The last few Left Boosts

On September 3rd I finally got to sweeping the left channel relative depression from 140-200 Hz.  It's higher than the 1khz level, I simply believe (that's all it is) that the elevated bass plateau should extend to about 200 Hz, not end abruptly at 140 Hz which is just past the crossover frequency.

Sweeping revealed depressions centered at 151 Hz and 182 Hz.  Thinking that 151 Hz would work better (I have only one PEQ left so I can't do both) when I set a boost at 151 which produced an abrupt and deep depression at 180 Hz, which wasn't much better (if any) looking than with no boost.

Left, boost at 151 Hz

Boosting at 182 Hz seemed to work better.  I could get a nice smooth decline from the bass plateau through 180 Hz, a slight relative peak at 200 Hz, and thence to the midrange floor.

Left, boost at 182 Hz

By various methods I tried to reduce the minor peaking at 200 Hz.  I tried narrowing and widening the boost, which resulted in less regular looking curves.  I tried moving the depression-centered 182 Hz boost down lower to an arbitrary165 Hz (the curve barely looked different from 151 Hz boost).  Making the boost smaller didn't help either.  So I stuck with a +6dB boost at 1/2 octave, which gave the relatively smooth looking curve shown.  180 Hz is still a depression (but much less so) even being boosted by +6dB and I don't go higher than that.  The curve would look even better perhaps if I raised it to about +10dB.

A few little peaks and depressions are inevitable.  So I've decided on the 182,1/2,+6 version of the boost and to move on to the correcting the 90 Hz depression (which means I need to switch the chairside DEQ to handling the subs, for which a new optical cable just arrive so I can more easily switch back and forth).

It's curious that there seems to be a relative depression around 182 Hz (although perhaps this is simply a function of my crossover and desired room curve) and also at 91 Hz.  Perhaps...they are related.

91 Hz could be floor-ceiling bounce, with 182 being the 2nd harmonic.  It's hard to know exactly what my effective ceiling height is because it's slightly vaulted.  However 9 feet, which is twice the wavelength of of 180 Hz, is right in there, that's about the maximum.

My floor is already carpeted.  Possibly critical damping suspended from the ceiling vault would help.  I can hardly imagine the expense and effort involved...

I hooked the chairside DEQ to the sub DAC and began sweeping the 90 Hz depression.  It seemed quite narrow, but giving it a very narrow boost didn't help much.  No matter how narrow I made the boost, the peak at 100 Hz was still there.  I also lightened up a bit on the notch filter at 84 Hz because 80 Hz was also measuring depressed.  (Funny it doesn't much sound that way).

A key problem was keeping the 100 Hz peak from rising up which it wanted to do at the slightest provocation.  By finessing the level, Q, and slight frequency (I actually started from 92.5 Hz where the audible depression was greatest, and rolled back slightly to 90.3 because it kept the 100 Hz from peaking too much and also helped raise the 80 Hz, which should not have been measuring depressed.  With the right settings I could get 100 Hz to be right in line with the lower bass.

Then I worked the bottom of the spectrum.  I wasn't sure where to boost, to raise the entire affected area from the center I'd have to boost at 26 Hz or so.  I first tried 31 Hz, that produced a depression at 35.  Thinking if I moved the boosting farther away it wouldn't intereact, I tried 26, and, as I should have expected, the depression at 35 Hz simply got bigger.  Finally I decided to boost right at 35 Hz, the center of the depression (in both channels!) and accept the fact that it wasn't going to boost 20-22 Hz enough.  (This channel stimulates whole house resonances from 15-20 Hz so a bit of low frequency rolloff is not a bad idea anyway.  It stimulates them best of all because the sub is in the corner of the entire house.)

After a few hours of sweeping, adjusting, and measuring I came up with a boosted response that looks pretty good, I think.

Left channel with 35 and 90 Hz boosts

Left Sub PEQ's

The fact that the bass plateau is as high as it is follows from actual listening in which the bass sounded weak unless at that level.  I think it's because the brain DOES compensate, though not perfectly, for the room gain.  It expects that room gain to be there, and if you've sucked out all the peaks, the bass sounds weak even if it measures flat.  The brain does NOT compensate perfectly for the actual room mode peaks, so it does help to suck them out, but you then need to add compensatory gain to the entire area.

I'm not how high in frequency the boosted area should go.  I've been thinking 200-250 Hz, but it might be lower.  With my current setup, I can dial back the panel boost at 182 Hz and this pretty much changes the room curve turnover point from 200 to 160 Hz.

I think I forgot to report an intervening listening session, in which AFTER I had dialed everything down for the last time, and both channels had about the same room curve, the bass sounded weak, so I dialed it up another couple dB at the sub DAC.  The new sub DAC level is -5.5dB.  I was unsure if I should set it that high, perhaps it would have been better to lower the attenuation on the subs, which itself is pretty high.  I can't seem to find any specs for the line inputs to my subs (and they have different generations of plate amplifiers too) but I'd think the DAC level of 2V would be ok, though to play it safe I liked to keep the DAC level at -6 or greater, which I'm now violating slightly.  I'd be certain that a level of 1V would be ok into the plate amp because that was the historical home theatre standard level.  Most likely the inputs themselves could take much more, and the latest manual says "professional levels" which would be about 10V.  Of course the sub itself might overload waay before that.

Also now that I've dialed in boosts into the left channel, I may find that the sub level should come down a bit again.  And I haven't even started investigating channel differences in different bands, or just between subs and panels.

While listening to Bass Erotica, I decided to dial down the bass by 1dB, so the DAC is now at -6.5dB.

I'm feeling and thinking that the boosts aren't that good for background listening.   Cuts are ok anywhere, but boosts become annoying where they are not needed.  Perhaps I need to bring back the "Listening Position" EQ with boosts, and Background Music EQ with no (or fewer) boosts, and Movie (which is really dialed back a lot for watching movies in the room perimeter, where the bass is most augmented).  For similar reasons, I originally called the Listening Position EQ "Boost" and I gave it that name in my home EQ system.