Ohm load on cabinets

[Jamie R]

This may have been discussed before, so, I apologize if I’m being redundant. My question is: what should I set my amps switch at? 4, 8, or 16 ohms? I have an 8 ohm 1x12 cab and a 16 ohm 1x12 cab and I’d like to run both off of my head. Y’all are some of the smartest people in this world. I believe y’all can help me.

thanks in advance!

 

[RallyFanatic]

4ohms, and you’ll be pushing the 8ohm cab harder, so it’ll be louder. Replacing the 8ohm speaker with a 16 ohm speaker (and setting the amp at 8 ohms) would be infinitely better and less stressful for the amp.

 

[Jamie R]

4ohms, and you’ll be pushing the 8ohm cab harder, so it’ll be louder. Replacing the 8ohm speaker with a 16 ohm speaker (and setting the amp at 8 ohms) would be infinitely better and less stressful for the amp.

If I set the amp at 16 ohms, would I keep my amp safe while using my cabs without destroying them or the amp?

 

[andy474x]

Any time you combine speaker cabinets (if you’re running them from dual jacks on the back of your amp) you are running the cabs in a parallel circuit. You should calculate the total load using Ohm’s Law for parallel circuits, in this case 1/(1/R1 + 1/R2) = total ohm load, R1 and R2 being the ohm rating of each cabinet. In this case, 1/(1/16 +1/8), breaking down to about 5.3 ohms. You would probably be fine running the amp at 4 or 8 ohms, really.

 

[RallyFanatic]

Any time you combine speaker cabinets (if you’re running them from dual jacks on the back of your amp) you are running the cabs in a parallel circuit. You should calculate the total load using Ohm’s Law for parallel circuits, in this case 1/(1/R1 + 1/R2) = total ohm load, R1 and R2 being the ohm rating of each cabinet. In this case, 1/(1/16 +1/8), breaking down to about 5.3 ohms. You would probably be fine running the amp at 4 or 8 ohms, really.

this!

 

[vchizzle]

I wouldn't do it. Best to replace one of the speakers so they match. In general, 2 16 ohm cabs, set to 8, 2 8 ohm cabs, set to 4.

 

[markd21]

Old Fenders only run at 4 ohms (except 4 speaker combos, they run at 2 ohms) and before I could afford properly rated, matching cabs (2×8 ohm or 2×16 ohm) I would mix match whatever I had. It would work for awhile, but always ended up creating a problem. Just pick one cab and live with it until you can do it right.

 

[shinksma]

I wouldn't do it. Best to replace one of the speakers so they match. In general, 2 16 ohm cabs, set to 8, 2 8 ohm cabs, set to 4.

Mathematically, it doesn't need to match - the amp won't care, it will just see a combined load of roughly 5.3 ohms, as calculated by @andy474x .

Imagine, if you will, that the 8 ohm cabinet really has two 16 ohm speakers wired in parallel inside, resulting in a net 8 ohm impedance. By then also connecting the 16 ohm 1x12 cab in parallel, the amp "sees" three speakers in parallel, all 16 ohm, or 5.3 ohms net. The safest setting for the amp would be the 4 ohm setting. (I actually asked PRS about this very situation, adding a 2x12 cab at 8 ohms to an existing 1x12 combo with 16 ohm speaker.)

In the case of the OP, mixing an 8 ohm speaker with a 16 ohm speaker, the speakers will naturally behave a bit differently in the two cabinets due to their different impedances, but maybe that will result in a more desirable tone, overall.

However, me being the "optimize if possible" type, would prefer to use speakers all of the same impedance individually, wired in parallel, such that the amp sees "exactly" 4 or 8 or 16 ohms. (I realize the speakers are never truly exactly a certain impedance, it will vary by frequency and probably a few other minor factors).

 

[Kiwi]

Easy to remember stuff, for the liberal arts majors like me:

1) (Cab 1 x Cab 2) divided by (Cab 1 + Cab 2) so you get: (16x8)/(16+8) or 128/24 = 5.3 ohms

2) Sloppier but better than none: Add the ohmages and divide by 4. So you get: 16 + 8 = 24, divide by 4 = 6 ohms.

3) Use the lower ohm setting on your amp. Your amp wants to see more resistance, not less. Set it at 4 ohms.

=K

 

[Alnus Rubra]

Good information sharing guys. Nice one.

 

[Jamie R]

You folks rock! I knew I could find the answers here. Thanks for all the input!!