How to calculate the net impedance when multiple speakers are connected in parallel.
If you can do some basic math it is very easy to figure out impedance loads of multiple speakers across one amp. To calculate parallel impedances use the following formula.
1
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1/R1 + 1/R2 + 1/R3, etc.
Where R1, R2, etc. are the impedance values of each speaker that will be in parallel. You can have as many as you want and the math will always work out.
You may have to refer back to your old textbooks on how to add fractions (remember, you need a common denominator), but doing the math you can see that three 8-ohm speakers connected in parallel make a net load of 2 & 2/3 ohms (or 2.66666…). Two 8-ohm speakers in parallel make a net load of 4 ohms. An easy shortcut is to remember that any two like impedances in parallel make a net load of half of what they individually are. So two 16-ohm speakers in parallel make an 8-ohm load.