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Everything posted by andy497

  1. Ages more, and my newborn turned into a semi-autonomous mini-human, and I can turn some attention back to audio. I swapped an aging laptop for a proper desktop HTPC, and many of my measurement problems (particularly with time-alignment not being repeatable) seem to have fallen away. Repeatability is very good, and predicted sweep summations using dozens of biquads across different channels match reality almost exactly. Quick q: Is there a way to export out of MSO into a minidsp compatible import format (i.e. xml)? If not, I may write it. It looks like it still will take a couple step
  2. Cool. Re: horsepower, yeah I found that was the easy part. I have an aging intel i7 for the HTPC, and I found that 64k taps x 7 channels took a few % of cpu. No big deal. The much bigger pain is the video delay, or lack thereof. I went down to 16k taps and am doing everything I can to speed up the audio chain and slow down the video one, but it's still never enough. Jriver, which I love/hate but mostly hate, handles movies fine, but I find I watch a lot more youtube in practice. Adding to that, shrinking buffers too much gives me popping and crackles, and I hate that even more than bad
  3. SME, are you DSPing with IIR or FIR? I was imagining lin. phase crossovers if you're doing complicated mains/subs blending, but at the low frequency end like that you're talking huge numbers of taps and possible major pre-ringing. I'm now very curious what you mean by each crossing mains to each sub differently. Can you elaborate?
  4. Back in college I got to spend a fair bit of time with an NMR (analytical chem version of an MRI, except the center diameter is super focused at maybe an inch or two across). I don't recall the field strength for sure, but I seem to remember 7 teslas, and it needed to be cryogenically cooled 24/7. It was strong enough that the CRT monitors in adjacent rooms had their displays color smeared and contorted permanently. We were required to empty our pockets next door and carefully inspect clothing for any ferrous bits, else we couldn't go near it, although I don't think anyone ever tested
  5. There is so little spider left in that basket compared to the coil, I would think that would severely limit the travel. I wonder what guided them down these design decisions.
  6. I don't see why you can't correct that with FIR. Let's say you want to compensate down to 2 cycles at 20hz = 100 ms. At 44.1 khz sample rate, that's 8,000-ish taps. How many do you have available?
  7. Has any work been done on controlling the boundary layer in ports to delay separation? (e.g. targeted roughness, turbulators, etc.) I know you need to have a precise idea of the Re range, and any given solution will be very specific to that port geometry. Also, I imagine everything may be different in an acoustic resonator; not only is flow not fully developed, it's constantly changing direction. Still, it sounds like an interesting area of study.
  8. Lots of excellent insights andyc56 and SME. I think I found my culprit. I pulled into REW two different "before" sweeps of the same sub, one a day apart of the other but with otherwise identical settings, to see if I could make one look like the other. A simple low shelf (what the internet speculates the THX BGC does) won't do it. At some point, I tried the REW merge A to B function, and it became obvious. When REW realigns the timing of one sweep, it becomes a mirror match of the other. That leads me to believe that BGC perhaps wasn't on and I just had a hiccup with the acous
  9. One week update: Well, I thought things would get easier after my initial 35 sweeps, but the work was just beginning. I have been having a terrible time getting the expected results on a given channel before/after eq. I thought this might be related to my reliance on the acoustic timing feature in REW, but that's working swimmingly. I can run individual sweeps of four subs, then sweep the combined subs, and the computed sum sweep in both REW and MSO precisely matches the actual. In contrast, when I sweep an individual channel, apply a simple eq and sweep again, the results are close bu
  10. Thanks for all your effort andyc56! I've got about 16 hrs into MSO now and am having a bunch of fun. I'm out of town now, but I have three different i7 machines at home which will be cranking on solutions all weekend. Quick q if you have a sec: Is there a way to define global eq constraints? e.g. min/max cummulative boost. I'm limiting individual peqs, but it keeps stacking things and occasionally wants to push one channel up 25 db. For the same config I've gotten nearly as flat with no channel pushed more than 6 db, but i don't have a way to make it prefer smaller effective boosts/cuts.
  11. I can't believe I've never run across that software before or seen the thread on AVS. Very exciting! Getting a proper timing reference in REW has been a major pain in the past, but I'll keep at it. I was very excited about that recent feature since I do hdmi out with a usb mic. However, I've had nothing but problems with the asio half on the two laptops I have. Both are modern windows 10 machines but share the same behavior: I can get 3 or 4 measurements tops, at which point the next sweep has an awful crackling sound. I haven't been able to fix that with adjustments to the latency/bu
  12. That's really interesting about -3 dB in REW. That's typically where I've been measuring. This scope has a half-way decent FFT function, so I'll be interested to see if I can see that as THD in the output compared to -3.5 or -4, though I suspect you could do this more accurately in REW. Now I know to listen for it too.
  13. I'm kinda surprised that audyssey dynamic eq does not do any time-based dynamic compression. In fact, when listening to music with dynamic eq on, I could swear I've heard the pumping effect from the attack/decay triggers getting tripped regularly with the beat. Perhaps it was in the source material, but it seemed to go away when dynamic eq was switched off. That was an unusual occurrence however. Most of the time I like it.
  14. The 31.5 hz sweeps where max output continues for a cycle or more after input stops just boggles my mind. Crazy. And it's interesting that this type of "distortion" slips right by CEA-2010 testing. I guess you'd see that as ringing in a waterfall graph?
  15. I'm experimenting with not just matching/optimizing via a fixed distance delay, but using IIR all-pass filters to mate the group delay of different driver alignments. For reference, I have four sealed subs (4 cubic footish) and two ported (12 cubic footish, ~16 hz tune) in the theater and thought this might be interesting. I started in winisd and played with all-pass parameters on the sealed sim until the system group delay matched with the ported sim. It's possible to get very close with just guess/checking (though it would be nice to write an algorithm to solve for this, particularly
  16. I'm working on my signal chain and thought I could add a few data points here. I don't fancy sweeps, as I was using an oscilloscope to look for clipping/distorted waveforms. However, that saves me having to worry about my loopback measurements and a questionable soundcard. Here's the signal generator from REW out via hdmi into an Onkyo TX-NR809 receiver. screenshot of 5 hz: The yellow boxes at bottom are displaying period, frequency, Vpp, and Vrms. With AVR at maximum possible non-clipped output, I saw 22.5 Vpp (!) at the sub out. In the screenshot you can see that 5 hz was 2
  17. I use https://shapeways.coma fair bit for prints. The quality is very high, but it's still FDM, so things usually have a slightly rough finish. They do a variety of materials including fiber reinforced (extra cost and requires a human to verify your model) and a bunch of metals (speakers still too inexpensive? Try printing the enclosures out of platinum!) It gets pricey fast however, and the maximum dimensions are typically small (e. g. < 30cm), but that's easy enough to check. All of their material pricing is on the site as well, without having to upload a model. All that said,
  18. What's the passive crossover stuff for? I assumed it was all active. Is one of the woofers low-passed to avoid off-axis cancellation or something?
  19. Aw nuts. Yes I suppose bridged would be a problem. It's too bad differential probes are so expensive. Do those flukes have any kind of data out feature? I know my cheapy tekpower does. It's actually pretty decent. I think it captures 10 samples per second if you pick low precision: www.amazon.com/TP9605BT-Cellphone-Connection-Interfaced-Multimeter/dp/B00SGKR9FA
  20. It's part of the design of the scope to have ground terminals of all channels wired together and to the main earth ground. It would be unsafe not to. In the above image, you can see that the black side of probe 2 is on the other side of the load from the black of probe 1, which is your problem. There is huge potential between those two when they are on either side of the measured load. As to why this happens, the resistance on a single probe from + to - (where the scope measures it) should be around 1 megaohm, so it can measure high voltages without things smoking, but the grounds betwe
  21. I imagine a 12K should be able to break-in just about anything you want.
  22. Re: break-in, I don't know how you are going to give them the necessary excursion * time without needing to re-drywall your house or have your neighbors move away. What you need to do is park those things near Xmax in free-air for a few days. So... have you tried wiring each cab with one driver out of phase, just for the purpose of breaking in? You could run all four cabs at once with alternate drivers canceling, and you'd have a whole lot of air whooshing and hopefully little net sound output. The cabs might do some dancing, and you'd want to first find the new shifted impedance max in
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