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  • jl audio subs

    How do I determine the power I would be giving a 12w7 with a non-jl amp, since the sub runs at 3 ohms. Is this even possible, if so is there a formula to calculate what kind of power i would be drawing?

  • #2
    Ohms Law will help yah there. Youll find exactly what your looking for.
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    • #3
      I know about ohms law and all the electrical relationships, however I do not know if there is a rule of thumb for how amplifiers handle their output. I've seen several different amplifiers with different 2 ohm/4 ohm ratios so it doesn't seem to have a constant relationship, so i don't know how I can determine the output for a specific resistance which is not listed. I also dont' know if 2/4 ohm output amplifiers are stable at 3 or 1.5 ohms.

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      • #4
        On my first system (~8-9 years ago) I ran 2 10w6's off of an alpine v12 amp. Dual 6 ohm voice coils yielded 1.5 ohms (all wires run parallel). I didn't run it like this long as it was only because I had a sub blow on me and took a month or so to get a replacement. I did not notice any adverse effects on sound quality or the amp. Technically the amp was only stable to 2 ohms if I remember correctly. It probably wasn't a smart idea, but I didn't want to be without bass for my tunes. Technically if your amp is stable at 2 ohms, a 3 ohm load won't overload it, but most amps are not completely linear in their power from 1, 2, and 4 ohms. Outside of using a meter to actually test it, there wouldn't be a definitive way of knowing what kind of power you are yielding. You could theorize that it is somewhere close to the middle of the 2ohm and 4 ohm rating as a general estimate obviously.

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        • #5
          Googled Ohms Law
          http://www.google.com/search?hl=en&q=Ohms+Law
          First Link in google
          http://www.the12volt.com/ohm/ohmslaw.asp

          going by that link

          watts=V2 Volts Squared/Ohms

          14.4 squared = 207.36 divided by 3 ohms = 69.12

          so take that for what you will

          If you want more see this http://www.the12volt.com/ohm/page2.asp it is a law so........
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          1994 Mustang GT Punch 240.4 2 12" Kicker Comp SOLD :(

          2006 Suzuki Aerio Sx Kicker KX 650.4 RE 10

          2003 Eddie Bauer Expedition DVD - Navigation Package Traded in for 2008 XL-7 Limited

          Car PC
          Planning

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          • #6
            The problem is the efficiency of an amp at varying loads. Some amps are designed to run better at certain loads (particularly sub amps). Ohms law is based on perfect conditions. Some amps would not be capable of producing (for the price) power that follows ohm's law. They are tailored to a specific load and handle the other loads just for flexibility (even if not truly intended uses).

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            • #7
              Originally posted by racerx3165
              Googled Ohms Law
              http://www.google.com/search?hl=en&q=Ohms+Law
              First Link in google
              http://www.the12volt.com/ohm/ohmslaw.asp

              going by that link

              watts=V2 Volts Squared/Ohms

              14.4 squared = 207.36 divided by 3 ohms = 69.12

              so take that for what you will

              If you want more see this http://www.the12volt.com/ohm/page2.asp it is a law so........
              Think about how what you just explained pertains the the question? All car amplifiers run at 14.4(12) volts, but they sure as hell dont' all put out 69.12 watts at 3 ohms.

              I already said I know about electrical relationships. This still does not explain how much output a specific amplifier puts out at a certain load.

              Like the person above said, it's not linear. Does anybody know if most amplifiers output follows any other type of non-linear regression? Or are they are just determined in the amplifier at design.

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              • #8
                There is no sure proof way other than testing the output with a particular load. Regardless of whether the amps follow ohm's law to a t, it still should be somewhere in between (call it half) the 2 ohm and 4 ohm rating. Things get more interesting when you get into bridging though as most amps do not like to be bridged at anything other than 4 ohms (obviously there are exceptions).

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                • #9
                  Originally posted by zzachattack2
                  Think about how what you just explained pertains the the question? All car amplifiers run at 14.4(12) volts, but they sure as hell dont' all put out 69.12 watts at 3 ohms.
                  Well i assumed you was one of thoose guys who thinks he can get 1000w out of a 20$ ebay amp, so i was trying to prove to you with a Law why those 1000W faceplates are not true I know that it truely matters what your input signal is so if you got a 4V input your looking more like 120W.
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                  • #10
                    Originally posted by zzachattack2
                    I already said I know about electrical relationships. This still does not explain how much output a specific amplifier puts out at a certain load.
                    Then you should know to put a ampmeter in there or simply go by your fuse size you can get a more accurate guestamate. Say you got 14.4V and 40 amps you are at 576W
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                    • #11
                      Originally posted by racerx3165
                      Well i assumed you was one of thoose guys who thinks he can get 1000w out of a 20$ ebay amp, so i was trying to prove to you with a Law why those 1000W faceplates are not true I know that it truely matters what your input signal is so if you got a 4V input your looking more like 120W.
                      And what about amps that are truly 1000+ watts that generate that on the same 14.4V? I'm not an expert, nor do I claim to be, but I do believe you are talking out of your ...

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                      • #12
                        Originally posted by racerx3165
                        Then you should know to put a ampmeter in there or simply go by your fuse size you can get a more accurate guestamate. Say you got 14.4V and 40 amps you are at 576W
                        Right, an mm should be the best way to figure this, but I'd rather know before buying and then finding out.

                        That formula should work, but for amplifiers it tends not to always follow that trend, for instance 14.4V at 40amps at 1 ohm should yeild 576W and 14.4V at 40amps at 2ohms should yeild 288W and 14.4V at 40amps at 4ohms should yeild 144W right? So it follows a linear relationship. However in most amplifiers I've looked at, their 1,2,4 ohm rated outputs do not follow that linear relationship so it must be something designed into the amplifier.

                        I suppose just using those three (1,2,4 ohm) rated outputs into a list on my TI83 and finding the regression which follows it the best(and runs through the origin of course) might be the best way to estimate.

                        Edit: ^^ forgot, the graph shouldn't run through the origin, obviously a higher number, based off the graph it looks like it should creates an asymptote at resistance = 0, so infinity i suppose.

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                        • #13
                          Originally posted by zzachattack2
                          I suppose just using those three (1,2,4 ohm) rated outputs into a list on my TI83 and finding the regression which follows it the best(and runs through the origin of course) might be the best way to estimate.
                          I guess that would be the most logical thing to do. Didn't know you didn't have the equipment yet. If you don't already have the equipment though, why give yourself that many variables and possible problems?

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                          • #14
                            Originally posted by StrataG
                            I guess that would be the most logical thing to do. Didn't know you didn't have the equipment yet. If you don't already have the equipment though, why give yourself that many variables and possible problems?
                            I just want to make sure what kind of power I would be giving a sub, before I actually buy the amplifier and be screwed or disappointed.

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                            • #15
                              Originally posted by StrataG
                              And what about amps that are truly 1000+ watts that generate that on the same 14.4V? I'm not an expert, nor do I claim to be, but I do believe you are talking out of your ...
                              Since everyone has an opinion i guess Georg Simon Ohm could have been thinking outta his ... but who knows they did make it a law unlike the electron theory! To get 1000 watts you have to increase your amperage; wattage and amperage are proportional. Where as resistance and wattage are inversely proportional. But come to think of it i did have Chili.....
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                              1994 Mustang GT Punch 240.4 2 12" Kicker Comp SOLD :(

                              2006 Suzuki Aerio Sx Kicker KX 650.4 RE 10

                              2003 Eddie Bauer Expedition DVD - Navigation Package Traded in for 2008 XL-7 Limited

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