NEWS

So How Do I Figure Out My Speaker Impedance?

By: Dino Monoxelos

So here’s a quick little article I wrote up to help with those of you who have a hard time figuring out your impedances when using multiple cabinets.

A single cabinet will always list its impedance and power rating somewhere on its input jack (or at least it should, like all Ampeg cabinets do). And in most cases, if not all, in the case of an Ampeg cabinet, it will either be 4 ohms or 8 ohms. Very rarely will you ever see a bass cabinet built in anything less than 4 ohms or greater than 8 ohms. Some guitar amp manufacturers do sometimes build 16 ohm cabinets, but that’s only if they’re designing cabs for their own specific amps.

Back to bass amps… If your amp is 4 ohm stable, meaning it will handle any impedance DOWN to 4 ohms, then either a single 4 ohm cabinet or two 8 ohm cabinets wired in parallel are safe. (NOTE: ALL Ampeg cabinet speaker ins/outs are wired in parallel, as well as all speaker outs on every Ampeg head.)

So What If I’m Running More Than One Cabinet?

There is a mathematical formula that is used to determine total impedance.

Cabinet #1 IMPEDANCE (times) Cabinet #2 IMPEDANCE (over) Cabinet #1 IMPEDANCE (plus) Cabinet #2 IMPEDANCE

(Ω x Ω)/(Ω + Ω)=

So basically you take the sum of cab#1 x cab#2 and divide that by the sum of cab#1 + cab#2.

Example 1: Two 8 ohm cabinets. 8×8=64, 8+8=16. 64 divided by 16 equals 4. Two 8 ohm cabinets wired together in parallel give you a total 4 ohm load.

Example 2: Two different impedances combined. A 4 ohm cab and an 8 ohm cabinet. 8×4=32. 8+4=12. 32 divided by 12 equals 2.67 ohms.

Here’s an easier way to figure it out provided that both cabs are of equal impedance:

Take the impedance of one cab and divide it by the number of cabinets. Two 8 ohm cabs divided by two equals 4. 8 / 2 = 4.

Here’s an even easier way to remember… DON’T LOSE THIS BLOG!

Two 8 ohm cabinets = 4 ohms

Two 4 ohm cabinets = 2 ohms

Two 2 ohm cabinets = 0 ohm (Not a good idea, plus you’ll probably never see a 2 ohm cabinet!!!)

One 8 ohm cabinet combined with a 4 ohm cabinet = 2.67 ohms

One 4 ohm cabinet combined with a 2 ohm cabinet = 1.33 ohms

Hope this helps!

Dino has spent over 25 years in the Ampeg world conducting seminars and clinics all over the globe. He’s also the author of four instructional bass books by Mel Bay and his own publishing company, MonoTunes Music.  His favorite bass to play is his MTD 534-24.