how does current work in an amplifier?

EXAMPLE
Think of it this way--a garden hose of 1" diameter (diameter represents resistance) is presented with X amount of water (water represents current), and under these parameters, waterwill squirt 25 Feet.
Let's lower the resistance (increase the hose diameter to 4") and present the same amount of current (Water)....now the water simply trickles out the end of the hose.
So, and hopefully this is somewhat clear, the less the resistance of the speaker (impedance) the more current the amplifier has to product for all else to be equal.
In the absence of proper current the amplifier can and probably will, go into 'oscillation' trying to produce current with the transistors, for want of a simple example, and literally burn itself up.

Current is the ingredient which 'drives' the speaker, so to speak. For convenience in 'matching' speakers with amps, Dsper, manufacturers rate the speakers as to their impedance. Generally giving a 'nominal' figure. Speakers are generally REACTIVE not purely resistive, meaning that at different frequencies they present different resistance it's an approximation.
An amplifier is thought of as 'high current', if it keeps doubling into half resistance. Example: 100 WPC into 8ohms, 200 WPC into 4 Ohms, and 400 WPC into 4 Ohms.
The less resistance the speaker presents, the more current the amplifier must produce, in order to 'fill the pipeline.'
I hope this is clear.

If you have further questions you can reach me at lrsky@insightbb.com or I can supply a phone number, and we can talk in person. Actually, matching speakers and amplifiers is an important goal in audio in a host of areas, this being just one.

Good listening.

Larry

A formula that might help is the following:

Current in Amps SQUARED = Power in Watts DIVIDED by Resistance in Ohms

For comaprison:
100 watts into an 8 ohm speaker requires 3.54 Amps
100 watts into a 4 ohm speaker requires 5.00 Amps

Not sure if this helps at all, but...

I can't give you an in depth explanation. But if you look at the listed specifications for any given amp you should see the Amperes (Amps) that the Amplifier is capable of delivering. You should find a specification for both continuous and the peak number of amps the amp can produce.
The cut off, delineating a high current from an ordinary (non high current) amps has not been officially established AFAIK. But you can do your own informal survey of the big amps with reputations for handling demanding loads and following those specs as the amplifiers get progressively more powerful, to get a general idea of the range you are considering.
My own completely arbitrary idea of the lowest limit for a "high Current Amp" is about 20-30 amps continuous. but be aware their is alot more to it than this single figure.
I am prepared for the onslaught of scientific explanations to follow which will point out the critical importance of other specs to consider. Mine is a simplistic view.
BTW a really big amp will put out over 100amps non peak just so you know. Pay some attention to the slew rate as well which tells you how fast the amp can deliver that power when needed.