Check out Part I, Part II, and Part III of this series.

The effect that different speaker wiring options and total speaker impedance load have on your overall tone is subtle, but noticeable. Where wiring and impedance matter most is in the safety of your amplifier. Using the wrong impedance can seriously damage your amplifier and knowing why and how can ultimately save a lot of headaches and dollars. By utilizing different wiring schemes, a variety of speaker combinations can match the impedance requirement of your amp. Knowing the principles involved and how to figure the math can also allow you to use the speaker combination of your choice.

Impedance
Concerning impedance, solid-state and tube amplifiers react differently. Solid-state amps have a Minimum Load Impedance. Regardless of how the speakers are wired, the sum total of the combined speaker impedance must be equal to or greater than the amp’s Minimum Load Impedance value for safe operation; never use a load that is too low for a solid-state amp. Conversely, tube amplifiers will not suffer damage from a speaker impedance load that is too low but the sound may be muddy or weak. An impedance load that is too high for a tube amp however, will cause high voltages internally that can damage the power tubes or output transformer. For a deeper discussion on speaker impedance, check out this inSync article; https://www.sweetwater.com/insync/speakers-different-impedances/

Series and Parallel Wiring
Series and parallel are the two most common wiring schemes for speakers. A parallel connection tends to smooth out response and have a damping effect on speakers. A speaker has a large impedance increase at its fundamental resonance and can sound boomy or out-of-control, depending on the specifics of the installation. Parallel wiring of multiple speakers will counter-balance this effect, even speakers of the same size since no two speakers are exactly alike. Connecting speakers in series takes away that control, allowing the fundamental to resonate more and also causing a small amount of Back EMF. While theoretically not as predictable, the sound can be more desirable for guitar and is preferred in many situations. Since a lot of modern amps have multiple speaker impedance outputs, experimenting with with wiring options may prove to subtly enhance or tame certain sonic characteristics.

Wiring
Here’s how to wire two speakers in series:

Connect the positive terminal of the first speaker to the positive terminal of the amplifier
Connect the negative terminal of the first speaker to the positive terminal of the second speaker
Connect the negative terminal of the second speaker to the negative terminal of the amplifier.
The negative and positive amplifier connections in a typical guitar set-up are through a 1/4″ jack and cable. The tip connector is normally positive and the ring connector is negative. To figure the impedance load of speakers wired in series, simply add their values together. For example, two 8-ohm speakers wired in series equals a 16-ohm total load.

Here’s how to wire two speakers in parallel:
Connect the positive amplifier terminal to both of the positive terminals of the speakers
Connect the negative amplifier terminal to both of the negative speaker terminals
If all of the speakers individually have the same impedance, divide a single speaker’s impedance by the number of speakers to find the total impedance. For example, two 8-ohm speakers wired in parallel is a total of 4 ohms, or eight divided by two.

Series/parallel is another wiring option, most notably used in vintage 4×12 Marshall cabinets. This allows for the total ohm load of all four connected speakers to be the same as one of the individual speakers. For example: four 16-ohm speakers connected in series/parallel equals a total load of 16 ohms. This wiring scenario has the best qualities of series and parallel, but it does take four speakers to achieve it.

Series/Parallel wiring diagram:
Speaker #1 positive terminal connected to amplifier positive terminal
Speaker #1 negative terminal connected to speaker #2 positive terminal

Speaker #2 negative terminal connected to amplifier negative terminal

Repeat the process, substituting speaker #3 for #1 and #4 for #2:
Speaker #3 positive terminal connected to amplifier positive terminal
Speaker #3 negative terminal connected to speaker #4 positive terminal
Speaker #4 negative terminal connected to amplifier negative terminal
Understanding the basic principles of impedance and how to wire speakers can allow you to confidently and safely experiment with a variety of combinations. While this process requires you to apply specific equations, ultimately your ears will be your best guide to the goal of good tone.

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