Home    Parts Store Manufacturers Resources   IFAQs     About  

    Speaker Loads and Wiring



Amplifiers are designed to power a specific "load", meaning a speaker or set of speakers having a specific "AC impedance" measured in ohms.

Impedance resists the flow of electric current so the higher the speaker impedance the less current the amplifier has to supply.  Conversely, the lower the impedance the more current must be supplied.

In other words, a low impedance speaker is a big workload for your amp and a high impedance speaker is a small load.




Most speakers have an impedance of either 4, 8 or 16 ohms (Ω).  To push more air, several speakers (always of equal impedance) can be wired together in a cabinet.

The cabinet impedance depends on how the speakers are wired and may differ from the impedance of the speakers.  Wiring diagrams and their effect on cabinet impedance are displayed below.

An amp works best when driving a load with the same impedance as the amplifier's "output impedance".  If they don't match, there could be consequences:

  • If the speaker impedance is higher than the amp's, the amp might sound weak or dull.

  • If the speaker impedance is lower than the amp's, the amp might sound fantastic but eventually burn out.

For these reasons, amplifier speaker jacks are often marked with the minimum load you should connect (4Ω for example).  Speakers and cabinets should also be marked with an ohms value.  If not, you can easily measure the value with a multimeter:

NOTE:  Multimeters measure DC resistance, not AC impedance.  However, the two values correlate.  The DC resistance is somewhat lower than the AC impedance so round up the meter reading to the closest of 4, 8, or 16 ohms.

Some amps have an impedance selector switch on the rear panel that you can use to match its output impedance to different speaker impedances.  Changing the speaker impedance is one of the easiest and most dramatic ways to change the sound of a guitar amp.

WARNING:  If your amplifier uses output tubes, be sure to have speakers connected whenever the amp is turned on.  Otherwise, the amp's output transformer can easily be damaged, especially if you're playing through it.




There are two ways you can connect two speakers.  One way is called  "series wiring" and the other is called "parallel wiring".

Wiring two speakers in series doubles the impedance of one speaker.  Wiring two speakers in parallel halves the impedance of one speaker.

For example, the diagram below shows you how you can turn a pair of 8Ω speakers into either a 16Ω or a 4Ω load.

Series & Parallel Wiring - 2 Speakers

To make a two-speaker 8Ω cabinet, put two 4Ω speakers in series
or two 16Ω speakers in parallel.




Wiring four speakers in series quadruples the impedance of one speaker.  Wiring four speakers in parallel quarters the impedance of one speaker.

Below, the diagram on the left shows a 16Ω cabinet with four 4Ω speakers and, on the right, a 4Ω cabinet with four 16Ω speakers.

Series & Parallel Wiring - 4 Speakers




A third way to connect four speakers is called "series-parallel" wiring.  It puts a pair of series-wired speakers in parallel with another pair of series-wired speakers.  The combined impedance matches that of one speaker.

For example, the diagram below shows a 4Ω cabinet containing four 4Ω speakers.  Use the same wiring with 16Ω speakers to get a classic, 16Ω Marshall cab.

Series-Parallel Wiring - 4 Speakers

To make a four-speaker 8Ω cabinet,
put four 8Ω speakers in series-parallel.




The diagram below shows the wiring of a Marshall 2x12" speaker cab having a Mono/Stereo selection switch and two specialized input jacks.

When the Mono/Stereo switch is set to "Mono", the two 8Ω speakers are wired either in series (making a 16Ω cab) or in parallel (making a 4Ω cab), depending on which jack you use.

When the switch is set to "Stereo", each jack connects to a separate 8Ω speaker and you use both jacks, one for the amp's left output and one for its right output.

Mono/Stereo Speaker Cabinet Wiring

To make a four-speaker Mono/Stereo cabinet, replace each 8Ω speaker with either two 4Ω speakers wired in series or two 16Ω speakers wired in parallel.  The jack impedances will be the same as above.

Additional Resources:

A Simple, Anywhere Speaker-Tester

Marshall Cabinet Handbook

Jensen   |   Celestion

®See trademark owners  HERE.

          IFAQs      TOP OF PAGE
Home       |       Store       |       Manufacturers       |       Resources       |       IFAQs       |       About

Page design and content Copyright © Richard Diemer - All rights reserved