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Home Forums DIY Speakers and Subwoofers Need help understanding DIY subwoofer amplifier power requirements.

  • Need help understanding DIY subwoofer amplifier power requirements.

    Posted by Juan on September 8, 2023 at 6:12 pm

    Hi first of all, I’m a novice on the topic willing to learn. I noticed that for diy subwoofer high-powered amplifiers are used. At high level analysis, My understanding or assumption is, to compensate the DSP applied (ie a -6 db at 90hz with a q of 1) lo flatten the frequency response at 75 db you would need more power to get to the original 81 db.

    i.e. originally 81 db required 100w ( i know, very inefficient, its just hypothetically)

    75db 100w -> 78db 200w -> 81db 400w

    can some one confirm or deny or enlighten me?

    thanks all

    • This discussion was modified 3 weeks, 4 days ago by  Juan.
    Chedwin replied 3 weeks, 4 days ago 3 Members · 3 Replies
  • 3 Replies
  • TVOR-Ceasar

    September 8, 2023 at 9:04 pm

    I think you meant 75->78->81. No biggie.

    Generally, a 3 dB sound level change, positive or negative, is a factor of 2 X’s the power. So +3 dB is 2 x the reference level, and -3 dB is 1/2 x the reference level.

    JL Audio has a good page on it here:

  • Juan

    September 8, 2023 at 9:26 pm

    Thanks for the correction. I overlooked my post.

    so in this regard you are confirming my assumption? This would be the reason for high powered amps?

    • Chedwin

      September 8, 2023 at 10:16 pm

      @Juan The page @TVOR-Ceasar linked is all the answer you will need


      +3db acoustic power is 2x electrical power
      +6db acoustic power is 4x electrcial power
      +10db acoustic power is 10x electrical power

      To answer the reason why high power amplifiers are used for subwoofers, the lower a frequency the larger the driver needed to reproduce that frequency cleanly at high SPL. Larger drivers have more mass and therefore a higher voltage is required to move the speaker driver to achive a target SPL vs a smaller driver. Higher volatages need higher power rated amplfiers with larger capacitor banks to safely handle the transiet loading of low frequency content. In my pro audio background I often see high frequency compression drivers running around 10-15V under high SPL usage whilst 18″ subs can be hitting 80V on the amplifiers ouput side.

      Its not just in the DIY audio side high power amplifiers are used for subwoofers it is simply a forced requirement of their intended use case