ohms sweet ohms... (1 Viewer)

[righteous harmony]

ok... can somebody please explain impedance in reasonably simple terms (in relation to amplifiers and speakers)? it's been explained to me several times before but i tend to glaze over when numbers are involved. cheers...

 

[the departed]

OHMy god.

 

[Daniel]

ok... can somebody please explain impedance in reasonably simple terms (in relation to amplifiers and speakers)? it's been explained to me several times before but i tend to glaze over when numbers are involved. cheers...

This is constantly wrecking my head as well.
Don't know the full jist about it but if i am using my valve head with two 16ohm cabs i am to set the head to 8ohm. Apparently mixing cabs with different ohms is not too advisable ( with valve heads anyway).

 

[brianoak]

If the impedance on the two cabs you are running is 16 ohms you should set your head to 8ohms and it will push it fine.

Ideally the impedance between heads and cabs should always match.You can run a 16 ohm cab with your head set to 8 but you will lose volume.

If all you remember is to match them you should be fine.

 

[sparse]

Do you know, do you lose much volume? I have a 100w bassman at 4ohms that I run into an 8ohm cab, but to get any use out of it I'm running it at a volume of 8. Now it is a Fender but a Marshall of similar loudness only needs to be at about 3. Is it an ohm+fender problem?

 

[egg_]

Ohms is how much resistance there is to the signal coming from your amp. The "ohms" rating on your head is the LOWEST resistance your head is designed to handle - running it with a speaker load that adds up to less than this can damage your speakers or your amplifier. If you run the head with a higher load than the minimum (say one 8 ohm cab on a head that's rated 100W at 4 ohms) you will get less power out of the head and therefore and less volume

2X16 ohm cabs = 8 ohms
2x8 ohm cabs = 4 ohms
2X4 ohm cabs = 2 ohms

1x16 ohm cab + 1x8 ohm cab = 5 and 1/3 ohms
1x8 ohm cab + 1x4 ohm cab = 2 and 1/3 ohms
1x16 ohm cab + 1x4 ohm cab = 3.2 ohms

 

[Space]

Anyone know roughly how much less volume you'd get running a 4 ohm head(probably 300watt) into an 8 ohm cab?

 

[Umfufu]

Anyone know roughly how much less volume you'd get running a 4 ohm head(probably 300watt) into an 8 ohm cab?

Not sure, but if you add a 2nd 8 Ohm cab you'll bring the impedance down to 4 Ohms.

 

[steveamanakick]

Not sure, but if you add a 2nd 8 Ohm cab you'll bring the impedance down to 4 Ohms.

Can i use a 8ohm min load amp with a 4ohm cab? Will it fuck it up? The cab has 2x12 4ohm speakers with one input

 

[Space]

Not sure, but if you add a 2nd 8 Ohm cab you'll bring the impedance down to 4 Ohms.

I know this much already. Wanna buy me a second 8 ohm cab?

 

[Space]

Can i use a 8ohm min load amp with a 4ohm cab? Will it fuck it up? The cab has 2x12 4ohm speakers with one input

Ohms is how much resistance there is to the signal coming from your amp. The "ohms" rating on your head is the LOWEST resistance your head is designed to handle - running it with a speaker load that adds up to less than this can damage your speakers or your amplifier.

That answer it?

 

[Umfufu]

I know this much already. Wanna buy me a second 8 ohm cab?

Yeah, sure.
Mesa Boogie ok with you?

From what I've read, the volume difference between using a 4 Ohm & 8 Ohm cab is a couple of dB, which is barely detectable by us human folk.

BUT,
I've never tried it out myself so. like I said, I'm not sure.

 

[Space]

Yeah, sure.
Mesa Boogie ok with you?

From what I've read, the volume difference between using a 4 Ohm & 8 Ohm cab is a couple of dB, which is barely detectable by us human folk.

BUT,
I've never tried it out myself so. like I said, I'm not sure.

Sound that'll do. Cab wise as long as it has eminence speakers it's good with me.

 

[ernesto]

bit of a thread resurrection with probably an easy to answer question.

recently bought a 100w valve head and the two outputs on the back are unmarked.

the 2 x 12 cab i am currently using is 16ohms and has only one input for the two (8ohm each, 50w each) speakers. and i dont want to sizzle my amp so im reluctant to keep using it.

the sound is the same no matter which output i use so im guessing theyre the same (inside they are wired together). there is no markings inside the head or selectable output switch (other than current switch for the foreign).

can i assume:
they are both 8ohms and i can rewire my cab to give each speaker its own input(theyll be technically stereo)?
then i can plug both head outputs to both cab inputs and both will be 50w and it'll be all perfect?

im going to get it serviced anyway and im sure the amp guy will tell me but i have to wait as ive not the cash for it just yet and am in the middle of scoring a cab and itd be nice to know this so i can gop ahead with the purchase from yer man.

 

[JohnnyRaz]

bit of a thread resurrection with probably an easy to answer question.

recently bought a 100w valve head and the two outputs on the back are unmarked.

the 2 x 12 cab i am currently using is 16ohms and has only one input for the two (8ohm each, 50w each) speakers. and i dont want to sizzle my amp so im reluctant to keep using it.

the sound is the same no matter which output i use so im guessing theyre the same (inside they are wired together). there is no markings inside the head or selectable output switch (other than current switch for the foreign).

can i assume:
they are both 8ohms and i can rewire my cab to give each speaker its own input(theyll be technically stereo)?
then i can plug both head outputs to both cab inputs and both will be 50w and it'll be all perfect?

im going to get it serviced anyway and im sure the amp guy will tell me but i have to wait as ive not the cash for it just yet and am in the middle of scoring a cab and itd be nice to know this so i can gop ahead with the purchase from yer man.

i think that as long as the cap/speaker impedance is greater or equal to the impedance of the transformer output you should be ok. so as long as your cab is 16ohm, you can put 16, 8, or 4ohm into it no bother. Given that any amp Ive seen is either 4/8/16ohm I'd imagine you'd be ok? can anyone confirm this??

 

[Space]

i think that as long as the cap/speaker impedance is greater or equal to the impedance of the transformer output you should be ok. so as long as your cab is 16ohm, you can put 16, 8, or 4ohm into it no bother. Given that any amp Ive seen is either 4/8/16ohm I'd imagine you'd be ok? can anyone confirm this??

I can confirm that you're a bit off the mark. When you see the switch on the back of a head saying 4/8/16 then the switch selects a different tap on the output transformer. Generally with solid state amps you're grand with say double Ohms on the cab but the amp will put out less power so 4ohm head into 8ohm cab is fine but you won't get the full power capability of the head. However with tube heads not matching the impedance can lead to blown output transformers which can be a very expensive fix. Some transformers are fine with 1:2 mismatch some are not, either way it's best to match them to be sure.

In Ernesto's case I'd say plug the head into a 16ohm cab then a 8ohm cab and see which sounds better and louder. That'd be the best indication imo but I'm not by any means an expert or overly knowledgeable on these things so can't guarantee it's completely safe to do this....

 

[ernesto]

I can confirm that you're a bit off the mark. When you see the switch on the back of a head saying 4/8/16 then the switch selects a different tap on the output transformer. Generally with solid state amps you're grand with say double Ohms on the cab but the amp will put out less power so 4ohm head into 8ohm cab is fine but you won't get the full power capability of the head. However with tube heads not matching the impedance can lead to blown output transformers which can be a very expensive fix. Some transformers are fine with 1:2 mismatch some are not, either way it's best to match them to be sure.

In Ernesto's case I'd say plug the head into a 16ohm cab then a 8ohm cab and see which sounds better and louder. That'd be the best indication imo but I'm not by any means an expert or overly knowledgeable on these things so can't guarantee it's completely safe to do this....

i was afraid you tell me those things you said. cheers Moosey. reckon ill just lob the head in to be serviced end of month and buy the cab anyway, sure if i end up having to rewire it, its not the end of the world. am i in the right ballpark with regards to using both outputs at same time for two speakers if they happened to be matched to the speakers?

 

[Space]

I'd imagine it's 8 ohm output and if they're wired together like you said you get two 16 ohm outputs in parallel which would lead me to believe that the head is fine running at either 16 or 8 ohm allowing you to use one or two 16 ohm cabs. I wouldn't go running two 8 ohm speakers in parallel (in the same cab) as you'll have the transformer seeing 4 Ohm which I doubt is a good idea here.

 

[ernesto]

I'd imagine it's 8 ohm output and if they're wired together like you said you get two 16 ohm outputs in parallel which would lead me to believe that the head is fine running at either 16 or 8 ohm allowing you to use one or two 16 ohm cabs. I wouldn't go running two 8 ohm speakers in parallel (in the same cab) as you'll have the transformer seeing 4 Ohm which I doubt is a good idea here.

when i said rewiring the cab i meant that each speaker would be independent of each other in the 2 x 12 cab and have its own input. are they only 16ohm parallel outputs when two cabs are connected?
it seems as though i could use either one or two 16ohm cabs, also, the volume was only about 1/3 up and the two 12 inch speakers were rattling like shit. id be afraid id blow them!

 

[ernesto]

when i said rewiring the cab i meant that each speaker would be independent of each other in the 2 x 12 cab and have its own input. are they only 16ohm parallel outputs when two cabs are connected?
it seems as though i could use either one or two 16ohm cabs, also, the volume was only about 1/3 up and the two 12 inch speakers were rattling like shit. id be afraid id blow them!

they would be independant of each other, ie: not 4 ohms but two 8 ohms.
in meaning that a 2x12 cab would now have a stereo input. one input per speaker. do i make any sense?