Results 1 to 5 of 5

Thread: Sensitivity and wattage, difference between main and sub-woofer?

  1. #1
    New Member
    Join Date
    Feb 2022
    Location
    Bangkok, Thailand
    Posts
    6

    Sensitivity and wattage, difference between main and sub-woofer?

    Sensitivity and sub woofer volume

    I need a little help understanding sensitivity when it comes to a 3-way speaker vs a sub-woofer.

    If I have a 92db 2-way speaker (8 inches mid, and a 2-inch tweeter) rated for 100W RMS, on amplifier A (@100 watts this is 112dB). On Amplifier B, I have a passive subwoofer with 92db, 18 inch, rated at 1000 Watt RMS, why would I even turn Amp B (subwoofer) past 100 watts (112dB), as one would want speakers (main 3-way and the sub) playing at the same Db?

    Or why would I choose an 18” woofer with 92db Sensitivity, that is rated at 500 watt vs 2000 watt model, if I am happy with an amp pumping out 500 watts to get to 119db. Do people get the 2000 watt version (and a 2000 watt amp) so they can get to 125dB (a 6dB gain for all that extra money)?

    I am struggling when I look at big sub-woofers and they have such high watt ratings, and their sensitivity is also quite high, so I am wondering what is the point of 2000 watt sub vs 500 watt, as the dB gain is so small.

    Is there something magical about the quality of the sound of some high wattage sub (2000 watt), vs a more modest 500-1000 watt version (other than a 6dB gain)? Or did I misunderstand sensitivity completely and they mean different things between low-frequency subs and higher frequency main speakers?

    Thanks - Pat

  2. #2
    BanHammer™ Manu's Avatar
    Join Date
    Feb 2012
    Location
    Behind you
    Posts
    9,062
    You beat me at using the word ''magical'', be wary of the cheap brands running some ''peak'' specs or things like PMPO watts. What matters is actual loudness output. I think you are indeed asking yourself the right questions.

    so they can get to 125dB
    In the western world, most clubs have a limiter fitted somewhere in the chain. Since covid, most bars have been told to set the limit at 85dB. The only one time I heard of anyone going at 125 dB actually measured, it was a Motorhead live show. Absolutely not recommended as it will inflict ear damage within seconds. The pain threshold is 120.

    If I have a 92db 2-way speaker (8 inches mid, and a 2-inch tweeter) rated for 100W RMS, on amplifier A (@100 watts this is 112dB). On Amplifier B, I have a passive subwoofer with 92db, 18 inch, rated at 1000 Watt RMS, why would I even turn Amp B (subwoofer) past 100 watts (112dB), as one would want speakers (main 3-way and the sub) playing at the same Db?
    It's more complicated than that, frequency range needs to be accounted for and you don't want speakers to overlap each other's frequencies. Besides, an 18 inch woofer coupled some 8 inch mid tops will create a gap in the low mids/bass

  3. #3
    The power density of music program material doubles with each octave decrease in frequency. That means if you need 100 watts above 100Hz you need 400 watts to handle from 50Hz to 100Hz, assuming equal sensitivity from the sub and the main.
    Bill Fitzmaurice
    Bill Fitzmaurice Loudspeaker Design
    www.billfitzmaurice.info/forum

  4. #4
    New Member
    Join Date
    Feb 2022
    Location
    Bangkok, Thailand
    Posts
    6
    Quote Originally Posted by Bill Fitzmaurice View Post
    The power density of music program material doubles with each octave decrease in frequency. That means if you need 100 watts above 100Hz you need 400 watts to handle from 50Hz to 100Hz, assuming equal sensitivity from the sub and the main.
    That is a great response. Much appreciated.

  5. #5
    Member
    Join Date
    Jan 2014
    Location
    Ottawa Ontario, Canada
    Posts
    2,009
    Quote Originally Posted by Uprightfan View Post
    Or why would I choose an 18” woofer with 92db Sensitivity, that is rated at 500 watt vs 2000 watt model, if I am happy with an amp pumping out 500 watts to get to 119db. Do people get the 2000 watt version (and a 2000 watt amp) so they can get to 125dB (a 6dB gain for all that extra money)?

    I am struggling when I look at big sub-woofers and they have such high watt ratings, and their sensitivity is also quite high, so I am wondering what is the point of 2000 watt sub vs 500 watt, as the dB gain is so small.
    You have to account for SPL loss over distance which is -6dB for every doubling. The rated sensitivity of a raw driver is usually at 1w input and 1m from the cone, so at 2m away that 92dB driver is only producing 86db, at 4m it's down to 80dB. For live sound applications in large rooms or outdoors this becomes a really big deal, so speakers with both the highest sensitivity and highest power handling are selected.

    Quote Originally Posted by Uprightfan View Post
    Is there something magical about the quality of the sound of some high wattage sub (2000 watt), vs a more modest 500-1000 watt version (other than a 6dB gain)? Or did I misunderstand sensitivity completely and they mean different things between low-frequency subs and higher frequency main speakers?
    A drivers sensitivity and power handling say exactly nothing about the sound quality it produces, it's brand and relative cost are much better indicators.
    Paul O'Brien
    Old Tech Guy
    www.Techott.com

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
a