More resistance is less load??

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

Almarg, thank you for your elegant, articulate and patient responses!

there might be measurements that suggest that there were other benefits that made foregoing better measurements at the amplifier worth it.

That measurement is power, which equates to sound pressure. Otherwise there is no real advantage to a low impedance load.

One thing I forgot to mention is how much more important the speaker cable becomes when driving a lower impedance. Into 4 ohms the speaker cable is critical and differences are easily heard between them as a result. Conversely, at 16 ohms the speaker cable is far less important and longer runs can be made with less deleterious effects.

Into 4 ohms, the speaker cable can easily degrade the damping performance of the amplifier. So if your speaker requires a higher damping factor (+20:1) then it will be important to keep the cable as short as possible to minimize its effects. I've seen this have dramatic effects on the resulting bass impact!