4 ohms.......

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  • 05-23-2006, 11:45 PM
    swwdts
    4 ohms.......
    Ok, if I had an amp/subwoofer w/ a 100 watts peak in 4 ohms load .Would it go down to 75watts peak in an 8 ohm load?
  • 05-24-2006, 04:00 AM
    N. Abstentia
    It does not really matter, since the peak rating is useless. You need to look at the RMS rating which gives you the useable power. If it's 100 watt 'peak' it's probably actually 40-50 watts RMS.
  • 05-24-2006, 08:06 AM
    swwdts
    My owners manual lists that the FTC rating is less than 1% THD @ 56w @ 100hz @ 4 ohms. So, 8 ohms would make it only a 28 watt @ 100 hz @ 8 ohms ? Is that right? If it is the amp is going in Mondays trash pick up...
  • 05-24-2006, 09:35 AM
    N. Abstentia
    1% is a lot of distortion, and it should be rated at 20-20khz instead of just at 100hz so it's not rated very good. What kind of amp is this? Sounds like a Pyramid car audio amp :)
  • 05-24-2006, 02:39 PM
    swwdts
    It is an amp built into my KLH subwoofer.The KLH subwoofer is on its way to the dump & I am keeping its box for the new subwoofer that I am replacing it with.The replacement sub will be from Parts Express on pg 287 there is a Dayton loudspeaker w/ a 5 year war. on it.For those of you who have the book it is the QT255-4 subwoofer.Item # 295550 . Anyway,I have never heard of that brand I hope they are good.I bought the KLH at H & H Gregg .The bass sounds like a boom from a 1980's SEGA console.No boom just bleepThey said that it was a good one.I'll never shop there again.
  • 05-24-2006, 03:15 PM
    N. Abstentia
    Well it probably WAS a good sub for the price you paid. What was it? $89? What did you expect?

    And, is this the same .6 cu.ft. box you asked about before? If so, don't expect much difference. You'll need 1.5-2.0 cu.ft to get deep response out of it. If you can go 2 cu.ft. I'd go with a 12"
  • 05-24-2006, 05:35 PM
    swwdts
    Yah it is still the down firing 10" sub box. w/ 0.67 cubic air space.I found a 10" MTX that would work but,it was over $ 150.00.Due to current cash flow I have to stay under 150....My 8" sony ( 100 watts RMS ) subwoofer hooked up to my pioneer 600watt amp set on - 20 can make my living room windows vibrate. In a room 20' L x 12' W anything over a 10" powered subwoofer would be over kill.
  • 05-24-2006, 06:24 PM
    Smokey
    Quote:

    Originally Posted by swwdts
    Ok, if I had an amp/subwoofer w/ a 100 watts peak in 4 ohms load .Would it go down to 75watts peak in an 8 ohm load?

    A simple calculation will answer your question.

    First we need to find the voltage..

    Voltage (squared) / resistance = watt
    voltage (squared) / 4 ohm = 100 watts
    voltage (squared) = 4 ohm x 100
    voltage (squared) = 400 volts
    voltage = 20 volts

    Now that we have voltage (assuming the Amp's rail voltage doesn't change when load is varied), we can plug in the 8 ohm to find watts. So....

    20 (squared) / 8 ohm = watts
    400 / 8 = 50 watts

    So 8 ohm load will result in 50 watts output.

    You can use the formula below to plug in any numbers :)

    http://www.sengpielaudio.com/OhmschesGesetzA.gif
  • 05-24-2006, 07:14 PM
    N. Abstentia
    Problem is..there's no way of knowing how much of that 50 watts is wasted as heat and distortion.
  • 05-24-2006, 08:28 PM
    paul_pci
    All calculations aside, the bottom line is that there is no need to keep the sub amp.