For all you electrical experts out there, help me clarify a question I have regard Ohms and speaker loads.

I read this statement when reading about speakers recently.

"When the electricity passes into the speaker, some of it is 'resisted.' The ohms rating of the speaker is how much is resisted, and an indication of how much energy it takes to drive it - the higher the ohms rating, the more difficult it is to drive."

For some reason I was thinking the LOWER the Ohm rating the more difficult a speaker is to drive (i.e a 4 Ohm speaker is more difficult to drive than an 8 Ohm speaker.....2 Ohms more difficult than 4 etc..) I thought this was the reason so many amps are rated for a load 4 ohms and above. I've never seen a warning for driving a speaker rated for greater than 8 Ohms. So I assumed the higher the number, the less resistance. Sort of an inverse relationship. I also recognize that the rating on a speaker is more like an average....it can be higher or lower depending on the frequency. Thanks for your input.

The description is not accurate. They should have said that more voltage is required for a higher impedance to achieve a given wattage. It is not necessairly "harder" to drive a lower impedance speaker - it's more a matter of the amplifier being designed to handle very low impedances such as 2 to 4 ohms.

The less the resistance the higher the current the speaker draws

an ohm is a measure of resistance, so naturally a higher number would indicate more resistance...

"It is not necessairly "harder" to drive a lower impedance speaker - it's more a matter of the amplifier being designed to handle very low impedances such as 2 to 4 ohms."-SH (ill leave the misspelling in for what its worth... hate to agree with you so soon after the last times.)

soundhound had a stereo magazine behind his spelling book in school!

"It is not necessairly "harder" to drive a lower impedance speaker - it's more a matter of the amplifier being designed to handle very low impedances such as 2 to 4 ohms"

Thanks guys. One more question. Why do most amplifier manufacturers warn only against using their amps on loads less than 4 ohms? Why would they not also warn against using the amp at higher impedances like 16 ohms or more? Obviously, there are not very many 16 ohm home speakers available (if any), but there are also few speakers rated for 2 ohms and less, so why the warning? Wouldn't a higher impedance (16 vs. 4) be more potentially damaging to an amp?
16 ohm loads might be possible if drivers were wired in certain configurations. Example: A subwoofer cabinet with two 8 ohm woofers. If you had a mono amplifier that was not rated for loads under 4 ohms, you might wire the woofers in series to achieve a 16 (approx.) ohm load. Probably a bad example, but just trying to better understand.

Thanks,
Steve

Consider that the lower the impedance the closer you are getting to a short which would be 0 ohms. Audio amps need something to work against and low impedance can let them "overwork" them selves causing excessive heat, distortion and other nasties. If the amp can run at 0 ohms it's a welder

Thanks Keta, that analogy makes perfect sense. For some reason, I think my 755 would make a pretty good welder...but I'm not willing to try!

i caught this in a description of b&w speakers,just somebody elses opinion i guess


Sensitivity combined with impedance indicates how much amplifier power is required for the loudspeaker to play at satisfying volume levels. When comparing this spec to low impedance (4 ohm) designs, you must add 3 dB to the figure, since 4 ohm loads draw twice the current from the amplifier, providing the illusion of greater sensitivity, while placing more stress on the amplifier?s power supply. The moderate sensitivity of the Pearl indicates that small amplifiers can achieve realistic levels in all but the largest rooms.

System impedance indicates whether the speaker presents a "hard" or "easy" load on the amplifier. True 8ohm speakers are less amplifier and cable sensitive, and partner well with a broader range of amplifiers, including tube designs.

Today's home theater amplifiers are nowhere as robust as the stereo amplifiers of 20 years ago - the presence of the "6 ohm" switch is a result of this. A good stereo amplifier of that period would have no problem whatsoever driving a 4 ohm load all day long. "Hard" and "Easy" are relative terms - 4 ohms is hard for most home thater amps, but easy for a more robust one, depending on how they're designed.