How to calculate resistance in parallel

It is often that we have to calculate resistance in parallel, since in audio we are plugging in guitar cabs, speaker cabs, etc. Most often, simply daisy chaining one speaker next to the other will result in a parallel connection. First off, what is a parallel connection?

A parallel electrical connection is simply when two loads (e.g. speakers) are connected to the source in the same manner, such as positive to positive, and negative to negative.

The actual formula is: 1/R1 + 1/R2 + 1/R3 + ... = 1/Rtotal

This means 1 over first load, plus 1 over second load, etc.

EXAMPLE 1: 2 8 ohm cabinets

To solve, this would be written 1/8ohms + 1/8ohms = 2/8ohms. Now to solve for Rtotal, then flip the number to 8/2, or 4 ohms.

EXAMPLE 2: How about 3 8ohm cabs? 1/8 + 1/8 + 1/8 = 3/8, solve for t, equals 2.667.

EXAMPLE 3: How about 2 8ohm and 1 4ohm? A little more tricky...
1/8 + 1/8 + 2/8 = 4/8, flip it and you have 2ohms (which will most likely melt your amp!)

As a related question, the power consumption (watts) is a straight sum of the collective cabinets.

Now you know the correct formula for calculating resistance in parallel!

For additional reading, please check out the related article:
How to calculate resistance in series