Reaching the limits of my PB-10 ISD?

Discussion in 'Speakers & Subwoofers' started by Vaughan Odendaal, Jul 18, 2005.

  1. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Hello everyone,

    I got an SPL meter today, and I calibrated my system. It's not the Radio Shack meter, but a different model altogether. All speakers are set to 75 dB's, and I calibrated the subwoofer to about 72dB's. I assume that that is accurate, given the inaccuracy of the meters reading at the lowest frequencie.

    I played around with the subwoofer today, testing it, hammering it, pounding it; with the most demanding material that I currently have. The ring drop did it.[​IMG] I played the scene at -10 from reference, and the bass was almost nonexistant. I tried -12, and it was slightly better. I backed off the volume to -14, and it had deeper, harder hitting bass. I eased off the volume to -18, and I almost got a feeling-in-the-gut type of response from the subwoofer. It was strongest at this volume.

    Putting my head to the port, the air rushed out incredibly quickly, so I assume that I've reached the low-end extension of the sub. Impressive, however I am a little disappointed that I couldn't put it up any louder.

    Some scenes I can play a lot louder than the ring drop scene and the bass plays progressively louder. Like the Sauron fight. When he strikes the armies, I could hear and almost feel the bass. I could play this scene at -15 and it was really impressive. Increasing the volume lowered the bass level considerably, however.

    That is what I'm finding so far with my PB-10. At it's limits, it doesn't just stop playing louder, but it actually goes softer. I could tell with the ring drop scene that if I played the scene at a louder level, that it would be a punch to the gut feeling. My PB-10 couldn't give me that in my 3400 cubic foot room.

    At -10 from reference, there have been a few scenes where the impact is not as great if I had lowered the volume by a few dB's. Is it time for another one?[​IMG]

    PS Could anyone please tell me how low the ring scene goes? I don't like looking at those charts, so if anyone could explain it to me in simple terms (in hertz), I would appreciate it.

    --Sincerely,
     
  2. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Anyone?
     
  3. John S

    John S Producer

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    I will only say, I am all about dual 12" driver subs and 15" single driver subs these days.


    I just don't see 10" and single 12" subs cutting for very many people I know anymore at all.
     
  4. Wayne A. Pflughaupt

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    The PB-10 indeed has a built in limiter.
    The bass definitely has some impact when the ring hits the ground, but you’ll probably have to have a subwoofer/acoustical space ratio on the order of a car stereo to get a “punch in the gut” feeling. John's right, it’s asking too much to expect any 10” sub, even one as capable as the PB-10, to deliver high-impact bass at the lowest frequencies in a room that size.

    Regards,
    Wayne A. Pflughaupt
     
  5. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Hi Wayne,

    That’s impossible because that’s not how a limiter works. A limiter is like a “brick wall” for dynamic range. E.g., output dead stops at a set point.

    Actually, that is what is happening. Once I have reached the limits of my subwoofer, the bass seems to go softer. I did a test. I played the ring drop scene at -10 and also at -20. At -10, there is hardly no air coming from the ports. There doesn't seem to be a lot a deep bass either. However, at -20, there is a lot of air coming through the ports, and the bass hits 10x harder. How do you explain that?

    I mean, my curtains were moving slightly when the volume was at -20, but at -10, the curtains weren't moving at all. There was barely nothing at -10.

    --Sincerely,
     
  6. Wayne A. Pflughaupt

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    My first thought was “don’t be fooled into thinking the bass is reducing when the level of everything else increasing,” but the air flow from the ports is a puzzlement. I suggest calling SVS and see what they have to say.

    But anyway you cut it, it’s not enough sub for your room.

    Regards,
    Wayne A. Pflughaupt
     
  7. Edward J M

    Edward J M Cinematographer

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    Actually the limiters in the PB10-ISD amp are pretty sophisticated. They have attack, sustain, and continuous power parameters that are adjustable during the design/testing phase.

    I have seen the same behavior from the PB10-ISD; the limiters will actually overcompensate and reduce SPL considerably if the input signal is excessive.

    Anyway you cut it, output compression is occuring, and you are astutely observing its effects. There will be a noticeable reduction in both deep extension and sound pressure.

    Wayne is right on - the higher frequency scenes can be played louder before compression occurs because they are less demanding on the subwoofer. Compression will always occur first at the deepest frequencies. The Ring Drop BTW is centered at about 24 Hz.

    Operate the PB10-ISD at the MV setting where no output compression is occuring, and this will provide the most satisfying and realistic presentation. If your preferred playback level is inconsistent with the clean/uncompressed limits if the PB10-ISD, then you need to add another subwoofer (this will give 6 dB more output), or buy a larger and more capable model.

    FWIW, it would take about four co-located PB10-ISD to equal the sheer output capability of one PB12-Ultra/2 in the 20 Hz tune. But four PB10-ISD would actually be cleaner. I'm still waiting for someone to try this (a 2x2 stack of PB10-ISD); it would be a really lethal combination. [​IMG]
     
  8. rob-h

    rob-h Second Unit

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    My PB10-ISD's definitely lose punch if they are over driven. I Currently have 2 and maybe adding at least one more in the next month or so. I like this approach much better then going to one large sub.
     
  9. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    The Ring Drop BTW is centered at about 24 Hz.

    But this worries me. Isn't the output limits of the PB-10 quite a bit below the 24hz region? I'm just wondering. I mean, will scenes that have lower bass information in them, like, for instance, 20-15hz bass scenes, be able to play louder than the 25hz+ frequencies because the sub is tuned quite a bit below that?

    Am I correct? Because you say that I should play the subwoofer where the least amount of power compression is. But that can be difficult. I mean, one scene that I can play with no power compression or dynamic restrictions at, let's say, -12 on the master volume, won't be the same for another very demanding scene, like the ring drop scene.

    I mean, if my subwoofer wimps out at 16-18 from reference with the ring drop scene, then how are other subwoofers going to fare? According to Tom V, this subwoofer is about equal to the improved version of the old CS 20-39. Look at the 25-65hz output readings from TN. It's a heck of alot of output there. And that's a room more than double my size.

    Shouldn't my subwoofer be more capable in the 25hz region or is it at it's best below that region?

    --Sincerely,
     
  10. rob-h

    rob-h Second Unit

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    Vaughan, what SPL are you measuring during the ring drop scene?
     
  11. John S

    John S Producer

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    I am replacing subs for people right and left these days.
    It is the most under configured piece in most systems. I think that ring drop and other key scenes in a variety of modern movies is what is driving these replacements for the most part.

    I think the days of anything small are over for anybody but apartment dwellers where the living situation is the limiting factor.

    As I like to put it, best extension and accuracy doesn't do anything for you if your sub just can't handle the demand / room size.

    Just an opinion as always.
     
  12. rob-h

    rob-h Second Unit

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    The bass above 20hz is of course going to be a few db higher. look at the response curve. It should not be really noticeable for a given input signal level. The problem is the signal level varies from scene to scene. That's how the engineer controls the impact of the scene. You can try decreasing the gain or dropping the sub level on the receiver a few db.
     
  13. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Thanks. To be honest, I haven't measured the output at the seats yet, but how do I do it?:b Must I use A weighting, set to fast? I'm not entirely sure.

    Rob-h, since you also have the PB-10, please tell me how loud yours goes before it wimps out on the ring drop scene. So far, the loudest and lowest bass that I have heard in LOTR is when Sauron is overlooking the armies (it lasts for a split second), when he hits them with his mace, and when the ring drops.

    I haven't seen the other portions of the film yet, as I haven't had the time for it. I guess that having my subwoofer compress the signal is better than bottoming out the unit.

    BTW, does anyone know what the THD limits are for the PB-10 ISD once it's LF limits are reached? Ed, I think you said in the review that it's distortion is low even at it's limits. Perhaps you could expound on this.

    Thanks.

    --Sincerely
     
  14. Edward J M

    Edward J M Cinematographer

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    There is not much I could add here that isn't already in the review. With steady sines, I couldn't push the subwoofer to 10% THD in the 20-22 Hz region before bumping the amp limiter. There are other methods to measure THD besides using steady sines, but I did not employ them.
     
  15. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    So the limiter in the PB-10 acts almost like a servo? So at my subwoofer's limits, it won't play higher than 10% THD? If that is the case, then cool.

    Why don't all the other SVS subwoofers employ this sophisticated limiter? I mean, keeping the subwoofers distortion levels down to 10% is ideal, isn't it?

    --Sincerely,
     
  16. Edward J M

    Edward J M Cinematographer

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    No, it's not a true servo design, but the limiters in the PB10-ISD are very effective and it's almost impossible to bottom out the woofer or truly hurt it.

    You can induce port chuffing if you overdrive it on a scene with a lot of loud content in the 17-22 Hz region, and (as you know) it can certainly be pushed into output compression if overdriven.

    But you need to recognize what this subwoofer can accomplish for the $$, and keep things in perspective. A second unit colocated will give you another 6 dB of clean/uncompressed output, which will be quite noticeable. If you find yourself continuously probing the limits of a single PB10-ISD in that size room, I suggest purchasing a second unit at least.

    Eventually you will determine exactly how much subwoofer is needed in that size room to provide you with clean/uncompressed bass at your preferred playback levels. Until then, have fun on the journey! [​IMG]
     
  17. Edward J M

    Edward J M Cinematographer

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    All powered SVS subwoofers employ similar limiters. They just happen to work exceptionally well in the PB10-ISD.

    Holding distortion to below 10% at the very deepest frequencies is a very good goal. Distortion at higher frequencies is typically much less than 10% at any reasonable playback level. The 20-40 Hz octave will always present the most challenges to any subwoofer; the 40-80 Hz octave is a breeze in comparison.

    Remember that many commercial subwoofers (including some very big and well regarded names) will hit anywhere from 30-60% distortion at moderate playback levels in the bottom octave.
     
  18. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Cool. Thanks, Edward. I think I will be buying myself another PB-10. In the future, I probably would go with four of them.

    I don't know what the difference would be going from a PB-10 to a PB-12/plus, (the next logical choice in my mind) but I would like to keep distortion levels down to a minimum at it's operating limits. And integrating the PB-12/plus into my room would be problematic at best, I think.

    As you know, Ed, my goal is still achieve the lowest distortion while maintaining high output in the lowest frequencies. I'm just thinking to myself that if I've reached the limits of my subwoofer with the ring drop scene in LOTR, then I can't imagine how soft the same scene must play on all other subwoofers as reviewed by Tom Nuisane.

    Remember that thread of mine concerning maximum clean output? Well, if my subwoofer is far superior in clean output to, let's say, an M&K MX-125, then surely the output at the lowest frequencies are going to be underwhelming with that subwoofer?

    The thing is, the output, to me, wasn't that loud. -18 from reference isn't terribly loud. Granted, I wouldn't be able to get that loud with my parents in the room, but still.[​IMG]

    I'm just trying to get an idea of how my subwoofer would stack against the competition.

    --Sincerely,
     
  19. Vaughan Odendaal

    Vaughan Odendaal Second Unit

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    Rob, could you please tell me how loud your SVS goes before it starts to compress in your room on the ring drop scene? Thanks.

    PS A question for anyone; if I got myself a BFD, and, for example, I managed to tame a few big peaks in my subwoofer's response (or my room's response), does that mean that I can play my subwoofer louder before the onset of compression?

    Thanks.

    --Sincerely,
     

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