Simple Calculation for Speakers in Parallel
If all the speakers in parallel have the same impedance, then the calculation is easy. Simply divide the impedance by the number of speakers in parallel.
Example 1: Four 8 ohm speakers in parallel: 8 divided by 4 = 2 ohms.
Example 2: Two 4 ohms speakers in parallel: 4 divided by 2 = 2 ohms.
Not so Simple Calculations for Speakers in Parallel
For calculations involving speakers in parallel with different impedance, the following formula is required (it can be used with speakers of similar impedances too).
If you have a calculator with 1/x button then this calculation is not too difficult. If you don’t have that function on your calculator, or if you don’t like formulas, check out the calculators below.
Calculator for Speakers in Parallel
Below is my new calculator for 2, 3 or 4 speakers wired in parallel.
Simply type the impedance of each speaker into the white boxes (or use the drop-down values). Use N/A for unused speakers in this calculator. The total impedance will be calculated for the entered speakers.
Also for each speaker is a calculated percentage. The shows how the power output of the amplifier is shared between the speakers. Power sharing is a consideration when using speakers with different impedance. See How Multiple Speakers Share Power for further details.
The final calculation is labelled “Power Differential”. This calculates in dB (decibels) the power level difference between the highest and lowest power as it is shared across the speakers in parallel. This shows the power level difference when using speakers with different impedance.
This calculator will help you understand the total speaker load on your HiFi amplifier. For a better understanding of this and what to do about it, read the articles How do I Connect Multiple Speakers to my HiFi Amplifier and How to wire four HiFi speakers or How to connect 2 speakers to one amplifier or watch the video in the article Understanding Speaker Impedance.
Note: all these calculations are for connecting manufactured speakers (boxes). They are not used when building your own speaker boxes and connecting multiple speakers in a cabinet using a crossover circuit. A crossover splits the signal into different frequencies for each of the speakers and makes the total impedance calculation complex (as impedance is frequency dependent). That is why speaker designers get the big money, and as installers we benefit from their expertise.
If you need further advice on connecting speakers in parallel, please read the FAQs before submitting your question. You also find an answer in the comments below.