Amplifier current vrs watts; why is current more important?

The late Charles Hansen used to say that an amplifier is basically a power supply design in which the supply is being modulated by an external musical signal.  

Wattage measurement is a static number that has no "time" variable, but in music, timing is everything.  Current is also a static variable without "time".  For example, if you say I want 7Watts but it could mean it will take 2 secs or 10 secs to get 7 watts.  In an orchestra crescendo, you need 7 watts right away.  A good amp will supply that 7 watts almost instantaneously whereas an inferior amp will not, therefore reducing the impact of the music.

A better metric for measuring an amp transient response is called "slew rate", that is how fast it responses to a change in input.

For any given amp, the slew rate will respond proportionally to the load (impedance) of the speaker.  That is the higher the load (higher impedance), the faster the slew rate.  That is why speakers with low impedance, you need higher power amp so that the slew rate will be adequate otherwise the music won't have any dynamic.  

As an analogy using cars, watt is like a car speed, whereas slew rate is car acceleration.  

Let's say you have two car: a good old American muscle car and a Ferrari.  Both cars may be able to do 150mph, but the Ferrari will accelerate to 150mph much faster than the muscle car which is what most people want.

Andy, are you addressing the Q of the OP or changing the topic?

I think the OP wants to know why current is more important than "watt", but I think what he really wants to ask is why two amplifiers may have the same "wattage" rating but one amp may appear to have more "power" than the other.  He is thinking maybe because one amp has more current therefore more power.  It is only partly true.

My response was meant to say the "current" itself may actually not it, but a better characterization of how "dynamic" the amp is by using slew rate measurement.  

So in that sense, I was responding to his "inquiry" but may be in a different way. 

Current is only of import when speakers dip to low impedance or have challenging phase angles, or both. Otherwise it is of little consequence.

There are so many wrong's in this statement.

Also a read from Pass Labs First Watt will help.  

Your typical amplifier outputs volts

It may be a bit oversimplification.  Two power amplifiers that have the same power supply voltage may not have the same output current.  Ultimately it's neither the voltage or current, but the overall design that determines the quality of the sound.

You may have a massive 800W power amplifier with massive output current but it may not provide quality music reproduction compared to a more modest 250W amp.

Two power amplifiers that have the same power supply voltage may not have the same output current.

It should say that 2 amps with the same power supply voltage may not be able to deliver the same amount of current

Hm ... are these two statements not the same? 

Similarly, extra current (if it were somehow to exist) does not affect bandwidth. What **does** affect bandwidth is output transformers; generally speaking the bigger you make them the less bandwidth you get.

This seems to be limited to tube amp which requires an output transformer.  Interestingly, atmasphere specializes in OTL tube amp which does not need an output transformer.  But this seems to be getting away from the OP original question.  

rbstehno,

I guess no analogy is perfect!  It's up to one's choosing.  

arguing against viridian is like talking to a brick lols.