The White and Black 2+2's

My blog photo now represents the new living room system reality.

I'm using one white Acoustat 2+2 from my original pair of 2+2's that I bought in 2019.

It's mate had an issue I was long aware of, but mostly thought I'd solved.  I don't believe I had.

On some recordings, there was a terrible resonance with some combination of bass frequencies.  I first heard it on the Grouse album 'We Want to be Loved' with the track 'Suicide kills me'.

I pretty much eliminated the issue with my 125 Hz 8th order crossover, which also resolved what seemed to be other issues resulting from rear-reflection and Acoustat resonances.

When testing the new black 2+2 I just bought in December 2023 before purchase, I noticed a similar issue with 'You Know Too Much About Flying Saucers' on Hello Waveforms by William Orbit, on one of the new speakers.

Well that same new speaker had a continuous but almost inaudible arcing problem I could only hear with my ear right up to the speaker.  I could not smell anything and believed the ozone emanation was trivial, not unlike with a small motor perhaps.  So I figured it was fine in the well ventilated but rarely used living room, but perhaps not so fine in the bedroom.

But rapid ABX switching of the speakers, and/or leaving the speakers connected to the running amp while plugging it in, or some other experimental mistake, I blew out my Hafler 9300 in one channel.

I don't really know that the arcing speaker was at fault.  Perhaps the ABX switching itself is unsafe (but it never hurt the Hafler or Aragon before, only the Krell).  But the coincidence of having an amp fail within a month after connecting to this arcing speaker makes me wonder.

(Also, the guy I bought it from, I well knew was having endless weird problems related to the 2+2's if not other things.)

Now perhaps the problem only occurs when the speaker was being charged up (though once again, that was never a problem before).  I'm resolved now to plug and unplug acoustats from AC power ONLY WITH THE SPEAKER LEADS DISCONNECTED.  You want the HV to stabilize before connecting an amp to it, especially if there is an occasional shorting issue.

But that kind of thing can't be prevented, for example, if there is a temporary power failure, when the power is restored once again the interfaces with be charging, mostly likely with the speaker leads connected.

So, I consider the second black 2+2 with arcing to be unsuitable for use except with "expendable" amplifiers.  Perhaps things like one of my two HCA-1000A's.  Not that special.  AND MOST CERTAINLY NOT WITH MY ARAGON 8008 BB !!!  WHICH HAS UNOBTANIUM TRANSISTORS!

And then I decided also that on complex music, the arcing 2+2, even if the arcing wasn't audible, still made for it sounding fatiguing after awhile, which I determined might well be traced to the arcing causing unstable membrane voltage.

Now the faulty black 2+2 has been moved off to my bedroom so it can be easily accessed for repairs.  I've decided it's the first 2+2 I want to fix, though it might be harder to fix.  I want to end up with two of the black ones, because I think they are better somehow, tighter membranes perhaps.  They were much later production, most likely made in Arizona instead of Florida, though not as far as I can tell using the later improved coating.  Perhaps other construction details had been improved.  Or perhaps they were just less used.

I can now mostly rule out the issue being a difference in interfaces, because I have been using one of my old Red Medallion interfaces with the new 2+2's, and my white 2+2's had a C mod done on them by a well regarded Acoustat refurbisher.

But it is true, though I often forget and doubt it means much, that the white 2+2 I am still using still has the non-Medallion transformers.  I plan to swap it with the other large-interface I have which has the a recently made Medallion transformer I installed in my first attempt to repair it, before I noticed that the issue was that the 'crossover' board had been connected incorrectly.  I then didn't bother to take out the Medallion transformer, I figured it was better anyway, even though there was now a mismatch with Medallion HF on one side and not the other, which I could never tell that any difference resulted from that.

THEN, I will have Medallion HF on both sides.  There will still be a lack of Medallion LF on one side, but that is said to be even less important for the sound.  It seems one of the primary purposes of the Medallion upgrade was to prevent transformer failure with improved insulation.  It may have also resulted in tighter coupling, and the improved sound was hyped, but never taken by anyone as a kind of 'night and day' difference, the old non-Medallion transformers sounded great too, and just doing the "C" mod alone is supposed to make a far bigger sonic difference than the Medallion transformers, though they're great if you got 'em.

Anyway, even right now there's still a difference between my good white and black 2+2's, despite both having "C" mod, and probably not just because one has Medallion's and the other not.

Now in these response I'm going to show, ignore the bass below 125 Hz, that's may look bad because of the new 'background' EQ that was operating in the bass, which produces a suckout around 45 Hz at the listening position.

(Update, I've discovered an error in the sub 1kHz eq, the left and right don't match in the GEQ section, it looks as if I've simply failed to dial in the Right channel, which is possible, back after my chairside EQ died.  It's unlikely the two channels previously needed lots of eq in the left channel and none in the right, in fact the right white speaker, now removed, was very problematic wrt EQ.  That explains some of the weirdness below 800 Hz in the right channel.)

I've always turned the HF level on the white acoustats to about 12 o clock, when I now understand 'flat' is supposed to be 3 oclock.  So what would 12 o'clock be?  I'd guess around -2.  I previously thought 12 o'clock sounded best and was supposed to be flattest.  (I'm applying a vast amount of HF downwards EQ above 2kHz too, without that and the HF adjustment it would be about flat to 17kHz.)  I have a smallish room which probably requires downward HF EQ.  It's not a particularly lively room, just about balanced perfectly for conversation.

To match it I've dialed the interface on the black units down to the lowest HF level the compact interface permits.  It's a very limited range of the 16 ohm resistor.  I'm guessing that level is around 2dB also.  And lo with these settings the frequencies 10kHz and above are fairly well matched.)

Also note that EQ from before IS being applied, as well as the 8th-order phase corrected crossover at 17kHz for my supertweeters when I no longer have supertweeters, but I haven't gotten around to taking it out and think it might improve the sound anyway because of the phase correction.

That EQ was dialed in by ear with the original white 2+2's, which seemed to need a 3dB (!) boost at 1kHz to sound good, also at 850 Hz at 3dB.  Otherwise, the midrange sounded weak, perhaps not just with regards to it's immediate surroundings.  Prior to EQ 2kHz measured higher than 1kHz, even with 2kHz dialed down.

Well, it seems the 1kHz boost is simply not needed with the good black 2+2.

Taking that out, or even just cutting it back to 1dB was sufficient to fix the 'balance' problem I had fixed by ear the day before by cutting the left channel 2dB in my Tact.  (But if I dialed it back to 0dB, I'd then need to cut the right side to get it to balance, so I'm now using 1dB boost at 1kHz for the black 2+2, pending further investigations.)

Now, it would be hard to believe that the Acoustats were originally voiced with a 3dB suckout at 1kHz.  I think that correction may have been needed because of membrane aging on the white 2+2's.

The result is that images are nicely behind the speakers as they should be, much clearer images than I've ever had before thanks to the speaker swap, removing the supertweeter towers, and possibly other recent changes.

Anyway, prior to adjusting the 1kHz EQ down in the right channel, here is how the white and black speakers now on the left and right sides respectively measured:

Left Channel with White 2+2

Right Channel with Black 2+2

You might notice as I just did that the actual level of the 1kHz bulge in the right channel doesn't actually reach quite as high as the narrower bulge in the right channel.  True, but the above measurements are WITH a -2dB reduction in the right channel level, as I needed to achieve left to right balance.

Don't pay much attention to irregularities above 2kHz as the measurement device is only being held in approximately the same position each time.

After taming the midrange bulge by tamping down the +3dB EQ at 1kHz to +0dB, it's looking a little different:

Black 2+2 with 0dB boost at 1kHz

But now 1kHz is lower than 800kHz, so I decided to up 1kHz to +1dB and cut the +3dB boost at 800Hz to 1.5dB, resulting in this:

Black 2+2 with less EQ at both 800 and 1000 Hz

That's the best yet in terms of flatness through the 700-1500 Hz range, and with these changes it no longer needs a -2dB overall level reduction in this channel.  Apparently the image shift was caused just by the boosted midrange.

However, noting that there's still a measured boost in the left channel, I'm wondering whether THAT is correct too.  But exploring that will require subjective testing, the way I arrived at the need for a boost there in the first place.

Sound level measurements with RTA are never definitive, only a guide to what's probably right.

But it occurs to me now that perhaps I boosted the midrange mostly because of issues with the right channel white 2+2 that has now been replaced.  It might have had quite a suckout in the midrange which I was compensating for by boosting both channels.

Meanwhile, I should also address the sub 1000 Hz issues that are apparent in these graphs.