In past 2 days I wired up, programmed, tested, and listened to the new miniDSP OpenDRC 2x2 boxes.
Using a new 4 AC outlet Powerbox from Cullen Cable (nice, all metal and heavy, with real industrial grade outlets, teflon coated twisted conductors in a shielded cable), which I waited for since March when I ordered it, arriving last week. That is where the 3 minidsp power adapters plug in. Rather than trying to rearrange everything in front of speakers to make room for one new powerbox, I simply placed the powerbox on the huge Panamax 1500 power conditiioning UPS that everything else, except amplifiers, connects to through 5 now 6 sub-strips like this Powerbox. I had previously been using another of these Cullen Powerboxes for the Behringer DEQ's, the Tact DSP preamp, and the ABX switch. I decided these big heavy metal power boxes are good for powering digital devices.
The "plugin" software from minidsp is poorly documented and quirky, but works, and thanks to reading blogs at miniDSP (which is in Hong Kong, btw) I'm beginning to get a better handle on it.
At this point, the miniDSPs are simply doing standard IIR crossovers just like you would do with analog devices, and as close as possible to the DSP crossovers I had previously dialed into the Behringer 2496 DEQ boxes (in which I have now turned off the crossover functions). So the change so far is simply moving the same or similar crossover functions to a new set of DSP devices. This should make little or no audible difference.
The minidsp Open DRC 2x2 plugins have IIR crossover function built in (for the FIR type, you need to generate the taps using an external program, then load the taps file into the plugin). I'm doing the exact same crossovers and frequencies as I was doing before using my Behringer 2496 DEQ boxes. With one exception, I'm using a "real" 48dB/octave Linkwitz-Riley high pass cutoff at 17022Hz for the supertweeters, rather than cascading 3 12dB/octave butterworth cutoffs as I was doing before (btw, a cascade of 2x 12dB/octave cutoffs forms one side of a LR4 crossover). So he supertweeter high pass is now a bit steeper, 48dB/octave instead of 36dB/octave, and 6dB down at the crossover point instead of 9dB down. I might have chosen 48dB/octave before but I didn't have that option on the Behringers. Now, on the MiniDSPs, I don't think I have an option to cascade 3x 12dB cutoffs. So their capabilities don't entirely overlap, but the new capabilities are the better ones.
My first listen to pink noise seemed like the bass was too loud and sounding particularly "bubbly" like an aquarium motor, and somehow especially annoying around 60Hz. I had erroneously re-enabled one of the low frequency notches in the Behringer during the changeover, as I determined by checking photos I made in March. Re-disabling that notch at 63 Hz helped a bit. (Sometimes notches make pink noise sound more "tonal.")
But it turned out the main problem was that I had reduced the supertweeter level. Thinking the difference between the old crossover with 9dB attenuation at 17khz, and the new one with 6dB attenuation, I removed an extra 6dB compensatory boost (thinking that wasn't such a good idea anyway). But it turned out, to get the sound back to "normal" I had to dial that exact same 6dB boost back in (I tried other possibilities). Previously with the Behringers I had found up to 9dB boost to be useful, but I had limited it to 6dB. So now the 6dB is equivalent to the 9dB I had wanted to do before but didn't.
I also tried changing the high pass frequency, all the way from 14kHz up to 20khz. Now and in all my "optimal" adjustments for several years I get a tiny 6dB notch at 16kHz. But it turns out if I lower the 17022 even down to 17000 it messing things up bad, or if I move it up things get bad. You would think making the highpass on the supertweeters lower would "fill in" the notch, but it does not work that way at all...the opposite seems to happen, the notch gets worse and turns into a general HF depression from 16kHz up. And similar happens when I move the crossover frequency up. There's obviously some weird cancellations going on here, the point I had already selected, 17022 Hz, is exactly the one that has the least cancellation.
So what's interesting here is that it is showing the exact same kind of sensitivity to crossover frequency as it was doing before, in spite of the changed crossover slope and different hardware. Optimal crossover points are still the optimal crossover points. I am interpreting this as meaning the new system is basically working the same as the old one, all around, which is what I wanted to see at this point. I only want it to change significantly when I move to using FIR type filters.
To really nail down the high frequencies and how to do this supertweeter crossover better I will need much better measurements, etc. 1/6 octave RTA on my phone isn't good enough. And time alignment which I have only approximated.
I listened to "Hanson, The Composer and His Orchestra" where Howard Hanson discusses each part of the orchestra before they play a bit. It was on one of Harry Pearson's lists I came across when skimming old Absolute Sounds recently, and clipped out for reference. I bought every disc on the short list, including the Hanson, and it is as worthwhile as HP said.
Somehow, it was sounding much better last night than two nights before on the old system. Hanson's voice and the whole auditorium space around him and the instruments sounded much more real. During that previous listening session, I discovered my chair had crept backwards about 5 inches and fixed it, but even after fixing the listening position, I didn't remember it sounding this good.
So it's possible something about the new setup, doing the same or almost the same crossovers in new boxes, is better than before. Thankfully it doesn't at all seem to be worse. So now I can move forwards and try different things.
BTW it is far easier to make changes on the Behringer, where you turn knobs and push buttons. The fine control on the miniDSP must be done with an attached computer, and the highly quirky miniDSP opendrc "plug in". (App would be better description, the fact that they call it 'plug in' confused me for years because I was expecting it to load onto the miniDSP unit. But no, the software that actually runs on the miniDSP unit is called "firmware," the program that runs on your computer and downloads filter data to the device is called the "plug in.") So my plan was and remains to keep both the miniDSP's and the Behringers online, using the miniDSP for crossover and FIR-type filters, and the Behringers for IIR filters and testing which is much easier. With the Behringers I can just turn a knob and watch for changes in the RTA. With the miniDSP you have to type in the number, and if you make a mistake the entire crossover could be lost (17000 might turn into 1700 and destroy my tweeters). miniDSP recommends making adjustments "offline." But if you disconnect and reconnect you need to go through another minute of "synchronization." I found the best way is to simply mute the audio when making adjustments through the synchronized miniDSP plug in. When I am sure it is correct I unmute the audio. But with Behringer, I can safely just turn a knob, which is faster and easier when optimizing.
The optimal DSP box would be something more like the Behringer--with a built-in display screen, knobs, and buttons. If the Behringer added FIR capability, and added a few other missing features (steeper cutoffs with adjustable Q, per channel phase invert) it would be way better than miniDSP and I wouldn't need them.
However, just like many times before, I could not easily remove the low pass crossover for the subwoofers from one of the Behringers. Once they start doing a low pass, they never want to stop. Even after power cycling, pressing the "Reset PEQ" button, and other tricks, the Behringer insisted on still applying that low pass filter. I only got it to turn off by doing this: first use the "bypass" mode to disable the PEQ. Then turn the crossover off. Then turn the bypass mode off. And maybe do all that twice.
