Ohms?

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.

Great thread and great explanations. However, ohm's are important even with modern solid state equipment and it's not so much to do with exotic tube equipment. Not nominal imedance, but IMEDANCE CURVES. In the real world, this is what drives amps (yes, solid state amps) nuts. I've been on the planar/ribbon/electrostatic road for quite a few years and what makes amp matching so critical for these puppies is the impedance swing (impedance minima at high frequencies combined with higher impedance in low frequecies). Lots of people fret impedance dips but this isn't such a big deal since these occur at high frequencies and there isn't a lot of energy going on there. It's how an amp responds to the dips combined with what goes on in the lower mids that really counts. The Newforms have a curve of 2ohms to 100ohms, I think. If you were an amp tring to play dynamic music with lots of fast changes in impendance you would be working your proverbial ass off to keep up with a curve like this. My speakers (CLS's) are tame by comparison... 1.5 ohms to 35 ohms in the mids. (One version of my speakers dropped down to .6 ohms!) Most speakers rated at a nominal 8ohms have far less swing -- usually less than 6ohms in either direction -- making the amp's job easier. The type of music (degree of dynamics and low frequency extension) also makes a big difference in an amp's ability to keep up with the swing. Again, great explanations of terminology that's thrown around and not fully understood in real world applications. Thanks for bringing it up.