Question about wattage

[Invidiosulus]

I was just wondering if someone could let me know the formula for figuring wattage if the impedence and voltage are known.

For instance a speaker is rated at an impedence of 8 ohms and its power handling is given as 46.8 volts.

What would the Power handling translate to in watts??

If anyone of you electical engineer types happens to know how to do this that would be great.

I thought I had a book lying around that covered this type of stuff but I don't seem to have the book with me

Peace, Josh

[JohnA]

There are 2 equations and a little judgement involved. The Power equation is:

Pwatts=I*V; I is current (amperage) and V is voltage.

The other equation is Ohms Law: V=I*R; where R is either resistance or impedance. (To be completely accurate, there cannot be a phase shift between the voltage sine wave and current sine wave. If there is, a more complex equation is required.)

Using algebra to substitute values, P=V^2/R (that is V squared).

Judgement comes in because a speaker's/driver's impedance curve is not flat and is likely complex (the aforementioned phase shift). So, your 46 volts causes different power levels at different frequencies since the "R" changes.

P=(46.8)^2/8

P=274 watts

[Invidiosulus]

Thanks John,

I worked on this one while I was on break between classes this afternoon.

It took me a while but I finally came up with 273.78 watts.

I had been forgetting that I needed to know I before I could figure the P.

btw, these figures were from a pdf for the JBL 2025H 12" woofer.

Peace, Josh

[michael hurd]

That may very well be the thermal power limit, but depending on the enclosure design ( sealed / ported ) you may be well past it's mechanical ( x-max ) at low frequencies. Just keep this in mind if you are building or modifying speakers.