I think practically speaking, the amp produces Volt-Amps, period. It's the load that determines what percentage of the VA's turn into Watts.
Most definitely, a speaker load would be considered an inductive reactance, due to the back EMF produced by the speaker cone return. So, the power factor will be less than 1 for an amplifier-speaker circuit. This means that although the amp produces a rated voltage and a rated current, the actual power consumed by the speaker is much less.
In large industrial/commercial distribution systems, power factor correction is often applied at the service entrance with banks of capacitors. This is because the utilities charge much more if the power factor is less than 0.9 (in most cases). This occurs often in the case of manufacturing plants, where the windings in many motors that exist throughout a mfg plant add up to a significant inductive load.
Essentially, poor power factors by the end users mean the utility must install a much larger base of power generation. So, it's in everbody's interest to correct for power factor. In my early days of consulting engineering, I sometimes helped audit power consumers for ways to reduce the power factor and lower their utility bills.
In the case of speakers, I believe a Zobel network performs the same function: a capacitor is added to counteract the effect of the inductive speaker coil. This ensures that the amp is delivering as much power as it can, rather than wasting VA's against a reactive load.
|