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Speaker Impedence

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  • 24-11-2016 10:16am
    #1
    Heighway61
    Registered Users Posts: 1,966 ✭✭✭


    An amp I'm considering buying spec's 180W/Ch into 6 ohms. What would the W/Ch be into my 8 ohms speakers?

    I've emailed the manufacturer but it can take up to 3 days for a reply.


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    #2
    endacl
    Registered Users Posts: 22,237 ✭✭✭✭endacl


    Maths, dear boy. Maths is your friend...

    https://www.techwalla.com/articles/how-to-calculate-speaker-wattage


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    #3
    Heighway61
    Registered Users Posts: 1,966 ✭✭✭Heighway61


    Thanks. Does that tell me how much wattage the amp puts into the speakers?


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    #4
    Heighway61
    Registered Users Posts: 1,966 ✭✭✭Heighway61


    Manufacturer got back to me. It's 135W/Ch into 8 ohms.


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    #5
    ZENER
    Registered Users Posts: 6,163 ✭✭✭ZENER


    endacl wrote: »
    Maths, dear boy. Maths is your friend...

    https://www.techwalla.com/articles/how-to-calculate-speaker-wattage

    I think he's referring to powered speakers and even at that he's totally wrong. The figure he arrived at in his example is the power consumption and not the power output of the amplifiers. Amplifiers are never 100% efficient, I'd estimate about 50% to 70% at best depending on which class they use.

    OP - even an 8 ohm speaker isn't exactly 8 ohms, this is just a nominal impedance for comparison purposes and the real impedance depends on the frequency it's measured at.

    If the amplifier delivers 180W into 6 ohms then the voltage and current in the circuit can be calculated:

    Voltage = Square root of (Watts x Ohms) = square root of (180 x 6) = ~ 33V

    Current (I) will be V/R or 33/6 = 5.5A.

    Power (W) = VxI = 33 x 5.5 = ~ 180W

    For an 8 Ohm load: The voltage swing of the amplifier is taken as the constant so we will use 33V as our figure and get:

    I = V/R = 33/8 = ~ 4.1A

    Therefore the Power at 8 Ohms would be:

    V x I = 33 x 4.1 = 135 Watts !

    P.S '~' = approximately. I = current in Amps (A). R = Resistance in Ohms.

    Amplifiers are complicated things to calculate for as designs can vary therefore these calculations are at best estimates.

    .... now for homework calculate the power at 10 Ohms ;)

    Ken


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