# determine current needed to drive a speaker

Discussion in 'Homework Help' started by nearownkira, Apr 1, 2008.

1. ### nearownkira Thread Starter Member

Feb 19, 2008
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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.

2. ### mik3 Senior Member

Feb 4, 2008
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do you have the reference number of the speaker?

3. ### silvrstring Active Member

Mar 27, 2008
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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?

Feb 19, 2008
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5. ### Audioguru New Member

Dec 20, 2007
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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.

6. ### nearownkira Thread Starter Member

Feb 19, 2008
20
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how do you calculate all those number?

Apr 20, 2004
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