Balancing "Hotseat 2"

I wanted to check the subwoofer and system balances for the new Hotseat position, but ended up doing more.

I couldn't help myself but make a few more adjustments to the left sub EQ.  I deepened the cut at 144 Hz from -4dB to -5dB to remove a bump there.  I lightened the cut at 71 Hz from -8.5 to -7 dB to reduce the depressions in that range.  I lightened the cut at 39.4 Hz from -2.5dB to -1dB to reduce the depression there.

Then I made initial per channel measurements for the left and right.  I was wrong in thinking the right sub was lesser than the left sub, in fact the right sub was greater.  And it was noticable how I had boosted the left sub at 22.4 Hz and not the right.  So I boosted the right sub identically: +4dB at 22.4 Hz.  That gave both channels an identical 20-25 Hz "grunt" And setting the center boost frequency at 22.4 Hz, bandwidth 1/3 octave with amplitude of +4dB seems to evade some subsonic whole house resonances (which cause the glasses in the kitchen to rattle) which appear to be below 20 Hz.  But it makes the measured bass much more flat (the lowest bin in the iPhone "Analyzer" app is 22.5 Hz, so, yeah, you could say I'm adjusting to the app, while I don't like that idea in principle--it would be better to sweep with an oscillator as I have done before).

I was also bugged by the 280 Hz resonance in the right channel, which was visible both in the sub only and combined response.  To nix that, I added a maximum cut of -15dB at 280 Hz, where the right sub shouldn't be playing anything anyway.  That fixed the sub only response (of course) but only partly fixed the combined response, the room apparently amplifies 280 Hz in both.

I noted that the pink noise in the sub only had a very deep sound on the left, but limited in the right.  So I added a boost in the right sub identical to the 20.4 Hz, 1/3 octave, +4 in the left.  That made both subs sound much more similar, with an identical super low frequency grunt.

Despite all these changes, the right channel was +1dB over the left (the boost at 20.4 Hz made no difference at all, thanks to the C weighting).  So I went into the Tact and changed the L/R balance.  (The Tact digital preamp is the only place I can easily make that change, as the Behringer DEQ's frustratingly do not have individual channel gain controls, instead they have a stupid LR image shift which I almost never use.)

Previously I had cut the left channel by an astonishing 2.3dB.  I ultimately changed that to -1.2dB to bring both channels into exact balance, measured with pink noise and C weighting.  The subs alone are pretty chose in balance, with the left (!) measuring -0.2dB lower (not higher, as I had guessed).

To summarize, I changed many things in the right channel sub EQ, and in the Tact channel balance from -2.3dB on the left to -1.2dB.  The result is that both channels measure identical levels with pink noise and the subs nearly identical (0.2dB difference. favoring the right, when I had expected the reverse).

I saved these new "Hotseat" settings and now consider this to be "Hotseat 2".  (I can't keep calling this "New Hotseat" as there will surely be many new adjustments.)

There remains a slight audible difference between left and right.  The right seems to have more mid highs, while the left may have more high highs.  This could have to do with the adjustment of the "HF Balance" controls.  I can easily access the HF Balance control on the left channel (it has a knob in the interface) but I cannot easily access the HF Balance control on the right (it requires moving a bracket inside in interface since it is the later design).  I don't think the difference between interface types is very important because the older one (left channel) was give the "C" mod by a famous Acoustat modifier, and "C" mod was the factory version on the right.  The mod level is what makes the most difference in frequency response.  The fact that the right channel has the "Medallion" transformer and the left channel does not is something I consider to be unimportant in frequency response measurements (the Medallions have better overload characteristics, which is relatively unimportant as I'm crossing over at 125 Hz which keeps the bass transformer from overloading as it often does if you are running the Acoustats full range).

Or it could be that the right channel just fires into a different acoustical space than the left, explaining the difference.

It is incredible how many changes needed to be made since the last "Hotseat" adjustments which were done just last year.  I have only changed the acoustical space slightly because the old recliner chair is no to the immediate right of the listening chair, which is now the Director's Chair.  Perhaps the ceiling Q has changed because of foundation shifting and roof replacement.  I've changed the Acoustat positions only very slightly and the subs none at all.  None of these ideas seems like an adequate explanation.  Perhaps I should run an RTA at least monthly or at least quaterly to be sure the system EQ is still working well.  The new left channel response is pretty smooth, good enough for me to say (as we used to say at Audio Dimension when I worked there) "Ship It!"

Right channel response 10/5/26 Hotseat 2

Left Channel EQ Hotseat 2

Right Channel EQ Hotseat 2

Afterwards I listened to parts of track on "Bass Ecstasy" by Bass Erotica, and "We Want to Be Loved" by Grouse.  The latter sometimes gave me goosebumps and brought tears to my eyes.  THAT's what high end audio is all about.

Adjusting the New Hotseat EQ's

To make more precise measurements, I set up the microphone stand with in the new hotseat position, with the director's chair in place.  The adhoc measurements in October were using the iPhone 16, whereas I routinely use my iPhone 8 on the stand (so I can keep it there).  Comparing iPhone 8 and iPhone 16 on the stand there are no substantial differences (whereas the previous iPhone 16 measurements in October while being hand held are a bit more different).

Left Hotseat, stand, iPhone 8

Left Hotseat, stand, iPhone 16

Left Hotseat, handheld, iPhone 16

When the iPhone was handheld (that measurement was done on October 19) there is somewhat more high frequency loss in the 2k-15k region (which seems reasonable) but about the same (or somewhat less) at 20kHz.

The high frequency loss generally seems to be the result of wide angle with the face of the speakers.  Since they are "aimed" to be off axis slightly in the back of the room there, they are even more off axis in the front.  I can tell as I walk backwards from the hotseat position to the back of the room that the highs are increasing.  The system measures much flatter to 17kHz in the back.

I can't change the angle as it's a compromise between hotseat and back.  Aiming the speakers more towards the hotseat position destroys the imaging in back.  As it is now, the high frequency loss at the hotseat is not objectionable, it might even be musically beneficial.  Voices and acoustical instruments sound "real" and not electronic as they often do with hifi systems.  I also note that it doesn't entirely reflect what the ears "hear" because the ears are closer to being on axis (the microphone is positioned to the center of the head, and not where the ears are), plus the ears are highly sensitive to the sound coming in perpendicular to the ears, which is not as much affected by the angle with the speakers.  So it "sounds" higher from 2-10kHz than it measures.  If I made it flat it would no doubt sound too bright.

I'm not sure this problem warrants "fixing" now by EQ or other means.  If I use EQ, I'd have to start switching panel EQ's between hotseat and back, an additional complication.

The somewhat lumpy bass probably requires a re-do rather than a tweak.  To do it correctly I need to get out the oscillator again and do sweeping, with a remote EQ at chairside to fine tune the PEQ centers and Q to get them just right.  The RTA can be misleading for such fine adjustments.

Unlike in the back of the room, there is no suckout in the midbass between 125 and 250 Hz.  So the panels do not need more boosting there (or, conversely, less sub cuts, I seem to have added rather large subwoofer cuts above the crossover frequency.  These cuts  appear basically fine for the hotseat even if they may be overdone for the back. 

I was going to call it a day, then I noticed something bad.  Right where there is that awful triangular peak at 90 Hz, there is also an apparently outdated boost!  I removed that boost and it rather much smoothed the peak down.

So then, to help fix the depression at 100 Hz, I moved the cut at 108Hz up to 112 Hz, narrowed it slightly, and reduced.

To help with the depression at 56 Hz, I removed the cut at 49 Hz.

The bulge around 35 Hz was explained by a boost there.  I removed that boost, and added a new boost at 20.7 Hz at as much as I dared (+5dB) even though higher measured better.

I added a new boost at 60 Hz to fix the depression on both sides of that.  As much as I dared (+5dB).

Each change resulted in better looking response.  Now it looks more like I am aiming for in the bass, relatively smooth from 250 Hz on down with a slight rise.

I saved the new settings in the left sub EQ to the Hotseat EQ.

New Left Hotseat sub EQ's

I worry mostly about the two new boosts.  The lower one might stimulate subsonics (which I can't measure with iPhone) too much.  I should sweep to be sure stuff doesn't go badly wrong.  But this new EQ looks good.

I wasn't going to make any adjustments today, but after I found the obvious one I just had to keep rolling.

Playing Bass Ecstasy by Bass Erotica and writing this up in the kitchen it was clear there was too much wall rattling.  I fixed that changing the bottom boost to 1/3 octave instead of 1/2, and then raised it to 22.4 for good measure.  That should also help keep tonearm resonances out also.

Two days later, I rolled back the 5dB boosts to 4dB boosts, reasoning that it makes very little difference in the response, and the lesser boost significantly improves dynamic range and lowers distortion.  The new response looks like this:

Left New Hotseat 11 04 26

Left New Hotseat EQ 11 04 26

A few hours later I'm thinking I'd like to both increase and retune the boost around 60 because the subs have plenty of dynamic range in that area and it's notably depressed at 56 Hz, though still much smoother than before.  I'd also like to fix the depression around 100 Hz, but I already eliminated the cut there and narrowed and raised the cut now at 112 Hz.  But it's way better than when I started, and that kind of fine tuning should probably include some oscillator sweeping.

Just after those minor changes, I decided to tackle the Right Sub EQ in a similar way.  It had a huge peak around 35 Hz (where there was a boost in the EQ) and a huge depression around 45 Hz (where there were two cuts in the EQ).

Right New Hotseat Before Changes

Removing the 35 Hz boost made it a lot smoother.  But even removing both cuts around 45 Hz failed to make that depression much better.  The subs have plenty of dynamic range around 45 Hz so I just added a +6dB boost right there, not entirely fixing the problem but helping a lot.

Right New Hotseat 35 Hz boost removed and 45 Hz boost added

Now the biggest problem seemed to be the depression at 125 Hz.  Removing the -2dB cut at 127 Hz hardly changed anything.  However I realized the crossover is around 125 Hz (or is it 120 Hz, I can never remember) and I wondered if changing the sub delay would help.  The subs were delayed about -1.6 ms from the panels.  I tried decreasing the delay and found a sweet spot around -0.6 ms.  With the LR crossover, both drivers should be in phase at the crossover frequency, so maximizing that point out to be the correct delay, so I stuck with that.  The distance seems to be somewhat greater than would be suggested by 0.6 ms, but possibly the EQs tend to mess up the delay a bit, so I'm sticking with the 0.6 ms for now.

It was still a bit depressed at 160 Hz, so I removed the sub cut at 152 Hz, making the overall response much smoother than before, so I decided to call it a day right there.  Way smoother than before, though I believe it could be made still better.

Right New Hotseat after > 125 Hz changes

Right New Hotseat EQ 11 4 26

Right New Hotseat Delay 11 4 26

Note that the delay for the panels is "standardized" at 10 ms, so a delay in the subs of 9.42 means 0.58 "less" delay.  Prior to this adjustment it was 8.42 and 1.58 ms "less" delay.

Things I need to do next include checking the sub balance.  I was going to do that but ran out of time and energy for the day.  The subs also need to be re-swept with an oscillator, and it would be good to do another sweep with both subs and panels.

I'm thinking the Right Sub level could be raised a few dB, raising the depression around 45 Hz

New Hotseat Position Measurements

 I'm calling this the "new Hotseat" because it's now a lowback chair (which makes for better imaging and measurements) and moved slightly farther back than before (because the speakers are now angled slightly more outwards than before, for better imaging in the back of the room).  

The panel EQ for the hotseat position is currently identical to the one now used in the back of the room (I haven't yet wired up separate EQ's for panel frequencies...which could be done but I haven't yet seen the need).  The EQ differs only for the "subs" where it is extremely important.  Flattening the bass at the center makes it way too strong in the back of the room, and flattening the bass at the back of the room makes it far too weak for the center of the room, generally speaking, so there need to be different bass EQ's--no question about it--if both positions are taken al all seriously.  The back of the room EQ also works pretty good in the sides of the room, where people watch movies so I call it the "Movie EQ"

The measurements don't look quite as good as when I did them two years ago.  (Note: these are just ad hoc measurements without a stand so far.  When I need to get really precise, to show the effects of small changes, I will start using a stand again, which takes considerably more effort.)

Left Channel New Hotseat

Right Channel New Hotseat

The left channel has a weird triangular shaped peak around 90 Hz where the right channel only has a modest "rise" (which in context looks more like depressions on both sides).  But (unlike the back) the lowest frequency bin (22.4 Hz) is not depressed compared to the midrange, only slightly depressed from the region around 40 Hz (where a huge modal peak is being suppressed by EQ).  Somewhat troubling is the rolloff above 1k which shows the -3dB engineered "Peterson Dip" (inspired by the Gundry/Linkwitz Dip) but only on top of much deeper lowpass shelf.  I think the lowpass shelf is largely resulting from being off axis from the speakers, which is hard to fix without messing up the imaging in the back of the room.  It doesn't sound as rolled off as it looks, there is a wonderful 3D image but only behind the speakers, sounding just slightly "distant" and never forward or aggressive as the Acoustats can sound on axis without EQ.

The original and still used Hotseat EQ has greatly increased bass compared with the Movie EQ, achieved through both higher "Gain Compensation" level and a few actual boosts (up to 6dB).  I don't clearly remember doing so, but I must have allowed for up to 6dB boosting by having a 6dB cut in the MiniDSP's which do the phase linear 8th order Linkwitz / Riley crossover.  It was absolutely necessary to do that in the high pass panel DSP because I could get +6dB ASRC* inter-sample-over peaks and clipping otherwise, but it not in principle necessary to do that in the lowpass bass DSP because low passed bass doesn't stimulate ASRC clipping. 

 (*Digital is not as simple as you think especially when there is Asynchronous Rate Conversion (ASRC).  I would have greatly preferred fully synchronous digital transmission in which the data is unchanged, but the miniDSPs don't have that option like my older Tact preamp.  But I've turned the defect into a feature by reducing the miniDSP digital input levels by 6dB which then permits up to 6dB boosts in the downstream DEQ's without risk of clipping.  Inter-sample-overs can occur when new datapoints are interpolated in between existing near-clipping high frequency datapoints....this almost never occurs in audio signals except with test signals designed to elicit the effect like those used in jitter tests--where there are often maximum level waves at the half the sampling rate.)

Hotseat EQ gain levels

Movie EQ gain levels

Hotseat Right EQ

Hotseat Left EQ

Not only am I using boosts in the Hotseat sub EQ's, I'm running the EQ at 0dB whereas I'm running the Movie EQ sub EQ at -9dB.  This is because generally speaking the back of the room needs a lot less bass.  However, that also means that I could boost the bass where needed up to 9dB or more in the movie EQ, which might be useful at the very lowest frequencies.  I'm already boosting the bass by up to 6dB in the Hotseat EQ, which makes it effectively up to 15dB higher.  Not knowing this, I had been shying away from using boosting in the Movie EQ even when I thought it might be helpful.

Spooky Good Imaging in hotseat position with lowback chair

For a couple of years now I've been optimizing the living room stereo for listening at at the center back of the room.  I created a new EQ for this called the "Movie EQ."  By necessity it had to be very different from the "Hotseat EQ" for listening closer to the speakers.  The Hotseat EQ sounds very boomy in the back of the room.  The periphery of the room magnifies the room modes, whereas the center position tend to cancel them out too much.

During this time I haven't bothered to sit at the old hotseat position.  I've loathed the idea of dragging my full back recliner back into the center position, especially since I try to show at least one movie a week.  I also feared all my optimizing for the back of the room had messed up the sound at the old hotseat, though I retained the original Hotseat EQ for the subs as a separate memory (which can be quickly loaded at pushbutton through my Insteon/Universal Devices home control system).  But I have no separate EQ for the midrange which has gone through a lot of changes too, and changes I made to the speaker angling cannot be easily reversed.

I bought a new lightweight low back folding chair for the hotseat position, but hadn't gotten around to trying it yet until the weekend just past.  I feared the hotseat position would be all messed up now.  But I started trying it on Saturday and then on Sunday found a truly wonderful position, about further 6 inches back from the original hotseat position with the recliner.  The new position is probably required because I changed the speaker angling to solidify the center image when listening in the back.  The speakers are less canted inwards, which is necessary to get a stable center image at all in the back of the room.

Listening to Citizen Steely Dan Disc 3, in this new hotseat position with a lowback chair, with the hotseat EQ selected, the imaging was Spooky Good.  It seemed like Donald Fagan and all the other musicians were right there in front of me. Nothing I've heard elsewhere for a long time has given me that same feeling.

The back of the room "Movie" listening position simply does not and cannot compare with this.  A much wider angle between the speakers is required, and there may be other advantages of being close up to the speakers.  There is much more direct sound from the speakers.  Some have described this as being like "Giant Electrostatic Headphones," even when both speakers are still in front.  (There are problems with trying to put both speakers exactly on the sides for stereo, though it can be interesting to play with.)

I do really need to use the hotseat position and EQ for serious listening, which I should do more often.

At the new hotseat, the speakers are about 45 degrees to my left and right on either side.  I'm about 5 feet from the plane of the speakers, and they are 5 feet apart.  But where to measure this is tricky.  If I measured from the middle of the speakers they would be over 6 feet apart, making the angle greater than 45 degrees.  But I now believe what is most important is the angle to the closest part of the active membrane, which is only about 2 inches inwards from the outer edge of the speaker towers.  That angle is somewhat less than, but still close to 45 degrees.  I would guess it is about 40 degrees.

I think the relative speaker position and angling is the number one most important thing in getting Spooky Good Imaging.

It was my friend Tim who originally told me, over 15 years ago, that I should experiment with sitting close to the speakers at a very wide angle, greater than the 30 degrees often suggested.  He was right.

He also said the exact position of the speakers and angling might not be the same for every person, because our outer ears are not the same.

If you keep the speakers at a fixed position, you move forwards along the center image to find the place where the center image disappears.  That means the angle is too wide and you are too close to the speakers.  So then you move backwards until the center image reappears.  Around where the center image reappears is the best possible position (or angle between the speakers).  Further back, and you get proportionally less direct sound, and the image becomes more diffuse.

That was essentially what I did on Saturday to find the new listening position.

Alternatively, if the listening position is fixed, you could move the speakers in and out from the wall, but for me and my speakers that would be exceedingly challenging for both physical and technical reasons.  I have the sub to panel delays dialed in precisely, for one thing, and changing the panel positions would mess that up.

Even if you ultimately end up moving the speakers, it's far easier to experiment by moving yourself closer and farther from them.

In the new position, the center is so perfect and well focused it's clear that my optimizing the speaker position, angling, and delays for the back has not messed them up for the hotseat.  If anything, it's far better than it was before now.

I purposefully did not angle the speakers outwards as much for the back as might have been beneficial there, hoping it would not mess them up for the hotseat, and my compromise for the back has indeed worked out perfectly for the front while being "good enough" for the back.

*****

I think having a lowback chair is good too.  When you are sitting in a high back chair, you get near reflections from the back of the chair in your ears.  These reflections matter more for imaging than for frequency response, but the frequency response is affected too, as I noticed when doing measurements.  I generally have always done my measurements with the chair in place because that is that is what you do when listening.

There's a long story here.  When I bought the current chair around 2008 I intended to take it to a furniture repair place and see if I could have the back shortened.  I knew this would be expensive but I figured it would be worth it.  I never got around to doing that.

The cheap folding chair I bought, which has flexible and ventilated plastic seat and back, is adequate but not as comfortable as I would like.  I think I will explore other options, like a director's style chair I already have, or others.

*****

The Citizen Steely Dan series became available in 1993.  While many people think of it as merely a repackaging of Steely Dan albums, it's a whole new mastering that was never heard before.  You knew about this if, like me, you read Steely Dan blogs around that time.  I also knew something like this was needed for a long time.  I don't know how it compares with later Steely Dan CD's, I suspect any high resolution versions were made like this too.

It turns out that one of my best friends was a techie hanger with Steely Dan.  He once invited me to the back room for a Steely Dan recording session.  I passed on this opportunity around 1976.  I had never heard of Steely Dan before.  Oops!

Later, I missed a chance to dub a copy of the master tape Steely Dan was circulating among its members.  I could not get there on time.  I ended up getting a second generation cassette tape dub (using my Nakamichi 600, and copying a tape another friend of mine had made on his Nakamichi 600) and it was a revelation.  A whole world of missing detail was on that tape that I never heard from the vinyl records.

(I think I can hear my friends voice on the master tape, and possibly on at least one song on Katy Lied.  You can also hear his girlfriend, who had originally been Denny Dias's girlfriend, playing some auxiliary percussion.  I could have been there too, dammit.)

For quite awhile I felt this was because tape is superior to vinyl.  But that wasn't the reason,  The reason was that the circulating master tape lacked the final Dolby processing and reverb that was added to the vinyl pressing (and also to early CD's).

There was a big technical problem here.  Steely Dan did all their recordings from at least Katy Lied onwards with dBX.  They needed dBX because of the incredible amount of overdubbing they did to make the final albums.  But the record companies only used Dolby A when making the final masters to be pressed on vinyl records.  So the final albums were retouched with EQ, reverb, and other tricks to sound OK and cover up the error in decoding.

In the Citizen Steely Dan recordings, they went back to the original masters, made with dBX, and decoded them with dBX the way they should have been.  Then they added the touch of reverb that may be less heavy handed than in the original vinyl.  The result is Steely Dan the way it should have been.  And it is incredible.  Even better than my second generation tape dubs, which have a lot of tape hiss (my friend and I chose not to use Dolby B at all).

This may be more relevant to some of the discs in the Citizen Steely Dan series than others, but it appears to be especially true for Citizen Steely Dan Disc 3.  I'm not sure if all the albums had the processing error.  I think it was true for the albums from Katy Lied to Aja.  I have never heard the songs on Disk 3 sound as good as they did last Sunday night.  It was Spooky.

*****

Among the changes I made when tuning my system for the back of the room listening position was changing the relative channel levels and delays.  I didn't know how this would work for the hotseat position, but I now know it worked out great for that too.

*****

I worked for 3 months on the subwoofer EQ for the hotseat position in 2024.  I ended up making giving it very smooth and nearly flat bass response.  Probably for many reasons, it is not as smooth now and could use a bit of rework for the new hotseat position.  But still, it is incredibly good.  It gives a somewhat higher bass level than I achieved for the Movie EQ in the back.

I wondered how this could be, given that the Hotseat EQ has many more and deeper cuts to eliminate room modes.  Well, there are two reasons.  The gain compensation for the sub Movie EQ has a -9dB setting for gain compensation.  For the Hotseat EQ this is 0dB.  I also added a 6dB boost for one frequency range in the Hotseat EQ.  Neither of these changes could simply be applied to the Movie EQ, but I might try doing similar things.

Laser Measure

 I read about audiophiles using laser measuring devices on Stereophile and even say they're essential for serious audiophiles (to get your speakers precisely positioned) I've never bought one.

This looks like one I'd like to get, a Mileseey S7.  

https://mileseeytools.com/products/outdoor-laser-measure-tool-mileseey-s7?currency=USD&sku=18063677008810900264450910&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&utm_source=google&utm_medium=PMAX&utm_campaign=S50&gad_source=1&gad_campaignid=23050170196&gbraid=0AAAAAoVRmp6WhX8rcXFFIy1Ypabp95nu0&gclid=CjwKCAjwqonVBhA4EiwA9wYJ3f5cErJTQ0TCJu2b96xTEdEz3BYFNRhfXWsYMBbCU4E1EmUYO8xjYxoC2y4QAvD_BwE

But since my income is limited, I plan to wait until I've sold surplus audio equipment of equal or greater value, which I really need to do right now for other reasons too but have been too busy with urgent household projects recently, mainly that I want to be prepared for the rain storms likely with the Super El Nino and have been working on critical hardscaping and drainage features all around the house, stuff I should have thought of 30 years ago before my house needed foundation repair, now I want to prevent it from needing even more foundation repair, fence repair, driveway repair, etc.

Polishing up the Bass

The two most recent posts revealed notable deficiencies in the bass response below 200 Hz.  The left channel has a minor depression around 90 Hz and the right channel has a minor depression around 50 Hz.  The former is more noticeable in the graphs.  However neither of these depressions coincides with a PEQ (programmable EQ) cut, so I can't fix either one simply by dialing back EQ.  And furthermore, nearby PEQ cuts were deliberately made quite narrow so as not to exacerbate them.  They are going to be tough to fix.

Probably the more audible issue anyway are the depressions in the range 120-180 Hz in both channels.  Those are entirely due to the panels, because the subs are nearly entirely cut off in those ranges (except just around 120) with very steep crossovers (phase linear 8th order pseudo Linkwitz Riley) that are already 6dB down at 120 Hz.  In the past I've sometimes boosted the sub response to fix such things, but I've decided it's best to keep the sub down below.  I'm already running the "subs" higher than most people at 120 Hz, but I can do that because my subs have output up to 300 Hz, very rigid cones, and I'm using 8th order filters on them (don't try that unless you also use phase linear Finite Element Response (FIR) filters like I do).  I cross over at 120 Hz because that way I avoid serious issues in both the subs (if crossed higher) and the panels (if crossed lower).  Notably the panels have fundamental resonances around 85 Hz which add distortion and can even cause the panels to rattle if driven too hard below 120 Hz.

The depressions around 160 Hz likely result from a combination of dipole bass cancellation and wall bounce.*  I already have the speakers 42 inches from the wall, and to put the wall bounce below the crossover point I'd need to move them at least another couple more feet from the wall, which is impossible in my multi-purpose living room where I also talk to guests and show movies on a projection screen.  Moving the speakers farther out the wall would also make it difficult to walk into the living room itself from the entry way.  Even a dedicated listening room would have the same problem unless I entered it only from the back, and I must also pass through the living room to get from the bedrooms and bathrooms to the kitchen.  The speakers are already as far out from the wall as I can manage with this house plan.

But it doesn't look like my old EQ settings are optimal any more.  I used a boost around 182 Hz in the left channel, and 133 Hz in the right channel.  And yet, in the measured response, the right channel has the depression which reaches from 140-180 Hz and the left channel has a very narrow depression right around 160 Hz.  It looks like I previously got these backwards, but also the work was done from the center room which may be different from the back, which the Movie EQ is intended to optimize, or there may have been other salient changes since I came up with the earlier boosts.

Even with these existing bass dips, the current Movie EQ settings are wonderful I think.  I watched the movie Contact (1997) on Sunday, which is full of deep bass, and the sound was full and beautiful, better than I recall hearing in theaters, and with no added "boom" as often happens in theaters.

I dislike adding boosts in my digital system because they can be headroom reducing.  Imagine you have a sine wave that sweeps from low to high very quickly (so as not to damage anything) at maximum level (0dB).  If you have a boosted range, it will digitally clip in the boosted range.  Now you would probably never want to run such a test, but if you happen to be listening at 0dB or nearby, as I often do for movies which have very low average level usually (to allow for big peaks) 0dB transients can sometimes occur in these ranges.

However, IIRC, I deliberately cut all panel inputs to the panel crossover device (a miniDSP-DRC with all digital I/O) by 6dB to prevent clipping due to asynchronous digital sampling.  I truly hate ASRC, it "resamples" a digital signal rather than just passing the data along unchanged, and therefore creates the possibility of digital clipping where there was none before.  I wish all digital were done fully synchronous as the Tact does it using 1999 digital chips, but hardly anyone does it that way anymore because they've all been scared by the "jitter" parade, meanwhile the importance of jitter is vastly overstated, and of no consequence at all for a device which is digital in and digital out.  I think there are still a few chips that support fully synchronous operation over SPDIF without a separate timing line--I use a separate timing line with my Lavry AD converter for truly perfect transfer--but it's simply not used much anymore otherwise--the miniDSP's don't let me select it because they don't have a separate timing line.  The Behringer 2496 DEQ's are also fully synchronous just like the Tact.  But sadly miniDSP decided to do things the "new" way, which introduces the possibility of digital clipping unless you are using their analog outputs.  To be absolutely safe from digital clipping, therefore, you have to reduce the level to the internal digital resampler by 6dB as I am doing.  This is no serious loss in the 24 bit or higher domain that the resample is working in.

Then I re-boost the signal 3dB in the DEQ's, which are fully synchronous.  That leaves me about 3dB headroom in the worst case.  I did things this way to allow for the 3dB boosts I was using before I started developing the Movie EQ, when I zeroed them all out for a fresh start.

So 3dB boost is all I can permit with my current setup.  In previous experience, that can be surprisingly useful, and you'd probably not want to use more than 3dB boost anyway even if you had the digital headroom for it.

I started with the Left channel and started boosting +3dB around 160 Hz with 1/6 octave.  But this created the condition where 160 Hz was higher than the 180 Hz band.  I pushed the PEQ frequency higher and higher, until at 170 Hz the two bands were equal, which also allowed me to broaden the PEQ to 1/3 octave without raising the already elevated band at 140 Hz, a pretty good compromise, and the "suggested EQ boost" fell exactly as much as with 1/6 octave centered at 160 Hz.   There's still a big visible dip, but the lowest point on the dip is not much more than other dips in the response above 200 Hz.  Also notice that the suggested EQ boost at 160 Hz has dropped from +7.6 dB (very bothersome) down to +5.2dB (meh). Don't aim for perfection, that usually ends up horrible, do what you can with limited EQ boosts like 3dB.   I've previously found such small improvements uniformly beneficial when larger or more complicated ones ones can get tiresome.  "Ship it."  

Also note that +/- response numbers vary enormously with filter bandwidth.  I could make this look nearly flat with octave bands, but's that nothing like music.   I use the minimum bandwidth and maximum fft size (which has huge effect on resolution) available to me to see the finest detail I can.  A sine wave generator or MLS generator would be better but requires much more complicated setup.

Left Channel before adjustment

Left Channel with boost at 170 Hz 1/3 octave

Duplicating this filter in the right channel wasn't any good.  It raised the respose at 180 Hz compared to 160 and 140.  140 happens to be already depressed, rather than peaking as it does in the other channel.  So I lowered the PEQ frequency to 160 Hz and broadened it 3/4 octave, which gives a fairly smooth U shaped response in the region centered at 160 Hz, probably the best that can be done with only one 3.0 dB boost, and the suggested EQ boost has dropped over 3dB (probably lucky sampling and less than that, it never falls as much as you have boosted and you're lucky if it's 0.5dB less...on a second measurement I got 4.8dB suggested which would be a 2.7dB drop from 7.5 suggested before adjustment but similar looking spectrum).

Right Channel before adjustment

Right Channel with boost at 160 Hz 3/4 octave

Right Channel with same boost later

Final PEQ settings for today 9-7-26 are

Left EQ 9-7-26

Right EQ 9-7-26

I played the entire album Bass Ecstasy by Bass Erotica at -1.4dB total (-1.3 being applied by Roon's album leveling) in the center back at it was captivating.  3D image, wall to wall, with impressively deep powerful tuneful and never unpleasant bass notes.  I remember when I could hardly listen to this at -10dB because of all the room boom.  I measured 93.1 dBC "fast" peaks on my SPL Pro app at the listening position.  dBC de-weights the deepest bass which will have peaks much above that measured flat.

The Movie EQ sounds great all around the house because of suppressing the primary house modes, and the way the Acoustats couple to entire space.  The Hotseat EQ exaggerates some house modes to get flat response at a close seating position.

Technical Notes

*The way dipole cancellation works is similar to a 6dB/octave lowpass filter that starts where the minimum width of the dipole is 1/4 wavelength and has cutoff (-3dB) where the minimum width is 1/2 wavelength and simply get worse all the way down from there. 

https://www.diyaudio.com/community/threads/dipole-phase-cancellation-in-esl-speakers.204246/

 The Acoustats are 20 inches wide so the rolloff begins around 170 Hz...just what we are seeing here, and goes down from there with the cutoff at 85 Hz and below.  However, the Acoustat diaphram is tuned so that it has a resonance around 85 Hz which cancels out the dipole cancellation from about 160 Hz down to around 40 Hz, giving the speaker a 40-50 Hz minimum response, at which point it is further assisted by room modes typically down to 20-30 Hz.  The diaphram gets looser with age so that the resonance goes lower and may not correct the response nearly all the way up to 160 Hz as designed, but instead extend further down, thus explaining the dip I see in that around 160 Hz, or perhaps it never does all that well around 160 Hz anyway.  Looser diaphrams from aging also explain why I get rattling if I drive the Acoustats too loudly below 120 Hz.  Brand new Acoustats would play louder in that region without rattling, but would ultimately reach their limits too.

Rear wall cancelation would be worst right up to the back wall (since the back of the dipole is out-of-polarity) and reverses to maximal addition where the distance to the rear wall and back is 180 degrees, then back to maximum subtraction where the distance to the rear wall and back is 360 degrees, with a neutral point in between.

maximal addition: 2D = wavelength / 2, then 2D = 3 * wavelength/2, ...

wavelength = 4D, 4/3 D

maximal subtraction 2D = wavelength, then 2D = 2 * wavelength, ...

wavelength = 2D, 1D

The average distance of the acoustats from the wall is about 3.5 feet or 42 inches.

maximal addition wavelength = 168 inches, 56 inches

maximal addition frequencies = 80 Hz, 241 Hz

maximal subtraction wavelength =  84 inches, 42 inches

maximal subtraction frequencies = 160 Hz, 321 Hz

More Imaging Improvements, need to get both level and delay correct

Previously I determined I needed about a 0.1 ms delay added to the right channel to bring the center image into the exact center position.  It's funny because the speakers look to be exactly equidistant, theoretically I could achieve the same result by moving the right speaker about 1.5 inches back, but it's already as far back as it can go because of the subwoofer and other equipment being in the way.  And it's strangely hard to dial in the correct position acoustically by moving the speakers which is very difficult to do especially considering how very important the angling is too.

It was also very hard to come up with the 0.1ms delay number itself, if I just play with the delay setting with the remote control I almost invariably came up with larger delays, which then were later found to introduce other issues.  The 0.1 ms delay is the minimum which causes the image center to move at all, and that's what the correct setting seems to be as it doesn't introduce other issues, and then somehow it seems right afterwards if not during the adjustment process itself where the ear keeps saying "more, more" until everything goes to hell.

The testing involved listening to mono'd sources and trying to get everything in the phantom center.

Getting the image exactly centered is surprisingly important in creating a holographic image.  Just a little bit off and and you have ping pong stereo with no depth.  Of course you cannot with multiple listeners siting side by side...that is one flaw in acoustical stereo.  You can get correct centering for multiple listeners only if they sit in front and back of each other, but that leads to other issues.

I don't like center channels either.  While that is the obvious solution if you MUST have multiple listeners side-by-side with at least some semblance of image centering for all, center channels always sound unnatural to me when I am at the sweet spot myself.  When you have a correctly centered phantom center, you have depth, width, and everything, with a center channel you just have left to middle to right, end of story.

But when I did this testing some weeks ago, and posted about it here, I did not at all try to equalize the loudness of the two channels, which has to be done with a different kinds of test.  Getting the loudness equal (and not influenced by delay) requires playing the same signal in one channel, then the other channel, and adjusting until they have the same loudness and general sound.

I did this playing pink noise only in one channel, then the other channel.  I'm shocked that there is no test CD with this kind of test.  I had to make one by taking a pink noise recording (from Stereophile Test Disc 2 IIRC) and then using Audacity to mute one channel or the other and making a new audio file from that.  Sadly I cannot distribute this test because it uses Stereophile's original "content."  I will someday have to regenerate it using the pink noise feature of Audacity itself, and that will also involve determining if that is as good as the pink noise from Stereophile, so I keep putting that off.

I suppose most audiophiles use an analog preamp with a balance control you can swing from far left to far right so they don't need such test signals.  But not only do most digital preamps lack such a feature, many purist preamps don't have balance controls either, and some that do don't allow you to swing from far left to far right.

The pink noise in each channel can be measured objectively with an SPL meter with "C" weighting.  You do not want to use the more well known "A" weighting, because that is for noise which is the stuff you don't want to hear.  The "C" weighting is for Content, the stuff you are trying to hear.  A flat contour gets it wrong too.  I use an SPL app on my iPhone to do the measurements nowadays, which gives me high accuracy and digital readout.  I use the slowest available response on my app, which is Slow and then do a mental averaging of the number.

I was shocked to find the right speaker was about 1 dB louder.  I wondered if it was because I'm using two vintages of Acoustat 2+2's on either channel.  But actually, I had previously attenuated the left speaker by 2.3 dB in the Levels menu of my Tact 2 Digital Preamp.  I had long forgotten about that.  I think I was trying to compensate for the delay difference by only using level adjustment, which is impossible.

I got the best result dialing back the attenuation to 1.0 dB.  Then the speakers measured the same loudness.  And when that was done, I also noticed the speakers sounded much more similar.

I then tried re-adjusting the delay in the left channel.  But the best image centering still seemed to occur with 0.1ms delay.  It seems like delay is the more powerful localization mechanism, so even if the levels don't quite match (within one dB anyway) the center image position is almost entirely controlled by the relative delay.

But getting the levels matched better than one dB, and with the correct delays too, it greatly improves the depth and realism of the image, I determined in subsequent listening.

Current settings:

Delay: 0.00 ms Left, 0.10 ms Right

Level: -1.0dB Left, 0dB Right

This was in center back seating position of the room, I think it should work in the closer up position too.  Sometime in the past few months I had eliminated ALL EQ's from the Acoustat feed because I figured they were not well optimized for the back of the room (and maybe not for the more frontal listening position either).

The overall response seems fairly flat until you get to midbass frequencies 200 kHz and below where there are some dips, those are problematic to adjust because I'd need to add "boost" which I try to avoid as it is headroom lowering.  The subwoofer feed has several EQ's to deal with room modes, but the subs are cut off with a steep FIR linear filter above 120 Hz  (FIR linear filters are digital magic which introduce no phase shift) so the subs can't help with dips above 120 Hz caused by back of room reflection and dipole bass loss.

Though I've done this in the past, I generally do not like leaking some sub base above 120 Hz to "help" the panels.

The left and right channels measure about the same from 300 Hz on up.  They sounded very different before the level adjustment, after the level adjustment they still sound a bit different.

I need to dial in EQ's better AND measure and adjust bass and panels separately, and then go back and check levels again.

After any kind of EQ adjustment where channels are equalized differently, you need to re-measure channel loudness as I just did, using single channel pink noise and a C weighted SPL meter, and not rely on image centering which is more controlled by delay when the channel levels are already fairly close.