Connecting Speakers to a Guitar Amplifier

For many people, attaching speakers to guitar amps is a mysterious process.  They are aware that there are “rules” you have to follow, and that the rules involve something called impedance, and terms like “series” and “parallel,” but what do those things mean, and how do you connect them so that your amp doesn’t burn up?

First, what do we mean by the terms “series” and “parallel?”  Experts make many analogies regarding this subject, but in the end, the example of hydraulics seems to hit home with most people – think of your standard garden hose.

Imagine the big water tank in your neighborhood.  Now imagine a valve welded on to the side of that tank, and your little ½” garden hose attached.  There is a great deal of pressure, but you only get so much water from your hose. That little hose puts up some resistance.  Does it help the situation to add another hose to the end of the one you have?  Well, actually, it makes things worse, doesn’t it?  Since the hose is now twice as long there is much more resistance, and it takes a great deal more pressure to get the same amount of water.

If we wanted even more water, we could go back to the tank and weld on many more valves to which we attach more garden hoses.  Now when we turn them all on at the same time, we get many times more water at the same pressure.   If we need more water, we add more hoses to the tank.

The first example is of a series circuit.  Adding a hose to the end of the first one has the effect of adding resistance.  The second example is of a parallel circuit – adding a hose at the tank has the effect of reducing the resistance.

You may be able to see that when you added an identical hose in series, you doubled the resistance, but when you added it in parallel, you divided the resistance in half.  This is exactly how electronic impedance is calculated.

Before we talk about our speakers and cabs, you may see the terms Impedance and Resistance used in the same context.  One reason for this is that many of the calculations for resistance and impedance are the same.  Impedance is the correct term for this discussion since it is an AC measurement, and sound waves are AC (Alternating Current).  There is a place for the use of the term Resistance as pertains to speakers, but we are going to ignore this for the purposes of this discussion.

OK, onward!  First, let us talk about connecting speakers in a cabinet.  The cabinet can be a stand-alone box, or the speakers in your combo – it does not matter which.  They work the same, either way.

How shall we connect the wires for a series cab?  This diagram illustrates how we would connect two 12” speakers together in series.  Wiring 10” speakers, 15” speakers, or 2” speakers would be the same.  This example works for all of them.  Here is how it would look:

2x12 Series Connection
Two Speakers in Series

We wire the tip of the plug or jack to the plus of the first speaker, then wire the minus of that speaker to the plus of the second speaker, and wire its minus to the sleeve of the plug or jack.  However, what impedance have we got?  The following table shows all of the possible impedances for the standard 4, 8, and 16 ohm speakers.  Do not use the grayed out rows:

2×12 Series

Speaker 1

Speaker 2

Total Impedance

Jack to Use

4

4

8

8

4

8

12

8 *

4

16

20

8

8

16

16

8

16

24

16

16

32

* – One speaker will be louder

What happens when we switch the same two speakers to parallel wiring? Here is what that looks like:

Two Speakers in Parallel
Two Speakers in Parallel

As you can see, we wire the tip to the plus terminal on both speakers, and the sleeve to the minus terminal on both speakers.  The following table shows all possible impedances using 4, 8, and 16 ohm speakers. Do not use the grayed out rows:

2×12 Parallel

Speaker 1

Speaker 2

Total Impedance

Jack to Use

4

4

2

4

8

2.6

4

16

3.2

4 *

8

8

4

4

8

16

5.3

4

16

16

8

8

* – One speaker will be louder

What happens if we wish to wire up three speakers?  Although this is unconventional, there are several notable examples of combos coming with three speakers.  If we put them in series, this is what it looks like:

Three Speakers in Series
Three Speakers in Series

It is wired the same as the 2×12 example above, except there is one more speaker in series.  Here are the possible impedances from 4, 8, and 16 ohm speakers. Do not use the grayed out rows, as the speaker impedance is too high:

3×12 Series

Speaker 1

Speaker 2

Speaker 3

Total Impedance

Jack to Use

4

4

4

12

8

4

4

8

16

16 *

4

4

16

24

4

8

8

20

4

16

16

36

8

8

8

24

16

16

16

48

* – One or more speakers will be louder

What happens if we wire three speakers in parallel?  This is what that would look like:

Three Speakers in Parallel
Three Speakers in Parallel

Again, it is just like the 2×12 example, but we have connected one more speaker.  Here are the possible impedances using 4, 8, and 16 ohm speakers. Do not use the grayed out rows, as the impedance is too low:

3×12 Parallel

Speaker 1

Speaker 2

Speaker 3

Total Impedance

Jack to Use

4

4

4

1.3

4

4

8

1.6

4

4

16

1.7

4

8

8

2

4

8

16

2.3

8

8

8

2.6

8

8

16

3.2

8

16

16

4

4 *

16

16

16

5.3

4

* – One or more speakers will be louder

When we get to 4×12, we get to explore three ways of wiring: Series, Parallel, and Series/Parallel.  If you think back to the garden hose analogy, if we wanted an exact amount of water to flow, and could connect garden hoses in series, or parallel to achieve it, you might connect some in series and others in parallel to get to the value you need.  This is what we do with speakers as well.

First, let us look at 4 12 inch speakers in series to see how that wiring looks:

Four Speakers in Series
Four Speakers in Series

It looks very similar to the 2×12 wiring except we put twice as many speakers in series.  Here is the impedance chart for 4×12 series.  Once again, do not use the grayed out rows.  Notice there is only one configuration that will work in this instance!  As the speakers add impedance, the value goes up very quickly in series, producing nearly all combinations that are too high for your amp.

4×12 Series

Speaker 1

Speaker 2

Speaker 3

Speaker 4

Total Impedance

Jack to Use

4

4

4

4

16

16

4

4

4

8

20

4

4

4

16

28

4

4

8

8

24

4

4

8

16

32

4

4

16

16

40

4

8

8

8

28

4

8

8

16

36

4

8

16

16

44

4

16

16

16

52

8

8

8

8

32

8

8

8

16

40

8

8

16

16

48

8

16

16

16

56

16

16

16

16

64

What about 4 12 inch speakers in parallel?  Here is what that looks like:

Four Speakers in Parallel
Four Speakers in Parallel

Here is the impedance table for 4 12 inch speakers in parallel.  Notice once again, there is only one row of the table that identifies a combination that will work for your amp.  All of the others are too low for your amplifier to work correctly.

4×12 Parallel

Speaker 1

Speaker 2

Speaker 3

Speaker 4

Total Impedance

Jack to Use

4

4

4

4

1

4

4

4

8

1.14

4

4

4

16

1.23

4

4

8

8

1.33

4

4

8

16

1.45

4

4

16

16

1.6

4

8

8

8

1.6

4

8

8

16

1.77

4

8

16

16

2

4

16

16

16

2.28

8

8

8

8

2

8

8

8

16

2.28

8

8

16

16

2.66

8

16

16

16

3.2

16

16

16

16

4

4

What happens if we wire as a Series/Parallel configuration?  Here is how that looks:

Four Speakers in Series/Parallel
Four Speakers in Series/Parallel

Speakers one and two are in parallel and speakers three and four are in parallel.  However, those two sets are wired in series, by virtue of the way the plug (or jack) is wired, and the wire between the two sets of parallel-wired speakers. This is the hardest configuration to understand, but look what happens to the table below – every combination produces usable impedance values!

4×12 Series/Parallel

Series

Parallel

Parallel

Speaker 1

Speaker 2

Speaker 3

Speaker 4

Total Impedance

Jack to Use

4

4

4

4

4

4

4

4

4

8

4.6 *

4

4

4

4

16

5.2 *

4

4

4

8

8

6 *

4

4

4

8

16

7.3 *

4

4

4

16

16

10 *

8

4

8

8

8

6.7 *

4

4

8

8

16

8 *

8

4

8

16

16

10.7 *

8

4

16

16

16

11.2 *

8

8

8

8

8

8

8

8

8

8

16

9.3 *

8

8

8

16

16

12 *

8

8

16

16

16

13.3 *

8

16

16

16

16

16

16

* – One or more speakers will be louder

Notice that any time you combine speakers of different impedances, there is an asterisk with a note that one or more speakers will be louder.  This is why you always find speakers of the same impedance in a cabinet.  You could avoid this by using speakers that are more sensitive for the higher impedance speakers. There is no guarantee that the speakers that have the sound you want will be the sensitivity you need to achieve equal volume.  You are better off simply using the same impedance for multiple speakers, but people do all kinds of crazy things that work for them. Let your ears be your guide.

What happens when we combine speaker cabinets?  You may treat a speaker cabinet exactly as an individual speaker.  That is to say, once you know the impedance of a cabinet, you can combine it with other cabinets exactly as we have shown above for speakers.  You typically deal with cabinets at the jack instead of at the speaker terminals, so there are a couple of tips, as follows:

For Dr. Z cabs, there is usually only one jack, so to use two cabinets, you need a Y cord adapter.  You can purchase these at a number of places.  Be sure to get a Y cord for speaker use, as a low-level signal Y cord would not be sufficient for the current expected while driving speakers.  You could damage your amp if the Y cord failed while you are playing.  Get the heavy-duty speaker Y cord.

Imagine we combine two cabinets with a Y cord.  What impedances do we have to deal with?  Here is what that would look like:

Two Cabinets Combined by "Y" Cord
Two Cabinets Combined by "Y" Cord

On the left, you see two cabs connected to a “Y” cord that we connect to the amp. The image on the right shows what a Y cord may look like: a plug wired to two jacks. Make sure you get a Parallel Y cord. So what impedances will we get when we connect like this? Here is the impedance chart. Notice that it is identical to the parallel-wired speaker chart above!

2 Cabs in Parallel (Y Cord Method)

Cab 1

Cab 2

Total Impedance

Jack to Use

4

4

2

4

8

2.6

4

16

3.2

4 *

8

8

4

4

8

16

5.3

4

16

16

8

8

* – One or more speakers will be louder

What about the case where the speaker cab has double jacks wired in parallel?  Here is what that looks like:

Two Cabinets in Parallel
Two Cabinets in Parallel

Here is the impedance chart for this configuration.  Notice again that it is identical to the previous chart and to the chart for parallel-wired speakers.

2 Cabs in Parallel (Parallel Jack Method)

Cab 1

Cab 2

Total Impedance

Jack to Use

4

4

2

4

8

2.6

4

16

3.2

4 *

8

8

4

4

8

16

5.3

4

16

16

8

8

* – One or more speakers will be louder

Good luck!