Can someone please explain this to me in English? If a speaker is rated at 86db compared to another one at 92db which one puts more strain on the amp? Does more strain mean using more electricity hence costing me more to run the darn thing? Same thing with ohms. Does it take more power (hence more dinero) to run a 4ohm speaker comapered to an 8ohm speaker? Sorry to sound ignorant. Thanks guys.
It would take 4 times as many watts to drive a speaker with a sensitivity of 86dB than it would one with 92dB. You have to double the watts to get a 3dB increase in volume.
A sensitivity rating of 86dB means the volume level is 86dB if you're standing a meter away from the speaker and if you're providing one watt of power to the speaker.
The lower the resistance to your speaker, the more power that is applied to it (power = voltage^2/resistance). However, the amount of current will also increase. When going from an 8 ohm speaker to a 4 ohm speaker, the current will double. If your amp can't handle that, it will overheat and thus ruin the amplifier or it will go into protection mode.
Bottom line: don't use your amp with 4 ohm speakers unless your amp's instructions specify that it can handle them. Most lower-end receivers (like mine) can only handle 8 ohm.