Amplifier current vrs watts; why is current more important?

I'm far from an electrical expert but I'm starting to understand the above. So far the criteria I've gathered from research is to look for:

• Amps that double wattage from 8-4-2ohms
• Amps that are 2ohm stable
• Larger power supplies

@christianb5s4 What is important is whether your amp can behave as a voltage source on your speaker. This does not mean it has to double power into 2 Ohms from 4 Ohms at full power even if your speaker does dip to 2 Ohms.

It will have to double power from 4 Ohms to 2 Ohms at less than full power. Do you see the distinction?

The only time there might be a problem is when you are pushing the amplifier hard, like really at full power as loud as the amp will play. All that will happen is if the amp isn't able to do the job at full power it will overload. So just make sure that the amp makes enough power to satisfy your requirements in your room.

IMO/IME its more important to get an amp that sounds like music, rather than to get one simply on its ability to double power as you cut impedance in half. That's a bit more challenging, since to get an amp to double power as impedance is halved will require (most of the time) that the amp also use feedback.

To use feedback properly without the feedback causing brightness and harshness, you really have to jump through some hoops on the design side and frankly, 99% of amps out there simply don't. What good does it do you to have an amp that can double power into 4 or 2 Ohms if it simply sounds harsh and no-one wants to hear it??

 

Unless you have a very benign flat impedance speaker (rare) that doesn't wander to much from being a flat impedance between 20hz to 20khz, only then is an amp with watts but little current OK.

This statement is false.

The impedance *curve* is not so important. The *overall* impedance is, and more importantly than that the intention of the designer of the loudspeaker.  As an example, many ESLs have a fairly low impedance at high frequencies and yet amps with a fairly high output impedance (aka 'low current') can do quite well on them. This has to do with the simple fact that an ESL is fundamentally different from box speakers in that its impedance curve is not also a map of its efficiency. In a box speaker the impedance peak in the bass is due to the resonance of the driver in the box; its much more efficient at this point. ESLs don't behave this way at all and as a result many solid state amps have troubles making enough power into the bass region of the electrostatic.


This is only one example and there are many more, but the bottom line is that you don't need a flat impedance curve, just an impedance that is high enough.


Of course:  ... SETs. They would not exist if the above quote were true. 


Of course no speaker has flat frequency response! Trying to get flat response is a Sisyphean task. 

I am not sure I understand your last statement. Are you saying that zero feedback amps can supply more current and would do better driving low impedance loudspeakers?

No. I am saying that some loudspeakers (like Sound Labs) don't need a very low output impedance in order for the amp to sound right on them. Other examples are most horns, most full-range-driver loudspeakers (like Lowthers) and other speakers where the designer found that he preferred the smoother sound of tubes.

But a monoblock amp like the "Legendary" old Mark Levinson ML2 monoblocks that are only 25w!! into 8ohms, will sound better into them, because it’s said they double their wattage for each halving of impedance all the way down to 1ohm with the current it can generate, so they will stay flat in frequency response, where the 500w’ers will sound like a tone control.

What is important is that the amp behave as a voltage source, not whether it can double full power as the load is cut in half. The latter is a subset of the former.

Of course, a good number of loudspeakers in high end audio don't even expect the amp to behave as a voltage source. That is why there are so many successful  zero feedback tube designs, which behave more like a power source.

As someone who imports and sells a line focused on current vs. wattage, I have a POV. Art Audio amps are biased toward current. That is, our amps are high current and deliver lower wattage vs. many of our competitors. This means that with any given tube, we could deliver a much higher wattage number but opt against it.

This absolutely does allow for better handling of lower impedance speakers. But that is not the only reason and it is not just marketing.

The extra current delivers better frequency extremes. You get lighter & airier treble with better nuance and detail. Bass response is tighter and more refined. Maximize wattage in SET or Push Pull triode and treble gets rolled off and bass gets flabby.

Most of this is false. Current does not exist without voltage; further, wattage does not exist without voltage and current. IOW you can't make one (current) without the others (voltage and wattage).

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. In voltage amplifiers if you can't put enough current through the tube you might lose some high frequency bandwidth; that is why 12AX7s are not a good input tube to use in a power amplifier unless bandwidth isn't important.

'High current' is a marketing thing. As others have pointed out, you don't need that much current to drive high power into low impedances.
If you are looking closely and doing the math, it becomes apparent that the current 'rating' of many solid state amps isn't real. Here's more on that topic:http://www.atma-sphere.com/Resources/Common_Amplifier_Myths.php
Because those high current ratings you often see aren't about the output of the amp, there are tube amps with similar current ratings, such as our own MA-2, which has a 'current rating' of about 50 amps.