Extension cabinets and ohms math

[RVA]

So here is the scenario:

Head has 2 outputs - "Main" and "Extension"

Head has a selector knob where you can choose the 4/8/16 ohms

What is the appropriate ohms selection if you connect a single 8 ohm speaker to 1 output and a 16 ohm cab to the other (2x12 @ 8ohms each in series)?

Thanks for any help

 

[DonP]

If you want the parallel sum of A and B, it is (A x B)/(A + B). So an 8 and a 16 make 5.333

 

[jtcnj]

does the amp documentation describe how the switch should be used?

If the output jacks are simply in parallel like old Fender, then I would think you would pick whatever is closest to the 2 cabs in parallel.
8 x 16/(8+16) = 5.333, so I would pick 4Ω.
EDIT Don posted while i was typing

 

[RVA]

If you want the parallel sum of A and B, it is (A x B)/(A + B). So an 8 and a 16 make 5.333

does the amp documentation describe how the switch should be used?

If the output jacks are simply in parallel like old Fender, then I would think you would pick whatever is closest to the 2 cabs in parallel.
8 x 16/(8+16) = 5.333, so I would pick 4Ω.
EDIT Don posted while i was typing

The outputs run in parallel, so chose 4 ohm setting when both plugged in - thanks!

 

[eSGEe]

ohm.....................ohm..............ohm.......bop bop a reebop

 

[Dave Sloven]

I wouldn't used mixed ohms cabs. It gives you an odd total load but more concerning is that more of the power flows to the lower resistance cab

In other words it's the 112 that will be doing all the heavy lifting

 

[Don O]

I wouldn't used mixed ohms cabs. It gives you an odd total load but more concerning is that more of the power flows to the lower resistance cab

In other words it's the 112 that will be doing all the heavy lifting

Agree, electrons take the path of least resistance. It’s the law

 

[Tony M.]

If you tie a knot in the cable to the lower resistance cabinet the tight turns will
slow the electrons down thereby evening out the power flow to the speakers.

 

[jtcnj]

If you tie a knot in the cable to the lower resistance cabinet the tight turns will
slow the electrons down thereby evening out the power flow to the speakers.

but you have to calculate how many knots you tie to make an effective induction coil.
Maths get in the way of my rawk.

 

[guitarweasel]

 

[Inspector #20]

but you have to calculate how many knots you tie to make an effective induction coil.
Maths get in the way of my rawk.

How about a clothespin? Works on a dick...

 

[Tony M.]

 

[eSGEe]

ugh math

 

[Sp8ctre]

I wouldn't used mixed ohms cabs. It gives you an odd total load but more concerning is that more of the power flows to the lower resistance cab

In other words it's the 112 that will be doing all the heavy lifting

It's not so much how much load that's going to the speakers you have to worry about. It's how much strain you're putting on the amp if your output impedance is wrong. With a 5.33 ohm total load use the 4 ohm setting and the amp and speakers will be just fine. The speakers are more likely to be damaged by your power output going to high for their rating...

 

[Mitch Pearrow SJMP]

If you tie a knot in the cable to the lower resistance cabinet the tight turns will
slow the electrons down thereby evening out the power flow to the speakers.