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Question about high current amps versus "not high current amps"

Recently I read a reply to a post about a certain speaker, and the person who replied typed that (and I am going to paraphrase somewhat) the speaker required a high current amp to perform well and it wasn’t the WPC that was important.

Sorry as I am afraid that these are probably going to be  "audio electrical questions for dummies," but here goes:

I vaguely remember being taught the PIE formula, so I looked it up online for a quick review and if I am understanding it correctly,

P (power/watts) = I (current/amps) x E (electromotive force/voltage) .

My first question would be: if I am understanding that correctly, how can wpc NOT matter since watts are the sum of current x voltage? I mean if you have so many WPC, don’t you then HAVE to have so much current?

My next question would be, if I am understanding PIE correctly, is E/voltage going to be a fixed 110 vac out of the wall, or is that number (E) determined by the transformer (so it would vary by manufacturer) and it is that (different transformers that are used in different amps) going to be the difference between a high and a lower current amp?

Or am I completely off base thinking that P is wpc and P is actually the spec in my owners manual that lists "power consumption as 420 watts operate 10 watts stand by"?

And lastly, what would be an example of a high current amp and what would be an example of a low current amp?

Thanks.

 

immatthewj
mclinnguy's avatar
mclinnguy
584 posts
 

I had thought capacitance had to do with instantaneous current delivery as well.

Obviously 100 amps through a 15 amp outlet is impossible for long periods. 

In theory as far as continuous power one can only have 80% of 15 amps x 120 volts = 1440 watts before the breaker trips, assuming the power amp is the only draw on the circuit. I don't know how short this time period is. 

But an amplifier is not a hair dryer, and we are not blowing our speakers or our ears with a sine wave.

@atmasphere so what might be the instantaneous currents provided in music reproduction, even for a few milliseconds? 

 

atmasphere's avatar
atmasphere
11,879 posts
 

so what might be the instantaneous currents provided in music reproduction, even for a few milliseconds? 

@mclinnguy The instantaneous power will be within the output power limit of the circuit. Therefore so will the current (else the amp fails or goes into protect mode). Generally speaking its not that much! On a 4 Ohm non-inductive load 200 Watts will produce roughly 7.07 Amps (200 = 4 times the current squared; IOW the square root of 50). If there's a weird phase angle involved with that impedance in a nutshell it will behave as if the load impedance is lower. So if similar to 2 Ohms then the current is 10 Amps.

So you can see all these wild current claims are not having to do with output power that's actually driving the speaker.

 

westcoastaudiophile
326 posts
 

@dlevi67 +1

amp does deliver current to speaker-load, AND also dampens / controls current from speaker (inductors and capacitors in passive crossover, inertia generated current by drivers), thus higher current than just driving resistive load output stage is needed. 

thecarpathian's avatar
thecarpathian
4,724 posts
 

@atmasphere ,

One more quick question:

What do you mean specifically when you say ’output devices’? The amp itself or certain components within the amp?

Thanks

atmasphere's avatar
atmasphere
11,879 posts
 

@thecarpathian 'Output devices' means components in the output section of the amplifier; usually power transistors mounted to a heatsink. We make both class D amps and tube power amps so in their cases either GaNFETs or power tubes.

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