Speaker sensitivity and power requirements

Discussion in 'Speakers' started by John H, Apr 30, 2003.

  1. John H

    John H Second Unit

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    What is the formula for calculating the SPL db output of different sensitivity rated speakers with the same power input.

    Is there an online chart availble for reference.

    John
     
  2. Myo K

    Myo K Stunt Coordinator

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    are referring to the whole speaker spl+3 decibles everytime the wattage is doubled?
     
  3. Phil Iturralde

    Phil Iturralde Screenwriter

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    Using a JBL S26 (87 dB) & JBL S36 (90 dB) Sensitivity Ratings as an example:

    Basic rules: (SPL = Sound Pressure Level)

    1: It takes at least 3 dB of SPL for the human hearing to perceive an increase of loudness.
    2: In terms of Power output vs. SPL, to achieve 3 dB increase of acoustic SPL requires doubling (x2) the REC/AMP Power.

    =============================
    Watts...SPL (dB)...SPL (dB)
    1.......87.........90
    2.......90.........93
    4.......93.........96
    8.......96.........99
    16......99.........102
    32......102........105
    64......105........108
    128.....108........111
    =========================
    NOTE: Incorporating an Powered Sub-woofer will remove the AMP/REC requirements & strain.

    So, w/64 watts, the S26 = 105 dB (very loud) and the S36 = 108 dB (very, very loud!)

    To get an little more accurate SPL vs. 5 (or 6) Speakers vs. Room, use C.M.Collins excellent SPL CALCULATOR

    Phil
     
  4. John H

    John H Second Unit

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    So theoretically a loud speaker that is rated at

    Sensitivity: 103 dB SPL, 1 Watt @ 1 meter
    Power Handling: 800w continuous

    with 512w applied should output 130dB @ 1 meter?

    John
     
  5. John Kotches

    John Kotches Cinematographer

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    John,

    Yes.

    However, at the seats is another issue altogether.

    Degradation of SPL is (for most speakers) an inverse square law, which means that for each doubling of distance your output drops by a factor of 2^2 (in other words 4). This correlates to 6dB of drop for each doubling of distance.

    This is great if you're in an anechoic chamber, and few of us are [​IMG]

    There is room reinforcement, which is typically 3-4 dB when all is said and done.

    Regards,
     
  6. Michael R Price

    Michael R Price Screenwriter

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    Speaker sensitivity ratings are sometimes exaggerated. For example, I recall Klipsch stating that they added 4 db to the actual anechoic sensitivity measurement of all of their recent speakers.

    John and Phil,

    Not necessarily. Compression because of heat and speaker nonlinearity is probably a factor especially near the rated limits of the speaker. A simulation of my Adire Kit281s, which are medium sized towers with two pretty solid 8" woofers (rated 150W), indicated the output would be about 2.5db below what's expected with a 100 watt power input at 200Hz, and 3.5db below expected at 40Hz. The speakers have a 2-volt sensitivity of 87db, but putting 128 watts into them would produce about 105db, not 108db as you might guess. From an acoustic power standpoint, that is a significant difference. Additionally, the speakers could produce significant distortion with increased power depending on the drivers, without being driven to near their limits.

    Of course, 105db or anything in that range is pretty darned loud. I think amplifier power is much less of an issue than some might think... especially with high-efficiency speakers. If you want big output it's probably a better idea to just get big and efficient speakers instead of a monster amplifier.
     

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