• Parallel and series connections: description and calculations

    Parallel connection

    Parallel connection is the most common connection for loudspeakers, particularly if they are portable (connecting a loop-through cable will always enable a parallel connection).

    The illustration below shows the parallel connection of a group of speakers:

    Z1 represents the first load and Zn the last (nth) load in a group of n speakers. The suspension points indicate that the connection can be made with any number of boxes. The voltage reaching each speaker is the same.
    The calculation of the total impedance in the parallel connection is given by
    1 1 1 1 1
    ---- = --- + --- + --- ... + ---
    Ztotal Z1 Z2 Z3 Zn

    For example, if we had two 8-ohm impedances and two 4-ohm impedances we would have: that 1/Ztotal = 1/8+1/8+1/4+1/4 = 1/8+1/8+2/8+2/8= 6/8 and, therefore, turning the expression upside down Ztotal = 8/6, i.e. 1.25 ohms.

    When all the elements have the same impedance, the formula becomes much simpler, being simply the impedance of the individual speaker divided by the number of speakers:

    Ztotal = ---

    For example, if we had four 8-ohm speakers connected in parallel, the total impedance would be 2 Ohms (8/4=2). Following this example, the amplifier would deliver its power per specified channel at 2 ohms, which would be equally distributed to each speaker. For example, if the amplifier specifies 1000W per channel at 2 ohms, each of the four components receives 250W. The power distribution is equal since all the elements in parallel have the same impedance.
    NOTE: It is not common to connect speakers of different impedances in parallel because it is difficult to match the power each element receives to its power rating. For example, if we were to connect an 8 ohm speaker in parallel with a 4 ohm speaker, the 4 ohm speaker would receive twice the power of the 8 ohm speaker and therefore should have twice the power rating, so that the power levels would match.