determine current needed to drive a speaker

nearownkira

Joined Feb 19, 2008
20
the speaker I bought said something like 800 ohm 5W, 8 ohm 25W or 8 ohm 25W.is there a formula or something to calculate.

mik3

Joined Feb 4, 2008
4,843
the speaker I bought said something like 800 ohm 5W, 8 ohm 25W or 8 ohm 25W.is there a formula or something to calculate.
do you have the reference number of the speaker?

silvrstring

Joined Mar 27, 2008
159
It sounds like your max current rating would be about 1.76 A if you have a typical 8 ohm speaker. P=(I^2)R. In the same way, P=(V^2)/R. So the voltage would be around 14V. That's what your alternator normally puts out.

Are you using an amp?

Audioguru

Joined Dec 20, 2007
11,249
Those are very small 8 ohm speakers. The 50mm one has a max power rating of only 0.25W.
The max power might be its peak power so then its max RMS power from a sine-wave is only 177mW.

Then the RMS current at max power is 149mA RMS.

nearownkira

Joined Feb 19, 2008
20
Those are very small 8 ohm speakers. The 50mm one has a max power rating of only 0.25W.
The max power might be its peak power so then its max RMS power from a sine-wave is only 177mW.

Then the RMS current at max power is 149mA RMS.
how do you calculate all those number?