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

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. 

@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.

@mclinnguy This statement is false:

A Coda 16 has 280,000 uF of capacitance and can deliver 100 amps of current, per channel.

Here’s why. As @immatthewj points out, the power the amp makes is equal to the current times Voltage. The actual Power formula is 1 Watt= 1 Amp x 1 Volt; IOW power is equal to Volts x Amps. A derivative of this formula that includes Ohms is Power= Ohms X Amps squared.

Giving the Coda the benefit of the doubt, that it can drive a 1 Ohm load, at that impedance the power is equal to the amperage squared. So I think you can see the Coda, as good as it is simply can’t do that; that’s 10,000 Watts! That sort of current through the output section of the Coda would heat the output devices to slag.

That value is actually the amount of current that flows when the power supply is shorted for 10milliseconds so has nothing to do with output power nor the impedance it can drive.

My take;

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

@thecarpathian Please read my above explanation about why this isn’t true. The reason to have lots of capacitance in the output section is to prevent the amplifier from modulating the power supply which can introduce IMD. It has nothing to do with the output power otherwise. We make some amps that have large 3" diameter caps which have a lot of storage; as much as any solid state amp of the same power. But being tube amps they are not likely to be considered ’high current’.

What is important for most speakers is that the amp can behave as a Voltage source; IOW that it can produce the same output Voltage regardless of the load impedance. No amp can actually do that of course but over the range of impedances most speaker present there are quite a few amps that do behave as Voltage sources on them.

But to be clear a tube amp can behave as a Voltage source too as long as it has enough feedback to allow for a low output impedance. But instead of doubling power as impedance is halved it cuts power in half as impedance is doubled.

@atmasphere ,

I’ve always thought the higher the capacitance reserve an amplifier has, the more amps it can deliver when needed. This isn’t correct?

I read what you wrote, but frankly really didn't understand it!

I’ve always thought the higher capacitance reserve an amplifier has, the more amps it can deliver when needed. This isn’t correct?

@thecarpathian That isn't correct. By that metric our MA-2 can deliver more amps that most solid state amps of the same power. The output power is determined by the power supply Voltage and the resulting current that the output devices can handle. So that has a lot to do with the power transformer and the dissipation the output devices will see. In short- its complicated.