Expanding the Class D Conversation: How Would You Characterize Their Differences?

it seems counterintuitive that one would distort so much more than the other as to make a readily audible difference.

@devinplombier I don't see what is counterintuitive. The ear uses higher ordered harmonics to sense sound pressure; since it has over 120 dB range, it has to be very sensitive to their presence. On top of that, the ear uses harmonics to tell the difference between sounds- like that of a clarinet vs a trumpet or strings. To do that it has to be sensitive to the differences since there are a lot of sounds in the world :)

So now we're going to add some higher ordered harmonics (as that is what you usually see when the load impedance goes down or when the amp has to deal with strange phase angles in the speaker). In a good high power solid state amp, that's not going to be much; keep in mind the ear is optimized to pick up those harmonics. The ear will interpret that as brightness, harshness and likely sounding louder due to the loudness cues higher ordered harmonics provide.  

How much that happens is a different matter, but its measurable in all amps even at low power. As a result a simple way any speaker designer can make their speaker seem to be more relaxed and detailed (two good things to have at the same time) is to keep the impedance up and the load easy. 

So I don't see what is counterintuitive.

@atmasphere 

Distortion can be audible, I get that and I totally agree. The point I question is whether low impedance alone can cause amplifiers to distort, as long as amps are similarly matched with their loads.

Not to put too fine a point on it, an amp rated 40W at 8 ohms might need 4W to achieve a certain SPL with a high-efficiency 8 ohm speaker. It would therefore operate at a 10% load, based on its 40W rating. 

Whereas another amp rated 800W at 2 ohms might need 80W to achieve the same SPL from less efficient 2 ohm speaker, yet operate at the same 10% load based on its 800W rating. I know it’s more complicated than that, but you get my point.

I understand that if one attempted to drive speakers B with amp A, the latter will distort like crazy, clip all over the place, and possibly self-immolate; although that would be the operator’s fault, not the speaker’s.

However, and that’s the counterintuitive part, if amp A and amp B are driven at the same percentage of their respective rated loads, what would cause the powerful amp to distort more than the lesser one?

The point I question is whether low impedance alone can cause amplifiers to distort, as long as amps are similarly matched with their loads.

@devinplombier All amps make distortion. When driving a lower impedance load, all amps make more distortion; ’matching to the load’ has nothing to do with it, although there are better matches for some amps and some speakers. 

When you compare apples and oranges like that it can be confusing. To understand how this works, the 800W amp driving 2 Ohms will make more distortion doing that than it will driving 4 Ohms, and will be even less distortion driving 8 Ohms, all while making the same power.

The 800 Watt amp might be lower distortion than the 40 Watt amp or it may not. That depends on the design of the two amps; an entirely different subject (I think we can agree that a 40 Watt amp is likely to have a very different design from one that makes 800 Watts). But in either case, to minimize distortion low impedances should be avoided. 

@hilde45 

I'm getting my hands on an AGD to try against the NAD M23.

Do you use a switcher?

@bartsw No, I don't use a switcher. Don't want it in the signal chain, plus I want to use the same exact cables.