Monday, November 14, 2011

Coherent Imaging and making the speakers disappear

More than two months ago I moved my supertweeters out of the living room.  They were contributing to a gridlock which made it impossible to move the Acoustats.  Since I am now (since early this year) listening from a position much closer to the Acoustats, it was seeming like they might be too far apart for the close-up listening position.  The angle between the speakers from my head was more than 60 degrees, and while I was still getting a center image, beyond the center things seems a bit vague,

Finally on Sunday evening I started moving the Acoustats laterally in toward the center.  First about 5 inches in on either side, then a few more inches which reached the maximum point I could move them inward because of my electronic equipment.

The new position also allowed me to move the listening chair even closer in and still get a stable center image, and moving closer in gave me nicer bass.  The nicer bass is because I am closer to both the Acoustats and the subwoofers, and because I'm moving away from the center of the room where all room modes have their main cancellation and there is a big bass suckout.

But there were two problems now.  The image started to get a shrunken quality, with the soundstage no longer seeming life sized.  And now, some instruments seemed to be playing right from the speakers themselves.

To fix those problems, I moved the Acoustats slightly back and slightly to the side.  Because of electronic equipment, notably the tuner and the MSB PAD-1 which converts the tuner output to digital, I couldn't move the speakers back more than about 4 inches.

But that 4 inches made a magic difference.  Now the speakers themselves were not longer clearly the source of as many instruments as before.  Instead, the position of those instruments moved forward, to the the same depth as the center of the image.  Thus the center of the image was no longer by itself, there is now a right-center and left-center, and much of the music appears to be coming from a plane about 3-10 feet back from the speakers.

So I'm glad I started these speaker moving experiments because I now think I may have some of the best imaging I've ever heard.  I plan to move some of the equipment so I can move the speakers even farther back from the listening chair, and possibly more the the side as well, for an even better, more lifesized image.

One thing very peculiar was that I need to dial in about 0.23ms of right channel delay to make the center image work.  Either that, or move physically closer to the left channel, so that it seems I am way off center.  I dial in this overall delay very conveniently using the Tact, though it can't be correct that way as it affects both subwoofers and speakers alike.  I tried muting the subwoofers, and I still needed that 0.23ms of delay.  Notably when I muted the subs, I also noticed that the notes in the bass line for Spanish Harlem began to sound equal, though at a much lower level.  That's very strange also because when I muted the subwoofers I have very little bass response below 85Hz where the subwoofer crossover is, and that is basically where all the first 3 bass fundamentals are.

The need for delay is very puzzling.  It might represent some early reflection, or some difference between the speakers, such as the fact that I replaced the 40 uF cap on the right side with a nice 630V solen film capacitor, but haven't made that same change to the left side.

***** Update

The next day, the need for a 0.23msec right channel delay disappeared.  I was listening to a Cactus Pear recording in which violin sounded slightly to the left, and piano more toward center.  I was thinking at first this was a demonstration of the wider center image (including left center and right center) I bragged about yesterday, but to be sure I tried headphones and realized violin (played by Stephanie) was supposed to be in the center.  Dialing back the delay to zero fixed the problem.  I recalled some of the songs I had listened to on Sunday night, and there too the need for right channel delay disappeared.

I have to believe this was either a temporary threshold shift or some similar problem with my own hearing.  It's true I was listening fairly loudly, I noticed I had heated up the Aragon amp to 150 degrees F.  But I noticed the need for delay before cranking up the volume.  Maybe it had to do with my cold, or a temporary earwax configuration.

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