Monday, May 26, 2014

Sounding Good Now…System 5

I've decided to give the current living room system a special designation: System 5.  This counts back various ways I did the living room system since I got the Acoustats.  A friend agreed the system was sounding better than ever.

The current system 5 includes special DAC for the Acoustats, currently the Onkyo RDV-1.  For what it's worth.  I suspect the PCM 1704 used BB's DF 1704 for digital filtering.  DF 1704 is an 8x oversampling unit.  The combination of 1704 and 8x oversampling was also used by the Chime DAC, which friend Tim says is the best ever DAC he's heard.

One of my subs has the Sledge Amplifier, which may sound more tuneful than the BASH.

I've re-tuned the bass EQ, not entirely eliminating boom around the perimeter, but letting enough through so bass tunes are not lost, and have a bit of weight and authority.  This is judgement call, but basically -8dB at 45 Hz instead of -11dB.  Plus the bass level is raised 1-2dB from before.  I dialed back in 4dB of 30Hz boost eq on one side and 2dB for the hallway sub (which seems to have large excursions…and dialing back 30Hz eq to only 2db helped).  The idea of 30Hz is that it adds about 2dB weight to 32 Hz, but also gives boost to the 20's, which aren't overdone here (they show up as very weak strangely on Android app).  The Q is 1.3 to 1.6, not sharp.  The corner sub also gets 1dB of boost at 20Hz.

Basically, the Bass is boosted slightly compared with System 4, which was max cancellation of boom.  But often turned off by mistake, because max cancellation was not very satisfying.  I'm also using LR24 vs LR48 crossover by necessity, since that's all I can create using DEQ for crossover which lets me use external DAC.  But the use of external DAC has one thing I keep forgetting to mention, perhaps because it reveals a weakness of previous DCX systems I didn't want to mention, perhaps.

The problem is that the high max output of the Behringer DCX 2496, 10V,  means that you waste an extra 10dB of digital resolution into home audio components.  This may not be a huge problem, looked at the standpoint of the 24 bit DAC's having more resolution that you might ever need: 144dB.  But of course they don't provide quite that much actual dynamic range, or S/N, or things like that.  Say if the converters have 120dB dynamic range, using them at -10dB and below means you effectively have only 110dB.  And so on.  So this is an important consideration.  The max digital level should correspond to a max output that you never get to, but come fairly close to.

Many people who hook the Behringer up differently complain about the noise, or whatever, resulting from the high max output.  But using digital inputs, I was not getting noticeable noise, running straight into my midrange amplifier, the Aragon 8008 BB driving the Acoustats.  The problem, if there was a problem, was not so obvious as hiss.  It was sound with less there there than there should have been.

Many people have solutions like external attenuators (which I use on the bass, but determined did not sound good on miss or highs).*  (The DCX outputs get increasing distortion above 2V output.  They are excellent 2V and below.  But near 10V distortion rises to near 0.1%.  That's what you see when you use an external attenuator.)  Or transformer outputs (I eschew ferromagnetism in the signal path).  Or a re-done output stage…YES that's what this unit needs.  I would say the max output should be set to 4V.  2V doesn't push a lot of amps to their maximum.  And the 4V output should be clean.  0dB digital should correspond to 4V output.

With my system 5, I'm getting about 2V max output in the midrange at 0dB digital.  This seems to play about as loud as I actually need, though it scares me that I might run out of digital headroom.  Anyway, I'm not wasting 10dB of dynamic range as I was before.  And that could be as big a difference as having an R2R DAC.  Or not, or both might be unimportant.

Anyway, the overall effect is a far more musical system than ever before.

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