Saturday, July 22, 2017

R2R Magic!

I've been struggling with trying to make Hot House (Arturo Sandoval) sound listenable.

I've been adjusting EQ.  I balanced the two supertweeter channels, connecting the DAC directly to the Parasound Power amp, not using the Harrison Labs -6dB attenuator (which isn't perfect and increases load to 2k) and instead using the Parasound attenuators.

None of that seemed to cure the problem.  But one more change seems to have magically changed everything, not expected at all, and it's all probably bias and measurement error.  But sure enough swapping my second Denon DVD-5000 for the Emotiva Stealth DC-1, and readjusting the digital gain a bit since the DVD-5000 doesn't have gain control like the Emotiva (which I had set to -6dB after removing the attenuators).

I had to do a lot of rethinking the digital delays, since now for the first time both panels and supertweeters are on the same kind of DAC, and that wasn't true when I did the Tact setup.

Now, strangely, I have pretty flat response to 20kHz.  The added steelyness is gone.

And yet, there isn't really any audible output from the super tweeters any more, or very much.  I can measure the 18-20k they are putting out, pretty much as before.  But now I hear nothing.

Some strange force leakse out of sigma delta dacs, ,a force below the actual audio signal they carry, a kind of low frequency force which makes other sound waves vary their phase, making things sound bad, even though it's not a measureable sound as such, just a magic force field that affects other sounds.  The feedback of the sigma delta is "correcting" everything else in the room in an undesireable way.

Or maybe the story is just that I should always be using the same kind of dac for super tweeters and panels.  That might not seem like a bad idea for a lot of reasons.  And possibly the bass too.

In fact I made this change not expecting it to make any difference, but after testing the new DVD-5000 to be the same as the other (excellent, the best of the Dual Differential 1704 Dacs I have measured)  I thought it would make things more convenient because now I don't really need to bother readjusting the midrange delay for 44.1k vst 96k or whatever, since they are now the both kind of dac.  I don't know the sub delay even as close as the 0.44msec difference, so it hardly matters to the bass.  But maybe having another DVD-5000 for the bass would be the final magic touch (and it just seems so much like my kind of all antiques system).

Maybe in that case whatever the drift it, it stays the same, rather than constantly going out of phase with each other or something, even while the average delay has been compensated for.  There is still the matter of the supertweeter delay because of physical distance, and I've tried to re-figure that, but maybe needs redetermination using something better than the Tact program (which is very weird, btw, I think it uses an essentially analog stimulus and shows you the uncorrected response of that stimulus rather than a corrected impulse, which many programs show).  But even though changing that seems to make a slight difference, it's not like the vast improvement that has occurred.

But I'm not sure it entirely matters either, as the long length of the acoustats mean there are different possible delays for every position, and if most sound you hear is reflected, the average matters almost as much as the direct path distance.

Update: Maybe true, maybe not.  Further testing confirmed what was suggested by earlier Tact impulse responses.  There is a 14kHz resonance in the left Elac tweeter, from an earlier accident.  The other channel does not seem affected.  To fix it for now, I have replaced the left supertweeter with a Dynaudio D21, mounted in a modified LS 3/5A cabinet, with the tweeter wired in directly.

The result looks a little crooked, since for now I've left the right Elac on the right side.  I'll have to come up with a more elegant replacement for the left side also, but for now the combination seems to work fine and has been level adjusted.  There's a 0.5 uF cap on the D21 to attenuate the fairly noisy power supply of the old HCA-1000A.  The Elacs have long had such attenuation with their own crossover, which I think works at about 12k, which I have largely ignored since I cross over much steeply.

Oh, yes I'm now crossing over 48dB quasi Linkwitz-Riley with 4 series "HC" filters each 12dB/octave, and at 20kHz.  Need to get all that super tweeter stuff out of the lower audioband.

High frequency response up to 20kHz is flattest ever, for some reason the system just got a lot flatter recently, I still don't understand why, about the same time as I replaced the DAC on the supertweeters with the Denon DVD-5000, but with or without the supertweeters running.  And no notch filter at 12-14kHz is needed, the strange ringing there is mostly if not entirely gone, playing music I see all the bands from "flowing" naturally with the program, the very top 20kHz being slightly depressed, but I don't want to crank up the gain any more (already at +4 for the super tweeter, less the dialed in attenuation in the back of the Parasound amp, which I've readjusted for the same effective 20kHz output at the listening position.

No comments:

Post a Comment