SVS PB-10 Decay time measurements

Discussion in 'Speakers & Subwoofers' started by Mike^S, Mar 22, 2005.

  1. Mike^S

    Mike^S Stunt Coordinator

    Joined:
    Dec 10, 2004
    Messages:
    84
    Likes Received:
    0
    Trophy Points:
    0
    Hey guys, you know that review that IG/COF did on the PB-10? You know how he said that the decay time was slow and he proved it by showing his 30hz decay test and that it took 1.5 seconds to reach down to 37dB? Well you know what? I just tested my PB-10 and I can't hear anything at 37dB. In fact I couldn't even hear a 30hz test tone at 55dB!!! So who cares if it takes another 0.7 seconds to go from 55dB to 37dB? I can't even hear that! And I don't think there is anything wrong with my hearing.
     
  2. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    25
    Trophy Points:
    0
    Location:
    NorCal
    Real Name:
    John
    Details. Who cares how things measure out, all that matters is how it SOUNDS. [​IMG] I'm happy with the way mine sounds. Now if I could get my room to cooperate...
     
  3. Mike^S

    Mike^S Stunt Coordinator

    Joined:
    Dec 10, 2004
    Messages:
    84
    Likes Received:
    0
    Trophy Points:
    0
    Well that's why I wrote this. cof/ig said that the PB-10 sounded boomy to him and his evidence was his decay measurements. Well IMO, his evidence proves nothing. btw, I care about how things measure out. How it sounds and how it measures are closely related. In this case, however, even though cof/ig measured a longer decay below 55dB, that does not matter because you can't even hear 30hz below 55dB. You can see on his graphs that they decay measurements above 55dB are just fine.
     
  4. Edward J M

    Edward J M Cinematographer

    Joined:
    Sep 22, 2002
    Messages:
    2,031
    Likes Received:
    0
    Trophy Points:
    0
    Yes, many things can be measured that are not audible under normal listening conditions. I'm not saying this was necessarily the case with COF/IG - it's just a general observation.

    Typically room decay is higher in amplitude and longer in duration than the resonances from the subwoofer itself, so low level decay byproducts will typically be overshadowed by the room (and by the source material too).

    Ilkka will tell you that the most respected European audiophile magazine evaluates spectral decay to -25 dB. I use a slightly different twist - I measure to -35 dB (relative to the signal level) just to show the actual resonances, and then comment on the amplitude and duration.

    Adopting the European magazine's criterion as a guideline, if the resonances don't exceed -25 dB in amplitude, I don't worry too much about their audibility under normal listening conditions. [​IMG]

    With that said, a well built and resonant-free enclosure is standard operating procedure in the subwoofer industry; it's simply good engineering practice.
     
  5. Jack Gilvey

    Jack Gilvey Producer

    Joined:
    Mar 13, 1999
    Messages:
    4,948
    Likes Received:
    1
    Trophy Points:
    0

    That might have occured to anyone who managed to think through the hysteria.
     
  6. Ilkka R

    Ilkka R Second Unit

    Joined:
    May 19, 2004
    Messages:
    270
    Likes Received:
    0
    Trophy Points:
    0

    Yes, Hifi-lehti (Hifimagazine) uses these limits: -25dB, 0-60ms, 20Hz-200Hz. Check for example these measurements from Velodyne DD-15. These are done in an anechoic chamber so they are not comparable with ones done in-room.

    COF/IG did get some weird results from his measurements, but I believe that they are not very accurate. Maybe Ed could do a re-run?
     
  7. AlanZ

    AlanZ Screenwriter

    Joined:
    Sep 15, 2002
    Messages:
    1,336
    Likes Received:
    0
    Trophy Points:
    0
    Can someone please translate for the technical-impaired? Is there some practical issue with the damn thing or not?
     
  8. Jeff Gatie

    Jeff Gatie Lead Actor

    Joined:
    Aug 19, 2002
    Messages:
    6,531
    Likes Received:
    15
    Trophy Points:
    0


    The review in question called the decay time a negative aspect of the PB10. He qualified this by citing the sub had a measured decay time of 1.5 seconds when measured at an output level of 37dB (37dB is approximately -48 dB from average dialog reference or -78 from subwoofer peak reference). The problem with calling this a deficiency or a negative is that 37db is not a level people listen to a Home Theater at and is for all practical purposes, inaudible. The reality based opponents in this thread are saying that the measured decay at 37dB has about as much to say about a sub's performance as it's measured output at 0dB, which is to say nothing. Most reviewer's testing of decay goes no lower than -35 to -25 from reference, which would be around 50 to 60 dB average volume, so 37dB is too low to care. I agree with them.
     
  9. AlanZ

    AlanZ Screenwriter

    Joined:
    Sep 15, 2002
    Messages:
    1,336
    Likes Received:
    0
    Trophy Points:
    0
    Thanks, Jeff.....much appreciated.
     
  10. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    25
    Trophy Points:
    0
    Location:
    NorCal
    Real Name:
    John

    Sorry, should have said "who cares about that particular instance, as long as the sub sounds good." which it does. I don't see how anyone could call this sub boomy. It's far from it.
     
  11. Lewis Besze

    Lewis Besze Producer

    Joined:
    Jul 28, 1999
    Messages:
    3,134
    Likes Received:
    0
    Trophy Points:
    0
    Once again somebody is trying to qualify his subjective remarks with some "faulty" data.Anyone has a link for this IG/Cof?
     
  12. Edward J M

    Edward J M Cinematographer

    Joined:
    Sep 22, 2002
    Messages:
    2,031
    Likes Received:
    0
    Trophy Points:
    0

    COF/IG used software that measures total amplitude vs. time. In comparison, the ETF-5 is a true 3-D spectral decay plot. So they really aren't comparable....

    With that said, I'm not doubting what he measured, and I don't want to try and duplicate his experiment and verify the data.

    You can't run spectral decay for subwoofer resonances inside a home, or the room will give false positives. So it's either an anechoic chamber or ground plane outside.

    The noise floor outside (even on a quiet, calm day) typically hovers around 45 dB anyway. The spectral decay data is only reliable if the test floor is well above the ambient noise floor.

    Say the ambient noise level is 45 dB, and the tester wants a 15 dB safety cushion between the noise floor and the test floor. For a -35 dB spectral decay evaluation, the test volume would then need to be 95 dB.

    Eventually the tester will run into practical limits when trying to evaluate progressively lower test floors. Either the test floor and the ambient noise floor will get dangerously close to coinciding (thus corrupting the data), or the required test volume will exceed the linear capabilities of the subwoofer and/or software. Either extreme is unacceptable.
     
  13. Ilkka R

    Ilkka R Second Unit

    Joined:
    May 19, 2004
    Messages:
    270
    Likes Received:
    0
    Trophy Points:
    0
    Yes, I didn't mean that you should try to duplicate his test. I meant that you could measure PB10 and see how it performs in general. I know you don't have one right now, but maybe someone nearby does?

    One thing about levels used. Different levels give different results (lets assume that we measure in very quiet environment). The higher the levels are the more box, driver(s), port(s), PR's resonates and therefor gives different decays. Of course ideal subwoofer should have same spectral decay at all levels under its limits, but in real life that is not true.
     
  14. Wayne A. Pflughaupt

    Moderator

    Joined:
    Aug 5, 1999
    Messages:
    6,187
    Likes Received:
    51
    Trophy Points:
    9,110
    Location:
    Katy, TX
    Real Name:
    Wayne
    There’s a link to his review in the subwoofer face-off in my signature.

    Regards,
    Wayne A. Pflughaupt
     
  15. Mike^S

    Mike^S Stunt Coordinator

    Joined:
    Dec 10, 2004
    Messages:
    84
    Likes Received:
    0
    Trophy Points:
    0
    nm
     
  16. Edward J M

    Edward J M Cinematographer

    Joined:
    Sep 22, 2002
    Messages:
    2,031
    Likes Received:
    0
    Trophy Points:
    0

    Yes, there are some changes in the spectral decay signature that vary with level. But the basic fingerprint is retained unless the subwoofer is grossly overloaded. The nice thing about ETF-5 is that it reads out the optimum test range, and will also inform the tester if the signal strength is too low/high. And I test all the subs for SD at approximately the same test volume for consistency.
     

Share This Page