrange depressions aren't immediately obvious to me. On oscillator sweeps they don't sound so much like the null at 110 Hz I was aiming to eliminate with these changes, they sweep better than they look in the RTA.
Early indications were a crossover frequency of 140 Hz might work. I first set up a highpass at 147, but a lowpass remaining at 100 because it seemed to have an approximate 140 Hz acoustic rolloff anyway.
I was troubled by that assymmetry for various reasons. When I ultimately go to linear phase crossovers, such an approach might not work at all. And even more immediately, it seemed that I was still suffering a depression around 100 Hz anyway, just like before.
I was thinking of setting up my fancier measurement rig with calibrated microphone and ARTA to first do a full analysis of the subwoofer response, and the panel response, and find the exact best crossover frequency from that.
But instead, after a day of distraction, I decided to go ahead and try setting both sides to 140 Hz, with normal 24dB/octave, and see how that worked.
And of course, once I had done that, I couldn't help but keep fiddling with parametric EQ's on the subwoofer side to get it straightened out.
(Plot spoiler: I looks indeed like I will have to go back and determine the actual Subwoofer response after all, because it seems to be a factor in how the 140 Hz crossover works. There is considerable weakness around 180 Hz which may be caused by subwoofer already starting to roll off where the crossover is still expecting some output from the sub side. Curiously this only seems to happen in the left channel. I'm thinking the left subwoofer, which is very hard to get behind, may have some sort of internal crossover enabled which is interfering with my attempt to do a good 140 Hz crossover. This needs to be checked by playing the sub with a much higher crossover like 300 Hz. In past experience, it's not good to play pink noise full range into my SVS without any subwoofer. That generates scary sounding noises that make you wonder if the subwoofer isn't going to self destruct. So it needs some crossover, or some other way of ensuring that all testing is below about 300 Hz.)
After first setting up 140 Hz for both the panels and the subs in my miniDSP OpenDRC's I measured what looked like much higher bass than before:
My first impression was that the subwoofer level was too high. (I had long suspected this.) But I quickly took a look at the sub response by itself, but with the 140 Hz crossover enabled). That looked like this:
That looked like there might be some peaking at 140 Hz, but not enough to explain the huge bulge at 140 Hz. So I turned the sub level down and down. From -3dB to -13dB. That looked a little flatter, but there was still that peak at 140 Hz! If I remembered correctly, I already had a big cut there. At that point, not remembering that I had an hour earlier turned down all the PEQ's above 90 Hz on the principle this would be a whole new EQ game because of the new crossover, and I'd best start from scratch. As a result of that memory failure, I started with a huge sub level change rather than first restoring the old EQ's. With a 10dB reduction, the last LF plateau around 32 Hz was clearly lower than the 18kHz peak on top, and generally I like those more-or-less at the same level, intuitively and otherwise (though the true HF response is not revealed by these or any other measurements I have yet done, and on ARTA with my calibrated mike the HF peak appears to be about 15dB higher, which I think partly has to do with my cal microphone's lack of omnidirectionality at those frequencies, or some such factor, even perhaps the way the software works. I think for an RTA long term average type response, it's hard to beat the iPhone running the RTA app I have, and the iPhone simulates a true omnidirectional microphone response with two microphones and sophisticated internal processing.)
Finally I realized I had previously zeroed out the 125 Hz notch and even a 105 Hz notch I had zeroed out last week or before, but left in the PEQ list set to 0dB. I actually took the time to run the oscillator and retune all 3 points. And then back to the RTA and back to the oscillator. I slowly raised the subwoofer level as seemed to work best, but not back to the original -3dB which may indeed have been too high.
(Having the sub level too high, or a substantial "room curve," is very destructive to transparency across the audio range, and also limits dynamic range. You can't turn the level up too far without everything in your house rattling, or even the sub itself sounding off, on very bassy music. You can sort of make a too high level work by having deep notches at the room modes. Or you can lower the sub level and use less-deep notches. It's never exactly clear where the optimal point is between deeper notches vs lower sub level.)
Finally, after endless adjustment, I got to this:
The deepest bass up to just pass 125 Hz is as flatter and nicer than it has ever been. There is zero notch at 100 Hz, though a slight depression that includes 90 Hz. But look, now there are some too-large depressions starting at 160 Hz, and also just above 250 Hz, that I didn't recall from before. I tried fixing the lower one with as much as 7dB boost at 170 Hz without much success. If I remember correctly, the measurement above is the one with the boost already added, it looked even worse before. I figure the boost is OK because at 140 Hz response is already rolled off by 6dB by the 140 Hz crossover, and the fairly high q peak I'm adding at 170 Hz doesn't much extend that low. I generally have more headroom in the bass too, meanwhile the midrange headroom is deliberately limited so as not to waste digital dynamic range and "information"...it's always playing close to 0dB.
(This kind of tradeoff is called "gain structure.")
Still, even with the boost, I'm not happy with this response as it looks. I think it sounds OK, with much punchier bass than before, and the pair of lower midrange depressions aren't immediately obvious to me. On oscillator sweeps they don't sound so much like the null at 110 Hz I was aiming to eliminate with these changes, they sweep better than they look in the RTA.
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