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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
carlsbad2's avatar
carlsbad2
2,023 posts
 

I didn't read the wordy versions above, or I quit at the first incorrect statement in each of them.  Here is the simple version:

 

Amp WPC is a rating taken at nominal resistance, that is, optimal conditions.  

Now if resistance goes down, to keep voltage constant, amperage has to go up.  If amperage can't go up (low current amp), then voltage, and therefore power, will be limited by the capability of the amp.  thus you need an amp capable of providing high current for speakers with low impedences.

Jerry

thecarpathian's avatar
thecarpathian
5,061 posts
 

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

Thanks."

My take;

If you’ve got a bunch of big honkin’ capacitors in your amp, you’ve got a high current amp.

If you don’t, you’ve got a low current amp.

Hope that’s not too highly technical for everyone!😃

sns
3,754 posts
 

Not only low impedance  but impedance curves matter greatly as well.

erik_squires
16,695 posts
 

Your understanding of the electrical formulas are correct.  Impedance curves are most easily obtained from Sterephile reviews, such as this one.  The top chart shows an impedance curve.

This particular speaker shows a minimum impedance ~ 6 Ohms, and IMHO would be a good candidate to be called an 8 Ohm speaker.

I also want to caution you that I've seen dynamic speakers designed specifically to be hard to drive.  They are sold as "revealing of an amplifier's capabilities."  Well, that's great but it doesn't help them play music.

Of course, some speakers just have bad crossovers, and some like the Apogees or electrostatics just can't help it. 

To add to your electrical understanding, amplifiers have an output impedance that is also not usually flat.  Often they are better in the mid to bass than the treble.  That's something else that should be considered.  ESL's are hard to drive in the treble.  A "weak" amp will lose treble output. 

steakster
1,998 posts
 

@gregm +1

High current is shorthand for delivering more current on demand.  The P=IE formula remains the same.

An imperfect analogy would be gas engines.  A Ford F-350 will go 60 mph.  A Ford Fiesta will also go 60 mph.  When towing a trailer with a 2 ton load, the F-350 will deliver more power on demand than the Fiesta.   When going uphill, there will be less strain on the bigger engine – while the smaller engine might crap out.

Some speaker designs have low impedance dips at certain frequencies which require more instantaneous current delivery.   The goal is to reproduce the authentic sound of the musical instrument: such as a thwack of a snare drum, the gut punch of a kickdrum, the  shimmering of cymbals or the blaaat of a trumpet.

Matching the speaker and the amp is important.  This is where transient response is involved.

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