Ohm's law has nothing to do with whether or not an amplifier can drive a speaker. While an amp may be able to sustain high power levels into low impedances, that tells you nothing about how well it deals with various amounts and types of reactance across a wide frequency spectrum. It is possible for a speaker to have sharp phase angles at several different frequencies all at the same time.
If you can picture a combination of a "slalom course" AND a "torture test" for amplifiers, that is what some speakers present. As such, you can have a speaker that is highly capacitive at treble frequencies, highly inductive at low frequencies and generates a high amount of reflected EMF ( electromotive force or "voltage" ) all at the same time. All of this can be independent of the amount of "pure" resistance that the amp sees at any given time or frequency. This is why speakers are a VERY complex load and why we don't have specific "tests" that show whether or not an amp can drive every load known to man OR maintain consistent sonic characteristics doing so.
Something else that is not commonly considered is that amplifiers produce LESS power as impedance is raised i.e. kind of the "reverse" of looking for high current into low impedances. After all, impedance raises at the point of resonance on a woofer. As such, power transfer is reduced right at the point that you need it most. Since vented systems typically have MUCH higher impedance peaks at resonance, you have even less power available to control a driver that is already lacking "damping". Even though most manufacturers do not offer power output specs into 16 and 32 ohm loads anymore, one might be able to make a more informed opinion about the overall build quality of an amp if we did know such things.
If you think that this sounds "crazy", take a look at the impedance curve of a vented speaker with a large woofer(s). It is not uncommon to see impedance peaks at resonance along the magnitude of 40 - 100 ohms. What kind of power transfer do you think an average SS amplifier is going to produce into a 50 ohm load ??? Let me tell you, not much.
Most "good" sealed designs keep the impedance of the woofers below 20 ohms, which results in much more accurate and controlled bass. This is due to the increased ability of the amp to transfer power and literally "muscle" the cone when it does not want to see any type of signal at all. After all, resonance is nothing more than the speakers' point of self oscillation. If excited at that frequency, it is literally contributing sound on its' own. It is up to the amplifier to "force feed" it at that point and damp / control the ringing that is taking place. Obviously, a lower impedance at resonance allows the amp to generate more power. This in turn can effectively work to control the speaker and produce greater accuracy.
Having said all of that, rms power ratings are WAY to easy to fudge given the way that the FTC has things set up. I think that measured power output at CLIPPING at various impedances is FAR more revealing of how "sturdy" an amplifier is. After all, this is the point of maximum long term stress for an amp. As such, it is the ultimate test in terms of how much TOTAL power the output devices can pass and how much current the power supply can sustain. If an amp can come close to "doubling down" at the point of clipping from 32 ohms down to 2 ohms, it can probably drive just about any load that you can throw at it. To do so would mean that the amp was as close to a pure "voltage source" as we are currently capable of making. Even if the amp is sturdy enough to do something like this, there is no guarantee that you will like the tonal balance or level of refinement & detail that the amplifier produces. Passing the aforementioned test simply shows that it is capable of "brute force" into just about any given load and does not necessarily mean that it will "sound good". It will however, drive the load that you connect it to. Sean
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