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Thread: jl audio subs

  1. #1
    Constant Bitrate zzachattack2's Avatar
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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. #2
    Constant Bitrate racerx3165's Avatar
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    Ohms Law will help yah there. Youll find exactly what your looking for.
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  3. #3
    Constant Bitrate zzachattack2's Avatar
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    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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    Variable Bitrate StrataG's Avatar
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    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.

  5. #5
    Constant Bitrate racerx3165's Avatar
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    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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  6. #6
    Variable Bitrate StrataG's Avatar
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    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).

  7. #7
    Constant Bitrate zzachattack2's Avatar
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    Quote 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.

  8. #8
    Variable Bitrate StrataG's Avatar
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    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).

  9. #9
    Constant Bitrate racerx3165's Avatar
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    Quote 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. #10
    Constant Bitrate racerx3165's Avatar
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    Quote 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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