THE PROBLEM
Nowadays I mostly use the "Movie EQ," which optimizes the back of the room listening position. It definitely works best for background music anywhere in the house. The "Hotseat EQ" only works good at the "Hotseat" a few feet from the speakers, where I do really really serious listening. But I've hardly had any time for that recently, and it also requires dragging the listening chair into the Hotseat position and putting it back afterwards, which I'm generally too lazy to do. I've been keeping the living room ready to show a movie on short notice, and I've typically been watching one movie per week with friends. And most of the listening I do is background music listening anyway, for which the Movie EQ works best.
Back when I last fixed the Movie EQ in September 2025, I simply removed the midrange EQ's from 200-1000 Hz which had been worked up for the Hotseat EQ in 2024. At the back of room position, they did more harm than good. I didn't really have time to cook up a new Movie EQ for the midrange, as I had done for the Hotseat EQ a few years before. I left unchanged the upper frequency EQ's, whose basis was mostly subjective (objectively they caused some rolloff above 2k, which I rationalized as the "extended Gundry/Linkwitz dip" needed for large dipolar panel radiators like my Acoustat 2+2's). The resulting response looked flat enough and it sounded great in the back of the room. I felt it was nearly as good as the Hotseat EQ is at the Hotseat position, but without all the fiddly midrange adjustments. Anti-EQ fans would naturally think it better with less EQ also.
But there was a very annoying flaw in the ointment. If I adjusted the two channels so they were at the same measured SPL level on pink noise, AND the same subjective loudness when played one speaker at a time, the center of a stereo image often seemed to be on the right side, just about at the position of the right Acoustat speaker! Often lead performers who I knew had to be in the center was coming from the right. That kind of thing bugs the crap out of me.
I just had to correct that somehow. The quick fix I came up with then was to attenuate the right channel by a whopping 3.4dB in the Tact digital preamp. To this day, now 4 months later, I have found no better way to center the stereo image at the movie seating position. No other change so far seems to help enough, and when I go back to a test of some kind to re-set the "balance" I still end up having to attenuate the right side by 2-4dB.
(Also no other device in my chain lets me control the relative channel levels, something I find very annoying as I think all the digital processors I have should do that, especially the Behringer 2496's which could have different relative level settings for different EQ's, which often makes sense.
(NB: It seems I have rarely paid any attention to the LEVEL controls in the Tact that can be used to set the L-R balance. I didn't take a single picture of the Tact settings in September 2024 when I did a big system re-tune for the hotseat. I think I have long attenuated the right channel by something like at least 2dB without paying any attention to it. So, the "off balance" thing is not new, I'm just paying more attention to it, and I think it has gotten worse in the Movie EQ scenario than it was before.)
Even that 3.4dB right attenuation is a conservative estimate. If I just play with the right attenuator using my remote control, and go back and forth until I get the most centered image with a mono signal, I typically end up with something more like 6.5dB. I'm horrified by having it set that high, so I then back off until just before the image solidly flips to the right again. And that point is about 3.4dB. If I want to dial it in so that it starts seeming to come from the left, it takes a whopping 9dB attenuation on the right side.
Early Thoughts
Likely Room Acoustics, but how?
Right now I strongly suspect that room acoustics is weirdly involved in this, including the kitchen doorway a few feet to my right (I think that allows energy to leave the room from the left speaker which is more aimed to it, whereas the corner on the left amplifies the right more. But any explanation involving "amplification" by room acoustics has to contend with the issue of why when the channels are set to the same level, with 0dB of attenuation for both, the channels sound equally loud when played by themselves*, and there is no weakness at all on the left side, and at -3.4 dB the right yet by itself sounds clearly muted compared with the left. And yet, with the two channels sounding obviously different in level, that attenuation is required to get a solid centered center image.
(*To listen to each channel by itself is hard in my system, and I put that obvious test off until recently. I have no buttons to do this kind of test easily, I can't even just disconnect a speaker wire because there are also the subs. I have to run down the attenuator on the Tact digital preamp for one channel in the LEVEL menu to -99.9 dB, which takes quite awhile, and worse is that I have to try to remember what the attenuator was previously set to, which I nearly always forget to do, or don't bother to write it down. Doing so requires crouching down, I now avoid getting on my knees, and remembering which button is the menu button. So doing this requires a lot of time and steps. It would sure be nice to have Left-only and Right-only buttons. But I don't see such a thing, only in rare cases (like the Marantz 2270) buttons that will play the left or right input from one channel to two channels, which is not at all what I want.)
I think perhaps the greater room amplification of the right side could mean that if the room modified levels are the same, the direct response is actually lower on the right. Putting my ear up to the speaker, however, there appears to be no weakness on the left side either, it seems clearly louder than the right side when the right side is attenuated by 3.4dB. So why oh why must it be louder so I can get a centered image?
Frequency Response Differences
Dynamic and Non-Linear effects
And there could even be, I am thinking now, certain non-linear effects. The right side might have dynamic loudness increases due to distortions of some kind, such as could be introduced by failing electrolytic capacitors or transformers in the speaker interface. Counterintuitively, distortion can make things sound louder because harmonics are being added.
I hardly want to get into the differences between the two speakers. I generally think of them as quite minor. They both feature the final Acoustat 2+2 "C Mod" modified interface, one side has a stock interface originally made that way (in the small Hafler designed box) and the other has an interface modified to be C Mod by a famous Acoustat restorer/upgrader. So they're both C Mod, which is the most important thing, that affects the frequency response, the loading, and many other factors. Now the factory C Mod box also has the Medallion transformers, and the other side does not, but those transformers were not said to affect the static performance, including the loading, frequency response, anything like that, only the higher output capability from freedom from overloading. So in just that way, as an example, dynamic response could be a factor. But the improvement wrought by the Medallion Transformers is said to be only at the highest listening levels, and I'm no where near those, so I discount the possibility that this is the issue, but it could be. Also the C Mod itself reduces the transformer overloading issue too, further making the possibility that this is the issue unlikely.
Investigations
Mono Mode
Adjusting the EQ
So I then though I should use some kind of banded stimulation test. I used to hand sweep 1/3 octave pink noise, but I haven't used the equipment I used for that purpose in a very long time. What's more commonly available now is warble tones, Stereophile Test Disk 3 has a nice set for the Bass Decade, Midrange Decade, and High Decade.
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| Left Channel "Movie EQ" September 2025 |
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| Right Channel "Movie EQ" September 2025 |
Since it seemed the image pulled to the right, the obvious thing to do seemed to be to be to reduce the sizes of the HF cuts on the right. I did so by a few dB on each cut. That seemed to help on the warble tones themselves.
Still, it seemed I couldn't quite balance the tones at 9kHz and above. I cranked up the HF control all the way to maximum. That seemed to balance the highest tones.
It was only then that I decided to listen to the speakers themselves. With the new adjustments, the left side sounded loud and bright, the right side sounded way softer and heavily rolled off.
I then tried reducing the cuts on the right side. I cannot easily change the attenuator on the right side, so I didn't do that. That made the right sound more like the left when played by itself.
Now thinking the right to be slightly bright, and unbalanced there, I reduced the HF attenuator back to the midway position it had been at before. I was totally mistaken in thinking the right side needed boosting, or less cut, because it was wearing out or something.
And even with modified boosts, blindly setting the balance by adjusting the left attenuation still seemed to end up around 3dB.
Speaker Angle and Position
I started to notice the angle of the right speaker was just a tad more on axis. With the Acoustats, you generally never want to be exactly "on-axis." That was certainly true with the 1+1's, maybe less so (or not?) with the 2+2's. You want to be off the axis of the speaker. Acoustat specifically recommended listening off axis by some amount up to you.
Many people do this by having the speakers parallel to the wall behind them. I prefer to call this "Zero Toe In," though some people define the toeing relative to the listener rather than the rear wall, which might not be a straight wall. My friend George was a true believer in the Zero Toe In principle as I'm defining it (and he called it that too) and that anything else was infidelity. That was one of his most foundational rules, going back to the early 1980's if not before, so he hardly ever talked about it, except when visiting anyone who did otherwise.
I've never seen any particular reason for Zero Toe In, but if you do it of course you will be off axis from the speaker, by some amount varying as to how far you are sitting back. And there's the rub. You might need to get very far back for the Zero Toe In to be correct relative to you. An easy solution is to toe in the speakers by some amount, but never by enough to put them on axis with you, the listener, at the hot seat position. That way you have more freedom to determine how far back your are going to listen, and therein is an even longer story.
I ended up choosing both the serious listening position AND the toe-in following the advice of another friend, Tim. Tim emphasized getting as wide a stereo angle as possible, but just short of being too wide for the stereo image to collapse. Unless you have a very wide room, and I have a rather narrow room after you account for bookcases and furniture, this means sitting rather close to the speakers. This gives me about 45 degree angle to the center of each speaker. If I go in closer to the speakers, the stereo image begins to "collapse" (actually, it begins to lose a center, everything seems to be coming from everywhere, so perhaps it would be better to say it "explodes").
Once you have that chosen, you angle a pair of electrostats outward from being on the listener axis, just before the highs begin to really roll off, Tim advised. The point was also to enable as much stereo separation as possible. The more off-the-listening-axis the speaker is, the more it's going to stimulate the ear on the other side of the head even less.
Tim's advice gives me astonishing realism, when I'm willing to bother to move the listening chair into the exact correct position.
From the more semi-casual listening position in the back of the room, the speakers might be better aimed more off-the-listening-axis, which is to say less toed in. George's zero toe-in strategy might even be correct...for the back of the room.
Here the stereo angle has also already been reduced from around 45 degrees to more like 22 degrees, so there is far less stereo spread. You might think this would make the center "tigher" but actually it has the effect of making everything "looser," probably especially because of room acoustics.
But I'd really rather not have a special toe in for each listening position. I'd rather leave speaker toeing at what's best for the 'serious' position in front, and try to cope with that somehow in the back. The back is never going to have the astonishing stereo spread of the front.
I did correct the angle of the right speaker, so it's slightly less on-axis, and matching the right side, and that did seem to improve things, but not enough to change the right channel attenuation needed more than a fraction of a dB.
I tried pushing the right speaker back by a very tiny amount (there is not much space and they are incredibly hard to move now that they've sunken down into the carpet for a few years...and they have built-in cork feet). But counterintuitively, that only seemed to make the image center even more to the left, so I quickly tired of that kind of adjustment. That and I'm strongly inclined to believe the timing is near perfect to begin with, so I actually haven't experimented with that yet, and it would also be something to consider.
It's hard to measure the exact speaker to wall distances, because there are different things on the wall in either case, such as the window on the right side. But with the angle corrected now, the two speakers measure the same to the closest inch if not half inch, comparing both speakers on the inside and on the outside.
