Bass Guitar Lessons Online

Ohms and Watts Explained - Part 2

(This article is taken - with modifications - from talkbass.com. Thanks to Dan Garcia for pointing out inaccuracies in the original post.)

 

Hooking Up Multiple Bass Guitar Cabinets

Where all this gets more complicated is when you hook up multiple speaker cabinets to the same head. Let’s look at that…

Series and Parallel

When you hook up more than one speaker to an amp, there are two ways they can be arranged: in series, or in parallel.

 

Series means chaining the speakers (not necessarily the cabinets!) together one to the next. Series circuits are basic types of electrical circuits in which all components are joined in a sequence so that the same current flows through all of them. Nowadays, series configurations are much less common than parallel configurations in bass amp setups.

If each speaker has an impedance below 8 ohms, you should wire them in series.

Careful - If you have two 4 ohm speaker cabinets or one 8 ohm and one 4 ohm speaker cabinet DO NOT connect them to each other (i.e. daisy chain them) from the 4 ohm output of your amp. You can, however, connect/daisy chain two 8 ohm speaker cabinets to a 4 ohm amp output socket. (See below.*)

 

Parallel means sending one output of the bass amp head to one cabinet and a second output from the head to another cabinet. Parallel is two (or more) side-by-side connections. Parallel circuits are types of circuits in which the identical voltage occurs in all components, with the current dividing among the components based on their resistances, or the impedances.

If each speaker has an impedance of 8 ohms or more, then you can generally connect them in parallel.

* If you have an amp that takes a total load of 4 ohms and only one speaker output you can connect/daisy chain two 8 ohm speaker cabinets.

If you have an amp that takes a total load of 4 ohms and has two speaker outputs, then you can connect each speaker cabinet to each speaker output of your amp.

Most of the time you will wire bass cabinets in parallel. That’s how we will wire the upcoming examples.

Calculating Total Impedence of Equal Impedance Cabinets

When you add a second cabinet, realize there are now two places for the amp’s power to go. Adding a second cabinet causes the total impedance (amount of resistance) of the load to change.

It’s easiest having each cabinet with the same impedance (e.g. each cab is 4-ohms, or each is 8-ohms). To determine the total impedance of the cabinets (all with the same impedance), take the impedance of one cabinet and divide it by the total number of cabinets.

impedance of single cab / number of cabs = total impedance

For instance, two 8-ohm cabinets wired in parallel will have a total impedance of 4 ohms. Two 4-ohm cabinets would have an impedance of 2 ohms. Remember, we said if your amp can’t handle a 2-ohm load it could go up in flames. That’s why this is so important. If your amp says it can put out a certain number of watts at 4 ohms, you can only hookup a total load of 4 ohms, 8 ohms, or greater – not 2-ohms!

Calculating Total Impedence of Different Impedance Cabinets

If you are hooking up two cabinets of different impedances, there’s a little more math.

(impedance of cab 1 X impedance of cab 2) / (impedance of cab 1 + impedance of cab 2)

For instance, if you have a 4-ohm cab and an 8-ohm cab:
multiply 4 x 8 = 32
then 4 + 8 = 12
32 / 12 = 2.667 ohms

If your amp is rated only for 4-ohms, you can’t use this configuration of cabinets with 2.667 ohms.

An alternate method is to theoretically treat the single 4-ohm cab as two 8-ohm cabs. When they’re all the same impedance use the prior calculation method: divide the ohms of one cab by the number of cabs. Our same example would be 8 ohms/3 cabs = 2.667 total ohms.

 

 

 

---

Do you want comprehensive bass lessons ... without overwhelm? Then subscribe below.

 

To get 2 lessons a WEEK (12 monthly installments of $38.86 USD)
click the PayPal Subscribe button
(There is no lock-in contract.)

You do not need a PayPal account to use the free and secure services of PayPal when you use your credit card or debit card

IMPORTANT: After your PayPal payment is complete, PayPal will automatically re-direct you to the confirmation/opt-in page so you can begin receiving your lessons right away. If the re-direct does not occur, please press the "Return to Merchant" button to receive the re-direct to your opt-in page.