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  • Decibal Output Question

    If for example, a single 10" subwoofer with 350rms watts running through it put out 45dB... what woould the dB output be when another 10" sub is added with 350rms watts running through it also? Is it generally 2x the output in decibals or a little less...?

  • #2
    oops not 45 db.. that was just a random value... A more accurate dB for the 10" is 110.

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    • #3
      If you could double your db's but just adding another 10" sub in there, you'd be the current db world record holder. The answer to your question is the increase would be a lot less than double.
      7" Lilli TS, Soyo K7VME, Semperon 2200, 160GB Maxtor, 512mb PC3200, Deluo GPS, Panasonic Slim DVD/CD RW, Linksys WMP545G , Opus 150w, XMDirect, XP Pro, FP, IG [XXXXXXXXX-] 90%
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      • #4
        its 3db more, double the input and you get a 3db increase
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        • #5
          Originally posted by Nic
          its 3db more, double the input and you get a 3db increase
          some one listened in physics

          if i remeber,, u will double the pressure level
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          • #6
            i have a phyics exam soon :S i wish it was on that stuff tho, its on quantum physics which is hell hard compared to f=ma
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            • #7
              Good luck with your exam

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              • #8
                thanks, i'm gonna need it :P
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                • #9
                  the general rule of thumb is that if you double your cone area you will double your pressure - meaning you will gain 3 db. Also, if you double your power you will double your pressure, meaning an additional 3 db.

                  but there is a point of diminishing returns here.

                  if you look at the SPL vehicles of a few years ago they all used a massive amount of subs and even more power. The gobs have power has stayed the same, but they are now realizing that you can get higher numbers with less subs and a better built box....not to mention a smaller vehicle (less air space to build pressure in)

                  contrary to what a lot of people think, competing in SPL can be a heck of a lot of fun!
                  Jan Bennett
                  FS: VW MKIV Bezel for 8" Lilliput - 95% Finished

                  Please post on the forums! Chances are, someone else has or will have the same questions as you!

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                  • #10
                    yes. double cone area, double power, add 3 db. so a second 10 with a second 350 rms would yield a total of 6 dB on the meter..... max

                    I struggled with this for a long, long time. what it comes down to is that the meter is not a measure of air "pressure" but rather accoustic "energy". Or is it the other way around? Honestly, it doesnt matter.

                    the point of the matter is that the meter will read 6 dB (max) higher when you double your displacement. which is exactly what you are doing by adding both a subwoofer AND doubling power.

                    now, the funny thing to keep in mind is that because of this, while the relationship between excursion and power requirements is still linear, its not a 1 to 1 relationship! Thus, to double the excursion (remember double excursion is double the air motion and therefore a 6 dB gain on the meter!) keeping only one subwoofer would require FOUR times the power! Thus we see that the rule of double power for a 3 dB (max!) gain holds true! assuming the cone of the woofer can actually travel that far!

                    last thing to think about is, why make the distinction between energy and pressure? well, doubling the excursion IS just a 3 dB gain! in pressure (or is it energy? Honestly, it doesnt matter). Thus, we need double the power AND double the cone area to get our 3 dB gain! but the meter will read 6 dB (max!) up.

                    get it?

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                    • #11
                      Originally posted by WhiteRabbit
                      yes. double cone area, double power, add 3 db. so a second 10 with a second 350 rms would yield a total of 6 dB on the meter..... max

                      I struggled with this for a long, long time. what it comes down to is that the meter is not a measure of air "pressure" but rather accoustic "energy". Or is it the other way around? Honestly, it doesnt matter.

                      the point of the matter is that the meter will read 6 dB (max) higher when you double your displacement. which is exactly what you are doing by adding both a subwoofer AND doubling power.

                      now, the funny thing to keep in mind is that because of this, while the relationship between excursion and power requirements is still linear, its not a 1 to 1 relationship! Thus, to double the excursion (remember double excursion is double the air motion and therefore a 6 dB gain on the meter!) keeping only one subwoofer would require FOUR times the power! Thus we see that the rule of double power for a 3 dB (max!) gain holds true! assuming the cone of the woofer can actually travel that far!

                      last thing to think about is, why make the distinction between energy and pressure? well, doubling the excursion IS just a 3 dB gain! in pressure (or is it energy? Honestly, it doesnt matter). Thus, we need double the power AND double the cone area to get our 3 dB gain! but the meter will read 6 dB (max!) up.

                      get it?
                      Errr.... say what?

                      Reading this thread at past 3 in the morning, I just about had a fit trying to figure where the heck did everyone get all their wrong numbers... until I remembered that I am not drawing Bode plots here.
                      so in my world dB = 20 log x which in this case would be 6 (just so you knew why the heck i was confused)

                      For the audio world, dB = 10 log x, hence 3db = 10 log 2 give or take one hundredth.

                      p.s. was that your purpose to make it as confusing as possible? or just a natural gift?
                      I have found you an argument; I am not obliged to find you an understanding.

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                      • #12
                        no confusion, it was written simply to clarify why some say 3 dB and why some say 6 dB. They argue with each other, and they don't realize they are BOTH correct!

                        But, if you'd like to be less rude about it, try replying during normal day hours, rather than 3 AM. A smiley doesn't compensate for poor behavior.

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                        • #13
                          didn't see any rudeness in his response?

                          maybe I'm just dense though....lol
                          Jan Bennett
                          FS: VW MKIV Bezel for 8" Lilliput - 95% Finished

                          Please post on the forums! Chances are, someone else has or will have the same questions as you!

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                          • #14
                            something i dont get here, ive just finished a 10 hour shift so its probably me being stupid

                            if you have an amp and a sub, and you change the amp for one thats twice the power there will be a 3db increase in SPL right?

                            here is where i get confused

                            if you use the original amp and instead of upgrading the amp buy another sub so you have twice the cone area, you guys say you get 3db increase too? how is this possible? 3db is double the power in the air, how do we recieve double the power in the air with an additional sub without extra power? each sub is recieving half the power so would be putting out 3db less, shouldnt this cancel out the fact that there are 2 and give the original SPL?
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                            • #15
                              Originally posted by Nic
                              if you use the original amp and instead of upgrading the amp buy another sub so you have twice the cone area, you guys say you get 3db increase too?
                              almost! we have to assume double Sd and the same excursion. if your first subwoofer has an Sd of 100 cm^2 and your amp pushes it 10 mm, and the upgraded subwoofer has an Sd of 200 cm^2 and your same amp pushes it 20 mm, we've not doubled the air displaced, but quadrupled it, and get a 12 dB (max) gain!

                              so its more than cone area, the bottom line is air displacement.

                              for our original example, remember the relationship of power to excursion is a 2x linear relationship. Thus, to double excursion we need FOUR times the power. So, you asked what happens when we double cone area (add a second subwoofer) without adding extra power, and get a 3 dB gain? lets do some math

                              when we double the cone area at constant power, we halve power per subwoofer, just as you said. But we dont achieve one half excursion until we quarter the power to each subwoofer! Thus, when we double cone area without doubling power, we arent cutting air displaced by half *per subwoofer*, its merely a fraction per subwoofer! add them together, and we arent doubling excursion, but its still greater than simply maintaining the same excursion. and that increased excursion assuming all other factors like efficiency run at 100%, you will achieve a 3 dB gain.

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