A question on v coil resistance (NOT impedance) - diyAudio
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Old 28th August 2002, 02:41 AM   #1
Fossil is offline Fossil  Singapore
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Default A question on v coil resistance (NOT impedance)

For a voice coil with a DC resistance of 8 ohms, if I were to have a input of 1A (AC), is the 8W generated purely heat energy?
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Old 28th August 2002, 03:21 AM   #2
f4ier is offline f4ier  Australia
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No, when we're dealing with AC signals, we will always need to consider the impedance, not just the real (resistive) part alone. In this case, there will be real power and reactive power. The real power can be calculated from voltage*current*Cos x, where x is the phase difference between the voltage and current input.

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Old 29th August 2002, 12:14 AM   #3
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f4ier, I think you missed the exact statement that Fossil made. He said for an input of 1A (ac). Therefore the reactive part, which is in series with the voice coil resistance, does not influnce the amount of heat generated in the voice coil. This is I^2*R, and so is 8W. Of course, there are other sources of dissipation, such as in the mechanical losses of the supension and cabinet, and in the air load resistance, but these are tiny compared to the voice coil.

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Old 29th August 2002, 04:27 AM   #4
Ron E is online now Ron E  United States
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efficiency of a speaker is Sound power out/electrical power in, which reduces to:


100*(1-no) is the percentage of power that goes to heat, assuming the speaker to be a resistor. Since the speaker is not a resistor, the efficiency actually varies with frequency. The true efficiency curve roughly follows the impedance curve, but there is generally no need for you to know that - unless your barroom conversations involve large bets about arcane audio topics.
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