Ohms?

bravo, rayhall! yours is an exceptionally literate and erudite answer to a seemingly simple question.

Here's my two cents. In order for electric current to flow it must be drawn by a load, which is like a hungry energy magnet. The resistance in Ohms is a measure of the load/hunger. The higher the resistance in Ohms the less energy flows. Conversely, as the resistance of the load drops, the magnet gets bigger, hungrier for more energy. Good amps can accomodate these load variations and spill more juice into the load. But as the resistance of the load approaches zero the amp goes nuts trying to fill the void and hopefully overheats and shuts down. Any speaker's ability to convert this energy into sound at a given frequency varies, so I wouldn't say offhand that the rating in Ohms will give you much of a clue as to efficiency. The rating does point towards the adequacy of the amp you'll require to feed it. The bottom line is that amp designers and speaker makers have to work from some kind of starting point to get these components to work together, which for some reason has a baseline of 8 ohms. Is it arbitrary? It's probably just a freak of nature stemming from the measurement of early design efforts that later became an agreed upon average design target.

Be careful! Speaker impedance and efficiency are two very different things. If a speaker is 8 ohms, all that means is that the speaker's voice coil has a nominal impedance of 8 ohms (Rayhall gave an excellent explanation of impedance). The efficiency is the measure of the speaker's ability to turn electrical energy in sound waves. This is represented in db (sound wave intensity) per watt (electrical energy). The higher the rating ie. 93 db/watt, the better the speaker is in converting electrical energy into sound waves. For example a speaker rated at 93 db/watt is more efficient than one rated at 89 db/watt and their impedances can both be 8 ohms nominal.

Great Question !!! My speakers have Sensitivity 90dB spl; Nominal Impedance 8 Ohm; Minimum 3.5 Ohm. The bass is on the light side (I use a REL sub) and very very slightly slower compared with the rest of the speaker. Is this reflected in the 3.5 minimum Ohms?? I've read an amplifier with a lower output impedence the better to drive the bass better. Is this true? Comments??

Simplified answer for the non-technical: As consumer stereo evolved, speakers manufacturers provided an "ohm" (electrical resistance) rating, so that consumers could match a speaker with their particular amplifier. This way done many, many years ago, before transistor amplifiers were even produced! Now what does that "ohm" rating mean to today's consumer , not really that much (unless he buys some exotic, old fashoned tube amp design of yore). If a speaker is rated at four ohms vs eight ohms, your amplifier may be able to produce more clean power into the lower ohm rated speaker, but this is a general statement at best. To reiterate: Unless you have some sort of exotic tube amplifier; this specification will not help you determine if one speaker is superior versus another. Four ohm speakers don't necessarily sound better than eight ohm speakers and visa versa.