gain from multiple subs

Discussion in 'Archived Threads 2001-2004' started by mark rush, Nov 3, 2002.

  1. mark rush

    mark rush Stunt Coordinator

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    when I added my second paradigm pw2200 I stacked it on top of the other 2200, it gave about 6db of added output, my question is if I add another 2200 for a total of three subs will it give me another 6db or only 3 db.
    thanks Mark
     
  2. Dustin B

    Dustin B Producer

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    It's definately not another 6dB gain. Another 6dB gain would require going from 2 to 4. Another 6dB after that would require going to 8.

    What you can expect going from 2-3 I'm not entirely sure. I hate logarithms, never really got a proper grasp on them. I think it would be pretty close to a 3dB gain though.
     
  3. JoelM

    JoelM Stunt Coordinator

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    When you add a sub you increase 3DB because of cone area. When you add the same power to each sub it will add 6DB. Example:

    1 Woofer with 400(400x1) watts= 120DB
    2 Woofers with 400(200x2) watts= 123DB
    2 Woofers with 800(400x2) watts= 126DB

    If the paradigm pw2200 has a built in amp then yes it would add another 6db's.
     
  4. Doug BW

    Doug BW Stunt Coordinator

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    Logarithms are your friend! [​IMG]
    Adding a third identical sub should give you about 3.5 dB additional headroom compared to two subs.
     
  5. mark rush

    mark rush Stunt Coordinator

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    Hey thank you all for the info, adding that 3rd sub won't make as much of a change as when I added the second one, maybe I will just bite the bullet and buy two more, four sounds like a nice number![​IMG]
     
  6. steve nn

    steve nn Cinematographer

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    Your a animal Mark.[​IMG] I have thought of this to but I want some variety I think on my next purchase.
     
  7. RichardH

    RichardH Supporting Actor

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    Where is everyone getting this idea that you get 3dB from the double cone area and another 3dB from the double amps??? That is incorrect.

    If you have 1 speaker driven w/ a 100w amp, and then you add another identical speaker driven w/ another identical 100w amp, you get a 3dB increase in SPL. The reason you get up to 6dB in the case of subwoofers is because there is "coupling." In short, the subs are much closer together than the length of the wave they are reproducing, so you get to "cheat" physics in a way.

    Also, if you have 1 speaker driven by a 50w amp, and then you swap out for a 100w amp, you will get 3dB more (assuming the speaker can handle it fine).
     
  8. mark rush

    mark rush Stunt Coordinator

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    I know if both my subs are stacked, it sounds louder than if they are seperate from each other, anyone else with some more light on this?
    Mark
     
  9. RichardH

    RichardH Supporting Actor

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    Do you mean it's louder when they're stacked vs. right next to each other sitting on the ground?
     
  10. mark rush

    mark rush Stunt Coordinator

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    meaning if stacked versus one on each side of a main speaker{7 foot spread}
     
  11. RichardH

    RichardH Supporting Actor

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    Oh, well, yeah, that's correct then. If you have them stacked or right next to each other, then you're getting more of that "coupling" that I mentioned. If you have them 7 ft. apart then you're not getting the extra help from coupling.

    Plus, you could be cancelling out some frequencies if the subs are working against each other. It is possible to get 2 subs in a room such that they are both contributing nicely, but it's difficult. So, for the most part, find the place w/ best response and shove both subs there.
     
  12. mark rush

    mark rush Stunt Coordinator

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    thanks for the info, I am still learning, new to high end audio and video
     
  13. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    I have my 2 subs separated by 8 feet, both are in opposing corners on the front wall. After taking a frequency sweep, the average SPL the 2 subs added over having just one sub was 5 decibels.

    The least SPL you can get from adding a 2nd subwoofer is 3 decibels. (Given that the phase is correct)

    The acoustic coupling occurs when the sound waves from both subs combine to form one big sound wave. This can add an additional 3 decibels (at most) to the spl. This explains how you are getting about 6 decibels from adding the 2nd sub.

    If you space two subwoofers 6 feet apart, the coupling frequency is at about 121hz (transition frequency). Space a sub about 3 feet, then the coupling frequency rises to about 242hz. (This is why I still get acoustic coupling SPL even though my subwoofers are spaced about 8 feet apart)

    When the distance between subs gets too great, the acoustic coupling will no longer occur. So 2 subs that are spaced 50 meters apart will only have coupling at about 4hz.

    If you added 2 subs to the 2 subs you have now you'd get at least 3 decibels. That means adding a third subwoofer will add a little less than 2db and with acoustic coupling it could possibly total to about 3 decibels.

    Of course I didn't use math because nobody else seems to want to either. I guess I could add that rooms add their own effects since vibrating walls can absorb bass therefore making it harder to estimate.
     

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