Speaker Impedence

Heighway61

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.

endacl

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

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

Heighway61

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

Heighway61

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

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