I want my Subwoofer Flat

Discussion in 'Speakers & Subwoofers' started by Chase_Smith, May 13, 2004.

  1. Chase_Smith

    Chase_Smith Auditioning

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    Not like a pancake.

    The tools I have right now are Sound and Vision Home Theater Tuneup and a Radio Shack SPL meter.

    I've been getting mixed reviews on what level I should set the subwoofer to in order to set it to reference level. Not +3 above reference, I want it as flat as possible without introducing the BFD or any other equalizers.

    So, what do I do? All I care about is setting the average LFE output to match the standard Dolby reccomends. I also just ordered the "Explore Our World" DVD which is supposed to have a rather simple dedicated LFE test.

    So, suggestions?
     
  2. Mike SJ

    Mike SJ Supporting Actor

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  3. Chase_Smith

    Chase_Smith Auditioning

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    Well, some are saying that the SPL meter is less sensitive, so that when it reads 85db on the meter, it's actually 88db, so you need to reduce it by 3.

    Others say that the meter is too sensitive, so when it reads 85db the sound actually being put out by the subwoofer is 82db.

    So, I guess my question in its most basic form is, what SPL reading(number) should I get from Avia when the sub is properly set to 85db(actual SPL)?
     
  4. Mike SJ

    Mike SJ Supporting Actor

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  5. Chase_Smith

    Chase_Smith Auditioning

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    That's my confusion.

    I know the offset numbers for the SPL meter, but I'm not sure if they even apply here.

    So, with the SPL meter, I should simply set the sub level to +3db than the reading I'm getting from the surrounds?

    Sounds simple enough. Can you explain why the subwoofer is set higher though? It does have to do with the SPL Meter being inaccurate, right?



    Haha, I realize that. I just need a sanity check. I have a $35 Radio Shack Analog meter.
     
  6. Kevin G.

    Kevin G. Second Unit

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    I think he's referring to a post a while back that mentioned that Avia was off on their callibration disc.
    It said that the setting for reference was too low, I believe.
     
  7. Lew Crippen

    Lew Crippen Executive Producer

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    edit--Oops, looks like you already knew all this. Sorry

    A couple of things Chase.

    First, if what you want is to get the ‘average’ SPL level of your sub to match the rest of your system that is one thing—but to get it for its entire range is quite another.

    To begin, that SPL meter (I wrote some of this already today) is less sensitive to the lower bass frequencies than other. This means that when you calibrate your system, when you get your meter to indicate that it is at the same dB level as the rest of your speakers, it is actually louder.

    You can compensate for this by setting your sub to an indicated SPL that is lower than your other speakers (I’m not familiar with the VE disk, so I can’t comment on any specifics pertaining to its use). A reasonable number to use is 3dB. But this depends on the test tone generated. If the VE disk generates specific frequencies, here are some corrections for the Radio Shack SPL meter.

    20 Hz +7.5dB
    25 Hz+5 dB
    32 Hz+3 dB
    40 Hz+2.5 dB
    50 Hz+1.5 dB
    63 Hz+1.5 dB
    80 Hz+1.5 dB
    100 Hz+2 dB

    Now even if you had an acoustically perfect room, most subs are not flat over their intended frequencies. Some subs (the UFW-10 is one) have a one-band, built in equalizer, that will correct one peak (or valley, but it works best for flattening a peak). AV123 has stated that their UFW-12 will have a five-band equalizer, which ought to fix almost anything. If your sub does not have a built-in equalizer (and most do not), you can always purchase a stand-alone equalizer.
     
  8. Chase_Smith

    Chase_Smith Auditioning

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    See why I am confused? There are so many conflicting reccomendations I'm not sure who to believe.

    You basically told me to aim for a reading of 82db, while Mike told me to get a reading of 88db.

    I swear I'm going to turn my sub level to +10 and watch Darla tap on the tank until my head explodes.

    [​IMG]
     
  9. Lew Crippen

    Lew Crippen Executive Producer

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    I’m not sure that is what Mike meant. In fact you run your sub 3dB hot, when you set it at the same meter reading as your other speakers.

    Now I could be wrong, but I took my correction numbers from the UFW-10 manual and checked over on the AV123 site. I can only say that these numbers are consistent with what I have read elsewhere.
     
  10. Chase_Smith

    Chase_Smith Auditioning

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    Okay, I trust you. I'll set my sub so the needle touches 82db at it's lowest point.

    Thank you VERY much.
     
  11. Mike SJ

    Mike SJ Supporting Actor

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  12. ScottCHI

    ScottCHI Screenwriter

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    because the meter is LESS sensitive to the lower tones, you must OVER-compensate by adjusting your sub to a HIGHER spl reading than the other speakers when calibrating with avia. and i'm talking the test tones on the disc, here. not correction factors for "pure" 30Hz, 25Hz, 20Hz, etc. tones.

    capeche?

    (confuses me too)
     
  13. Cam McFarland

    Cam McFarland Supporting Actor

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    Which means it (the sub) is actually going to be LOUDER than everything else, right..?

    [​IMG]
     
  14. Lew Crippen

    Lew Crippen Executive Producer

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    Perhaps I’m confused, but consider the logic.

    Consider two different SPL meters: one the Radio Shack under discussion and another that measures all frequencies perfectly. We generate a test tone of 85dB. The perfect meter measures 85dB. The meter that is less sensitive does not ‘hear’ as loud a test tone. It shows a reading of 82dB (for example). If we had a third meter that was more sensitive, it would consider the test tone to be ‘louder’ and measure it at 88dB.

    Therefore, when adjusting volumes to be equal, when the less sensitive meter reads 85dB we have boosted the sound level to 88dB in order to get the meter to what appears to be the proper level.

    In the case under discussion, we don’t have two meters, but one measuring different frequencies. It is a ‘perfect’ meter when measuring normal frequencies and a ‘less sensitive’ one when measuring the lower bass frequencies. Therefore, getting the meter to read the same for both frequencies results in a3 dB boost to the lower bass notes.

    QED.
     
  15. Lew Crippen

    Lew Crippen Executive Producer

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    Yes--see above.
     
  16. Cam McFarland

    Cam McFarland Supporting Actor

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    If the gain on the sub is turned up to get the low(er)
    notes to 85db on the meter, it will be louder everywhere,
    as it was actually playing at 85db, only the meter didnt
    know it cause its hearing was impaired, right.....lol
     
  17. Mike SJ

    Mike SJ Supporting Actor

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  18. Cam McFarland

    Cam McFarland Supporting Actor

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    You answered as I was typing, lol....
     
  19. Cam McFarland

    Cam McFarland Supporting Actor

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    Thats absurd......everybody knows there was no need to
    measure sound 30 yrs. ago!



    [​IMG]
     
  20. Mike SJ

    Mike SJ Supporting Actor

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