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SME

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Everything posted by SME

  1. SME
    Your math is correct, but you are plugging in the wrong numbers. Yes, the amp will be supplying 90 amps to your sub to produce 8000W with 1 ohm. However, it needn't pull 90 amps *from the wall* in order to do so! Simply put, power output = power input * efficiency. So a 90% efficient amp will need to draw 8900W (with rounding) from the wall to supply 8000W continuously. If the mains service is 240V, then that will pull about 33 A. That's far cry from the 90 A you stated. Furthermore, the amp capacitance provides an energy reservoir that allows it to temporarily output more power than it takes from the mains line. This is a big deal because you keep talking about low impedance loads like they require some herculean number of amps out of the wall to provide their rated power output at the low impedance they are rated for. This is not true. 8000W is 8000W as far as the mains supply is concerned. What matters is if the amp is up to the task of supply it for the load that's present. The higher the impedance, the more volts the amp needs to be able to provide to supply that power. The more interesting question is if the amp will misbehave or burn itself up when presented such a low impedance where it can easily be asked for way more power than it is designed to provide. I can't believe I personally wasted so much time researching this issue. Too bad there is, as you say, almost no data to clarify what caused it to happen. That is what we call an anecdote, and a single anecdote does not amount to much evidence at all. There's nothing wrong with reporting that it happened, but it's obnoxious to see this one anecdote used as a stick to beat the reputation of the SP2 repeatedly. And of course, if someone can produce substantial evidence that the SP2 chokes so easily, then we will have more to talk about.
  2. SME
    Your argument is stupid. In so far as mains capability limits performance, supply voltage and amp efficiency will be major concerns. The SP2 runs on 240V and is 90% efficient. Put it on a 30 A circuit, and it can supply something like 5000W continuously without tripping the breaker. Try doing that with a class AB design with ~60% efficiency (generous estimate) that runs on a 120V/30A supply where you'll run out of gas at a measly 1700 W. How much does this really matter? I imagine a lot of amps would overheat before too long with that kind of load. The class D is dissipating something like 600W, which ain't bad, but still requires some serious fan action in a 1 or 2U chassis. The class AB is dissipating more like 1150W. Whew! That's hot! This is a stupid line of argument because the SP2 kicks butt in this category. A more sensible argument is that long term output capabilities aren't that important because the biggest ULF demands typically occur in transients or very short passages. Average thermal dissipation rates are much lower in these cases. Better yet, circuit breakers allow far more current to pass than they are rated for as long as the draw doesn't last too long. IIRC, a couple seconds at 2-3X rated load is not likely to cause a flip. Lastly, to the extent that line sag matters, some amps cope with it better than others, and it is never the "final determinant" so long as the operator is capable of replacing the line with a shorter or fatter cable.
  3. SME
    Dave, what are you trying to say here? You talk about the lack of bridge capability like it's a flaw, when in fact the amps are already bridged internally. And in fact, they bridge into 2 ohm loads, unlike most amps that need 4 ohms to be operated bridged. Or, is there something special about delivering your power into 4 ohm as opposed to 2 ohm? The power supply capabilities are especially impressive. That long duration sweep likely drains all the reserves, so it really measures what the power supply (and the AC supply line) can provide up to the point at which current limiters kick in for thermal protection or to prevent circuit breakers from flipping. As for efficiency, I am fairly certain that the efficiency advantages of class D do not have to do with recycling of back EMF energy, and in fact, the presence of back EMF is a nuisance that appears in their design that is most adequately quelled by bridging the outputs. To have not one but two fully-bridged outputs is an advantage, not a disadvantage. It looks like the SP2 and K10 probably have very similar roll-off characteristics. The signal chain measurements thread shows the K10 down about 3.5 dB down at 5 Hz and 7.5 dB at 3 Hz. That doesn't look too bad at all, of course, assuming the K20 and K10 have identical roll-off.
  4. SME
    Wow, big props to the SP amp! I'm amazed you couldn't get the fans to spin without running a continuous clipped signal into a 2 ohm load. I also like that the amp can drive 2-ohm loads in stereo without issue.
  5. SME
    It ought to considering its size, amp, displacement capabilities. I have a hard time believing their mains speakers can keep the pace, however. Those two 5.25" woofers in the sealed box are likely to come up short when it comes to reproducing upper bass frequencies from 80-150 Hz. I suspect even a single 12" woofer in a 16 Hz ported box would be underutilized in such a system unless the sub level was being boosted. They are 4 ohm nominal impedance, most likely to improve sensitivity, but this rules out use of most consumer AVRs. At least the low crossover between woofers and tweeters near 1 kHz likely mitigates the worst of the issues arising from the horizontally oriented center channel placement. This was probably the primary reason for using a tweeter array with a ".5-way" style crossover.
  6. SME
    Wow, XTZ really needs some help with editing their web pages. My favorite line is in regard to their twisted pair internal cabling: "The construction idea is Zero Noise cable, CMRR (Common Motor Rejection Ratio) (reduction of overhearing)". Yes, please I could definitely use some motor reduction to prevent overhearing. Thank you.
  7. SME
    Interesting. That also means that the measured level will depend on how the data was obtained. If the data is taken straight from the disc, then there's a good chance the dial norm won't be applied, but if the data is sampled from an output on a player (whether analog or digital) then the dialnorm is likely active. This issue probably doesn't impact very many movies since most use DTS-HD MA rather than Dolby TrueHD audio.
  8. SME
    Stereo track? Does this include the LFE channel?
  9. SME
    Unless I've missed something, the best available QSC sub is -6 dB at 25 Hz. I believe all of their designs a ported, hence they roll off very quickly below that point, and there is probably little room gain help there in the large rooms typically seen in high end theaters. I have heard rumors of ultra high end theaters in some major metrpoli like Chicago that offer full bass capability into the teens, but I've never seen confirmation of these claims. As far as I can tell, most theaters are 30 Hz and up with a few of the nicest ones extending down to 25 Hz.
  10. SME
    I didn't know that. It explains why I thought it sounded like garbage. I used a lower playback level than I do for almost any film, and I still found it to be uncomfortably loud at times. It wasn't Star Trek: Into Darkness bad, but it was up there with some of the harshest sound I've heard from a blockbuster movie on my system. I heard hard clipping in the dialog. In later louder scenes, many sound effects were so distorted by compression/limiting as to be unintelligible. Overall, it sounded rushed and amateur to me and made me wonder how the movie won the academy awards for sound. That this new mix may be closer to the theatrical one is intriguing, even if a lot of the low end is gone. Frankly, I don't think it added much in the 5.1 track. I am curious to give this another spin, but like I said, I really didn't like the movie at all. I hated both of the characters especially and found myself hoping they would die so that the movie would be over. I thought Interstellar blew Gravity out of the water in pretty much every category.
  11. SME
    While this is an interesting idea (albeit one that would probably get one kicked out of the theater if caught), I don't believe this would actually be useful. It would be impossible to tell the difference between the soundtrack and the distortions contributed by the theater's equipment and room acoustics. In particular, when trying to determine whether a soundtrack has a 20 Hz filter applied, you won't have any idea because most theaters can't really reproduce 20 Hz at all.
  12. SME
    Considering that a fair bit of the sound design involves a lot of bass at 30 Hz, that's quite tragic. Can they get the academy to revoke the academy award(s) for sound as I seriously doubt that the theatrical track was filtered that way. All of this suggests that they did a completely new mix for the Atmos home release. It would be nice to know why they filtered the bass. Was their sub system not up to the task? Were they trying to avoid distortion on weaker systems? Did someone just apply those filters because of something they read online and shouldn't have believed? At least, it sounds like the rest of the soundtrack is much better. Perhaps I could even enjoy it now, except that I really didn't like the movie either.
  13. SME
    For home releases, I think Atmos has already proven to be DOA. When it was first announced (for the home), I was very skeptical because of all the marketing fanfare coupled with a total lack of technical documentation. The technical details were crucial because, to my best understanding, the Bluray format does not provide enough data bandwidth for a full theatrical Atmos track without compromises. Such compromises could have included use of lossy instead of lossless compression, a reduction in the number of available objects, or even a mix without objects at all. I actually guessed that Dolby had opted for the former compromise, using lossy compression, because it would at least provide a simple path for mastering Atmos content for the home from theatrical Atmos content. Only after all the fanfare did it emerge that in fact Atmos for the home relies on "spatial audio coding", which Dolby stresses is not the same as the matrix-encoding as used for Dolby Pro Logic (and derivatives). Nevertheless, it's definitely not the same technology as is used in theaters, and its use for home mixes may require more cost and effort from the studios than they care to invest for most releases. In my mind Dolby Atmos at home is and always was more of a branding/marketing campaign than a real technology. In contrast DTS:X is yet to be released, and I think it has a lot of potential. Whereas Dolby rushed their solution to the market prematurely (IMO), DTS has had the opportunity to learn from Dolby's mistakes. One of those mistakes, IMO, was to design for the theater without giving consideration to how the technology would translate to the consumer world. DTS is designing DTS:X for both commercial theaters and consumer systems, simultaneously. In this way, they can provide a more seamless authoring experience for studios to create home mixes from theatrical originals. There is also rumor that the DTS:X technology will be "open" in some way, so that perhaps authors will be able to produce DTS:X content without even needing to use DTS's own proprietary tool chain. Many in the industry argue that the reason DTS HD-MA dominates over Dolby TrueHD on Bluray releases is simply the fact that the DTS tools were cheaper, more flexible, and more readily available than the Dolby tools. I will say that Atmos in the theater has definitely been a success so far, and this success has undoubtedly benefited the home viewers as well. Essentially, the Atmos authoring tools facilitate the use of more and better panning effects in mixes. Many films authored in Atmos for the theater have 5.1 or 7.1 home mixes with excellent panning and imaging throughout, despite the reduced number of channels. The addition of bass management for non-front stage channels to the theater setting also encouraged authoring of soundtracks with more bass effects in the other channels and increased bass headroom overall. I believe the Atmos authoring tools supported rendering of object mixes to 5.1/7.1 channels from their inception. It's possible that Dolby improved their down-mixing algorithms between the time that the original and the Atmos-enabled Gravity home versions were released, and this accounts for the improved panning in the latter version.
  14. SME
    Yep. I used to blame a lot of soundtrack quality issues on "made for home" mixes, but I've basically walked back on that opinion in light of the fact that mixes intended for the theater just don't translate well to the home. Furthermore, headroom is effectively more limited for the theatrical mixes, provided that the same monitor levels are used for both. Why? Because the transient sounds in any given mix will sound quieter in a theatrical environment than at home due to differences in "direct+early-reflection-to-reverberant" sound ratio. Based on common recommendations that mixes be monitored 3-6 dB lower than reference when the room is smaller (or 6 dB or more lower on actual near field setups), it is reasonable to assume that theatrical mixes need transients up to 6 dB stronger to achieve the same dynamic impact. In a sense, there's more trade-off between "hot" and "dynamic" when mixing for the theater. I don't doubt that at least some "made for home" mixes introduce additional filtering, clipping, or unnecessary reductions in dynamics. How much dynamics reduction is necessary for a home mix is very much debatable. Home theaters using larger rooms with longer decay times, lower levels of early reflections, and speaker systems with less directivity may need more dynamics to achieve the same impact compared to home theaters in smaller rooms with shorter decay times, higher levels of early reflections, and/or speaker systems with more directivity. Speaker systems with more direcitivty tend to employ horns, and larger diameter and/or greater numbers of woofers. Similar variations exist In actual movie theaters as newer theaters often shorter decay times and therefore need lower playback levels (or some dynamics reduction) for "big dub stage" mixes to translate to them properly. Hence, many theaters either sound too loud (Liemax) or don't actually play at reference. In the long run, I may still want the theatrical mix, if for no other reason than the fact that it's production is more standardized than for any other mix type. I'm currently looking into a more powerful and flexible DSP solution for room correction. If that works out, I hope to experiment with a "room EQ" approach that I hope can correct the translation problem to a large extent and reproduce theatrical tracks in a home environment at reference level while retaining a proper dynamic balance and not sounding too loud. If I am successful, then I will gladly take the theatrical track over a made for home mix, at least unless and until some proper standard is devised for those made for home mixes.
  15. SME
    What kind of filter is it? The original soundtrack had a 15-20 dB shelf below 20 Hz or so.
  16. SME
    Wow, that's bad! I wonder why 25 Hz?
  17. SME
    Do you use R128 analysis to normalize track-by-track with the classical stuff? If so, I think something is off here. In classical music, it's quite typical to have pieces that are almost entirely piano or pianissimo, which may have average level 20-30 dB below that of a typical theatrical track. That doesn't mean it should be played back 20-30 dB higher, at least if you mean to follow the artists' intent. This is what a so-called "normalize by album" approach does for you. It analyzes the whole album using something like R128 and adjusts the playback level of each track uniformly so the piano tracks are distinct from the forte tracks. Note that even high dynamic range digital music is frequently peak normalized, whether directly by analysis and subsequent amplification or indirectly via clipping or limiting. For the better albums, one only hits full-scale maybe once or twice, but that means your system is still being asked to play peaks that it may not be capable of playing.
  18. SME
    Can you name any recordings that you routinely play at 20-30 dB above theatrical reference? That seems a bit exaggerated. For a stereo track that allows peaks of up to 125-135 dB. That seems just a bit extreme, unless you want to hear the concert from the perspective of the percussionist as opposed to the front row seats, for example.
  19. SME
    Maybe so, but it's not common in movies to have strong 16 Hz sustained for such a long time. At theatrical reference, it looks like that pushes 109 dB (or 111 dB, if you use 85 dBC with -20 dBFS RMS pink noise) for a long time. That'll definitely warm up those voice coils.
  20. SME
    Thanks for sharing! I'll have to check that out.
  21. SME
    I totally agree with feeling like I was in the space ship. In the wormhole scene, the sense of motion was quite incredible. I only have a 55" TV at 10 feet away. I can only imagine what it would be like on a large screen. I don't think the spectrograms posted on the thread do justice to what the scene is liked. It just looks like full blast noise centered at 30 and 60 Hz, but it sounded a lot less narrow band and more rhythmic. I wonder if a spec with a shorter window would reveal more? If "Interstellar" were released in 2014, I think I may have given it my "best of the year" vote.
  22. SME
    Thanks! You might also want to clarify the remakes like FOTP and TR with years to clarify which version is being referred to.
  23. SME
    I sure hope so. I watched the trailer for that, and I swear, I've never been scared so much by bass in my room. And that was only the trailer with a 2 channel mix on subs that only go to 15-20 Hz. I have to admit, I'm seriously afraid of that movie messing up my head.
  24. SME
    Interesting. For what it's worth, I did see a few complaints about not being able to hear the dialog posted to the official thread here. Putting aside the criticism about its clipping, this definitely seems to be a hit or miss mix with people. Maybe that is poor mixing in and of itself, since the mixer is supposed to make it sound good on a wide variety of systems. At the same time, I am intrigued that system/room performance makes such a difference with this one. I have noticed that about other recordings I have that I've had the chance to listen to as my system develops. Some things I own sound good no matter how my system is set up, but there are other things that sounded relatively poor in earlier iterations of my system that now sound wonderful to me. I imagine "Interstellar" to be in that category as something I would not have appreciated a year or two ago.
  25. SME
    It's also possible that the speakers are fine but the acoustics just didn't jive with the film's sound presentation. It's been a while since I've been to an IMAX, but don't they have pretty dry acoustics? Actually, I'm thinking their acoustics are all over the map since each one is different. I do think theaters in general have been moving toward drier acoustics, which likely necessitates lower playback levels. I don't think the comparison to TF5 is warranted. To me "Interstellar" is a very macro dynamic film. Much if not most of the film is presented at levels below those of typical action flicks. I heard plenty of clipping in the quieter scenes, but this always seemed intentional and was made to sound consistent with what was being presented. For example, peoples voices clipped akin to radio crackle when they spoke loudly inside their space suits and a digital phone device depicted in the film clipped digitally when one emphasized syllable was spoken. Only closer to the end of the film did the clipping seem to arise due to headroom compromise. Even the organ on its own suffered from some limiting, but considering that it never sounded unnaturally loud to me, it is apparent to me that the film could have used more headroom if it were available. Also, am I the only one who experienced a solid image of the organ in front of me about 100 feet away? I wonder how much that influenced my perception of its loudness. I have often noticed that as imaging improves, subjective loudness often drops a lot. We are much more comfortable with loud sounds when we can make sense of where those sounds are coming from. For what it's worth, I watched this movie at a higher level than I have some other recent films. "The Theory of Everything" got played 1 dB lower, and it was still annoying to listen to at times. I thought that movie had an especially poor mix that sounded very rolled-off. The wife complained about the level early on. And then there was "Titan A.E.", the DTS track on DVD. This movie seems to embody the same attributes as most of the music featured in it. The dialog and sound effects were irritating to listen to at anything higher than what would be 71 dB. Now that's a loudness war track!
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