No matter what kind of amplifier you have, if sound quality is your goal, it will be at a disadvantage driving a load like this, even if the amp has the current to do it....Ralph, I generally agree with your posts most of the time but I'm afraid that I have objections to this statement of yours.
Are you saying that people who have electrostatic or ribbon or planar speakers where the load impedance dips below 2 Ohms are not enjoying quality sound & that they are merely reveling in high SPL music environments in their respective homes?????
If yes, you know that that would be a load of BS on your part!
I've been reading some amplifier specs.Ay-ya! That's the problem Mitch4t! you're wasting time reading amp specs rather than listening to music! ;-)
What happens if the speaker dips to 1 ohm or below?the answer is: depends on the amp design as Minorl (& maybe some others) wrote.
The power amp is made to a certain price point so it has a certain power supply design that can support X amperes of output current. The manuf generally ensures that the output transistors do not leave the SOA (Safe Area of Operation) otherwise you are SOL! So, in such a case, when the load impedance dips below 2 Ohms, the power amp will run out of load current to supply the speaker to generate the SPL that set by your volume control. This means that the peaks of the music signal waveform will clip. This clipping is distortion (usually odd order harmonics) hence the amp will begin to sound harsh/brittle/piercing such that your mind will want you to turn down the volume. This clipping is not likely to damage your speaker 'cuz the amp is outputting a fixed amplitude at a certain non-zero frequency for (almost 100% of the time) a short duration of time. Short duration 'cuz it's the music signal & not some DC voltage. However, operating a semiconductor device at its extreme limit of safe operation is not good for the device; it can do some irreversible damage. Maybe not during the 1st or 2nd time but certainly as the number of such incidents recur because the clipping is fatiguing the device & it will finally give in.
In another case, if you attach an anemic power amp to a load that dips below 2 Ohms (an anemic amp would be an amp that, altho' specified to 2 Ohms, does not have a robust power supply i.e. high wattage output but ability to supply very little load current. Take an example: 500VA transformer with dual/two secondary voltages of 65VAC. Such a transformer can supply a grand total of 7.7A. Since there are 2 secondaries, each secondary can have 3.85A. If you calc the wattage of this amplifier you get 528W/ch into 8 Ohms. And, you look at this & go "wow! nice powerful amp!" Not! if you dig deeper - ~4A into a load that can dip below 2 Ohms is not a whole lot). Since this is not a high current amp, the heat sinks are likely to be puny. If you attach this to a load that dips below 2 Ohms & you start asking the amp to source current into this load, the output transistors will get very hot (as they'll be operating close to the upper limit of their SOA) & since the heat sinks cannot handle/dissipate the heat generated quickly, the output devices will likely explode/pop/destroy themselves & create a mess like Hifimaniac wrote.
Still another thing that could happen is that when the power amp is operating at its upper limit, the parasitic capacitances in the output devices could interact with the parasitic capacitances of the speaker cables + the speaker x-over & present an excessive capacitative load to the amplifier & the amplifier could go unstable & oscillate. This will manifest itself as harsh/brittle sound. Amps that are attached to electrostatic speakers often suffer this fate 'cuz the electrostatic speaker looks like a large/massive capacitor to the amplifier that it/amp might not have been designed to handle. Hence you find the likes of Innersound & Sanders Sound Systems offer their own power amps that match their speakers.
I'm sure that there are other ill-effects but these come to mind immediately. FWIW.