Topic: those good with musical equipment...what the difference 4ohm vs. 8 ohm ..

[Cactus]

hey now,

im looking at upgrading my bass amp and also purchasing a pa .. so as ive been digging around ive come across these 2 options.. im familar with the term ohm but no clear as to its affects regarding musical equipment.. so which are the benefits and or drawbackd of each.. thanks in advance

cactus

[F.O.Bean]

8ohm is technically only allowing so much power thru, ohms are resistance to the signal, so that would mean 4-ohm stuff lets more power thru because there is LESS resistance, thus creating more power/etc

the 8-ohm stuff has MORE resistance and thus lets less power thru

[jpschust]

http://www.bcae1.com/ohmslaw.htm

[Cooker]

ohms are the measurement for impedance. in the context of a bass cabinet, some speakers are 8 ohm, some are 4 ohm.  amps typically output 4ohms bridged mono /  8 ohms x2. so if your amp is rated at 100 watts per channel at 8 ohms, it will actually output 200 watts per channel at 4 ohms. but it will run hot. and dirty - distortion will probably be higher. 

as to what to get - well you can often get a little higher bang for your buck with 4 ohms.

[Cactus]

very cool,

yea ive been digging a bit around on talkbass and they always seem to get pretty complex with there responses. i guess i was most curious if either affected the sound in any way. i also understand power doesnt necessarily mean volume..after reading i realized if i plan on adding a 2nd cab down the road 8 ohms would be better as very few amps go below 4 thus 2 4ohms cabs wouldnt work.

thanks again 

for those interested im toying with ampegs cheaper line..not sure if anyone else plays but my little 210sp isnt doing the trick anymore..so im thinking of either a 210 and 15 or just 410 .. 

[pfife]

as to what to get - well you can often get a little higher bang for your buck with 4 ohms.

This is what I've always heard too.

[BobW]

Don't piggyback 4 ohm cabinets, you'll get 2 ohms (few amps work with 2 ohms, and some will self-destruct)
If you piggyback two 8 ohm cabinets, you get 4 ohms, which is fine if your amp is rated for it.

I've always felt safer with 8 ohm stuff and lean toward it when most else is equal.
The reason is that impedance ("ohmage") is not constant in a speaker. At some frequencies, in some placements an 8 ohm speaker can be under 5 ohms, a 4 ohm speaker can go below 2. So piggybacked 4 ohm speakers can actually approach under 1 ohm, depending on placement and frequency. It takes an amazing amp to handle that sort of load.

Hope that helps.

[morst]

http://www.bcae1.com/ohmslaw.htm

that's a cool site, but they have the metaphor backwards.

The resistance in the faucet corresponds to the amount that the valve is open

actually, conductance would correspond to how OPEN the valve is, Resistance matches with how much it's closed (inverse functions)

a 4-ohm speaker will draw more power and more heat from an amp to produce the same sound pressure.  This is typically because a 4ohm speaker has less wraps of windings for it's speaker "motor".  The 8-ohm drivers will be more efficient, and produce as much air movement as a comparable 4ohm driver with half the power reqiurement.  If you are going to be at risk of popping circuit breakers due to overload, the 8-ohm speaker will reduce the likelihood of this  occurring.

Also- as others said, connecting speakers in parallel causes the impedence to drop, so that two 8-ohm cabinets would have the same effective impedence as one 4-ohm one.

please note- resistance and impedence are identical in DC circuits, but impedence varies according to frequency in AC circuits.  Both are measured in Ohms, but for speakers, Impedence is the meaningful value.