More resistance is less load??

^^ Yes. Take a look at the specs and you will see.

almarg - believe it or not I didn't "realize, the signal provided to a speaker consists of various frequency components each of which is AC (alternating current)".

I'm kind of amazed, now, at how little I know and how little I questioned. This stuff is actually quite fascinating.

Ok, here's another question: why can't the resistance from the speaker, that the amp relies on be built into the amp itself? Why build a product that has a vulnerability even though the manufacturer knows the amp will be paired with an unknown speaker, of unknown quality and impedance?

Jim, yes, any frequency other than zero Hertz (which is DC) is alternating current. And of course a music signal nearly always consists of a mix of a great many AC frequencies that are simultaneously present, at a wide variety of "amplitudes" (i.e., strengths, or magnitudes).

why can’t the resistance from the speaker, that the amp relies on be built into the amp itself?

In order for a speaker to absorb electrical power, some fraction of which it converts into sound, it has to have resistance. And for it to absorb a reasonable amount of power when provided with voltages that are reasonably practical, that resistance has to be relatively low (e.g., in the vicinity of 4 or 8 or 16 ohms or so). If a similar resistance were placed into the amp, the resistor in the amp would absorb power but convert it into heat rather than sound. So that resistor would serve no useful purpose, but would reduce the amount of power the amp would be capable of providing to the speaker.

Best regards,
-- Al

almarg - ok, here's a variation of the question. When building an amp, couldn't the manufacturer's assume the worst - that speaker resistance, while "typically" 4-8 ohms will occasionally get very close to zero and build the amp on that basis?

Hi Jim,

As a consequence of the equations that were cited earlier for the relations between power, voltage, current, and resistance, it can be inferred that delivering a given amount of power into 8 ohms requires much more voltage and much less current than delivering the same amount of power into a very low impedance, such as 1 or 2 ohms or less. While conversely delivering a given amount of power into a very low impedance requires much more current and much less voltage than delivering the same amount of power into 8 ohms.

And, hypothetically speaking, if the load impedance were to truly approach zero (i.e., a true short circuit), the amount of current required to provide any voltage and deliver any power would approach infinity.

For an amplifier to be able to deliver amounts of power that are generally desirable into both 8 ohms and very low impedances it therefore has to be able to supply BOTH very large amounts of current and relatively high voltages. To be able to do that it will have to be much larger, heavier, and more costly than would otherwise be the case. And most likely sonic compromises would result as well.

There are some amps that can supply substantial amounts of power into impedances of 1 ohm or thereabouts, and in a few cases perhaps into even lower impedances, but in all of those cases I am familiar with the amps are big heavy monsters, which consume large amounts of electricity, generate a lot of heat, and don’t necessarily sound as good as many other amps that are in the same price range.

Regards,
-- Al