5150 Newb Questions....ohmage....

[trey85stang]

i see some confusion in this thread... ill throw in my two cents.

First the OP, if I understand your post you have a steree 4x12, which can run in either 4/16ohms in mono or 8ohms per side in stereo. Your friend tell you to run from the 8ohm outs of your 5150 into the stereo 8 ohm inputs. That will cause an ohms mismatch as those two 8 ohm jacks are parallel. which will half both your 8 ohm inputs to a 4ohm load which is very bad.

high wattage tube amps (99%) cannot accept ohm mismatchs (up or down) without causing damage. You might be safe for a few minutes but your amp is going to lose mojo in the form of smoke eventually if play it too long that way.

Solidstate amps can generally accept higher loads then their optimal rating, but it will cost power. Generally assume if the amp wants a 4 ohm load, an 8 ohm load will half your power, and a 16 ohm load will cut 3/4 of the power. These is just a slight generalization as ever amp is different you can find the actual power dfferences in the manual generally.

and i just read the post above me.. which is pretty much spot on to what I just said

 

[trey85stang]

I personally have to turn my amp up another 25% when connecting an 8ohm cab instead of my 4 ohm. I understand what you are saying by perception, but a 25% loss in volume is more than perception to me.

Try connecting an 8ohm Mesa and a 16ohm Krank together and the Krank is definately quieter. Almost cant tell if its playing when to cabs are next to eachother.

Same with a 4ohm Marshall and a 8ohm Mesa.

Now if you simply flip the ohm switch on the head with the same cab, there is not much difference in volume. But 2 different cabs with the same head is clear.

If you search the net you will find everyone saying the same thing.

Example from someone who asked the same question about ohms and volume on yahoo:

So, in a nutshell, if your amp's output load impedance is rated for 8-ohms, and you put a 16-ohm speaker on it, you will essentially get half the normal volume of the amp, whereas putting a 4-ohm speaker on it, will result in twice the volume.

Its strange that you have a Krank Cab and a Marshall Cab and dont see the difference.

Plug the two in for a minute with the head on 4ohms and the Marshall in the 4ohm jack and connect the Krank cab and tell me its not hard to hear the Krank......

you're forgetting the speaker aspect, speakers have different decimal ratings.. a v30 is rated at 100db, yet a krank cab which most likely has texas heats which are rated at 99db, g12t-75's are rated at 97 etc.. etc..

 

[ochants76]

^^^^good point!!!!!

I have vintage 30s in both my krank and marshall cabs. Just different ohms...