The most common methods to wire up speakers are Series and Parallel.
It is also quite common to wire Speakers in a Series/Parallel Combination.
Single speaker
Wiring up Speakers correctly to provide the best possible sound, requires some knowledge of Loading, Phase, and Impedance, while understanding Ohms Law will help you to connect your speakers properly.
SERIES
Adding Speakers in series increases the overall resistance of the circuit.
Therefore the resistance of each Speaker is added together, For advanced installations with Multiple Speakers, Series Speaker wiring can be used to increase the resistance of the “equivalent” or “overall” resistance that the Amplifier sees. This allows the Amplifier to run cooler and more efficiently.
Series Circuits are “voltage dividers”, and using Ohms Law, one sees the result as a decrease in amplified voltage audio signal to each Speaker. Since Series Circuits are “voltage dividers” each Speaker sees a percentage of the amplified output from the Amplifier. It is often assumed the Amplifier is producing less output, but it still produces the same output, because each Speaker only gets a percentage of the overall power.
Formula: Znet = Z1 + Z2 + Z3 + .... + Zn
Example:
2 x 4 Ohm Speaker = 4 + 4 = 8 Ohm Load
2 x 8 Ohm Speaker = 8 + 8 = 16 Ohm Load
PARALLEL
Adding Speakers in parallel decreases the overall resistance of the circuit
Parallel Speaker Wiring combines all Speakers (+) positive Speaker leads together, and all (-) negative Speaker leads together.
Adding additional Speakers is as easy, however, adding Speakers in Parallel causes the overall resistance of the circuit to drop, as resistance drops, the current must increase according to Ohms Law. So, each time a Speaker with the same resistance is added to the parallel circuit, the current draw on the amp increases. The circuitry of the amp must be able to handle this increase in current at the reduced resistance.
Formula: Znet = 1 / (1/Z1 + 1/Z2 + ... + 1/Zn)
Example:
2 X 4 Ohm Speaker = 1 / (1/4 + 1/4 ) = 2 Ohm Load
2 x 8 Ohm Speaker = 1 / (1/8 + 1/8 ) = 4 Ohm Load
Note: If more than 2 Speakers are connected in Parallel, so long as they are all the same impedance then the net impedance of the load is equal to the impedance of the one Speaker divided by the total number of Speakers. For Example 3 8 Ohm Speakers in Parallel, the Impedance is 8/3 or 2.667 Ohms.
A COMBINATION OF SERIES & PARALLEL
In reality this is just two sets of Series Speakers wired in Parallel
Formula: Znet = Znet1 + Znet2 + ... + Znetn; where Zneti = 1 / (1/Z1 + 1/Z2 + ... + 1/Zn)
Example:
4 X 8 Ohm Speaker = [1 / (1/8 + 1/8 )] + [1 / (1/8 + 1/8 )] = 4 + 4 = 8 Ohm Load
WIRING A FULL STACK
The amp usually has two speaker outputs (one for each cab)
The output jacks are wired in parallel. It means Znet = 1 / (1/Z1 + 1/Z2 + ... + 1/Zn)
Therefore having 2 cabs at 8Ohm the head will see 1 / (1/8 + 1/8 ) = 4 Ohm Load
Enjoy!
