Charles1dad, take a look at this article, it will help in understanding my explanation that follows:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.phpFour ohms came in with the transistor- we all know that. However, along with the transistor came the new Voltage design rule. The rule has been in place since the mid 1970s. IMO the rule has its problems and one of them is this: with it has come the idea that if you parallel two speakers, the efficiency increases.
Now, if that were really the case, it would violate some pretty fundamental rules of physics- and clearly falls into the same area as perpetual motion machines. That is to say, you don't get that increased energy for nothing. What is really happening is that there is confusion between the idea of Efficiency (how much power it takes to drive a speaker) and Senstivity (which is sort of the Voltage rule equivalent, IOW how much voltage a speaker has applied to it for a certain amount of output).
Now into an 8 ohm load the two are the same. For example if you have 1 watt into 8 ohms the voltage is 2.83 volts. But if you apply 2.83 volts to a *4* ohm load you will have 2 watts in the load. People tend to use the two words interchangeably and that is where the confusion lies. Power (1 watt/1 meter) is the older Power Paradigm spec and Voltage (2.83V/1 meter) is the Voltage Paradigm spec.
Now tubes have always been kind of expensive to make power. So to deal with that, in the old days high efficiency speakers tended to be more common, as was 16 ohms. When transistors came in, one thing that was not lost on the industry was the fact that you could build a transistor amp that made the same power as a tube amp, charge about 90% of the tube amp price, but have about 10-50% of the cost of building the tube amp. IOW follow the dollars.
Now this was not lost on the speaker manufacturers. When it was seen that you could double the power of some transistor amps simply by cutting the impedance in half, some speaker manufacturers began making 4 ohm speakers to get that extra output from the amp. You see, building high efficiency speakers is expensive because you have to have precision voice coil gaps to get the efficiency. By going to reduced precision by increasing the voice coil gap, the cost of the speaker went down. But if you went to 4 ohms you got 3 db of Sensitivity "back". Again, for such speakers the industry found that they could charge slightly less than the high efficiency models, but the cost again was dramatically reduced- they made more money.
I think it would be great if this was simply my opinion (one would like to think that the changes we see in audio have to do with increased fidelity rather than just making more bucks) but you don't have to look very far to see that this is what went on. I can name plenty of examples beyond these two and I am sure others can too.
So- if we turn our backs on the money-making schemes and focus instead on how to make the equipment sound better, right away higher impedance in the speakers emerges as a simple solution.
