Impedance is something that can make or break your amp- literally! Even a general understanding of it can be a real lifesaver. This article will cover the basics of impedance and how it applies to your bass heads and speaker cabinets, specifically with matching them together.
Ohms and Impedance
The term impedance is used to describe a circuit’s resistance to electrical flow. An easy way to remember this is by thinking of the word impede. When the electricity from your amplifier flows to your cabinet, some of it is impeded. The amount of electricity that is impeded is the impedance. The impedance is measured in ohms, commonly represented with the Greek symbol Ω.
The higher the impedance is, the more resistance there is. This means that a cabinet with an impedance of 8 ohms will pull less power from your amplifier than a cabinet with an impedance of 4 ohms.
Oftentimes, you will hear musicians or engineers use the term load when discussing impedance. In this instance, this term simply refers to the bass cabinet or bass cabinets hooked up to the amplifier.
Impedance: Practical Application
If this all seems complicated, fret not! You don’t necessarily need to understand the technical ins and outs to save your amp from a fiery death. We will walk through a practical example below using a Carvin Audio B2000 bass amplifier and BRx10.4 cabinet.
This is the back panel of a Carvin Audio B2000. On the bottom right hand side, it lists the output power at each impedance. The B2000 puts out 2050W of power at 2 ohms, 1300W at 4 ohms, and 700W at 8 ohms. The amp has a 2 ohm minimum load, meaning that it will not be able to handle a load that is below 2 ohms.
B2000 Bass Amp Back Panel- Note Output Power Ratings On Lower Right
BRx10.4 Bass Cabinet Back Panel- Note Impedance Rating of 4 Ohms
If you decide to use an 8 ohm cabinet, the B2000 will put out 700W of power into that cabinet. To get the full 2050W of power from the head, you need to provide a 2 ohm load and will likely have to hook up multiple bass speaker cabinets (since 2 ohm cabinets are very uncommon). This is where we have to go back to math class for a little bit!
Let’s say you’re playing a big gig and want to bring along two Carvin Audio BRx10.4 bass speaker cabinets and wire them in parallel to the head- that is, hooking up each cabinet to the B2000 with its own speaker cable. To calculate the total impedance of this load, we will use a simple formula (assuming the impedance of each cab is the same):
Impedance of single cab / Total number of cabs = Total impedance
Plugging in the numbers from the BRx10.4 (just like in math class!) the formula looks like this:
4 ohms/ 2 cabinets total = Total impedance of 2 ohms.
So, using two BRx10.4 cabinets will give you an impedance of 2 ohms and pull 2050W of power from the B2000. You cannot hook up any more cabinets at this point, as you have already reached the specified minimum impedance of 2 ohms!
If you are using two 8 ohm cabinets, the total impedance for your load will be 8/2 = 4 ohms. If you want to use four 8 ohm cabinets, the total impedance will be 8/4 = 2 ohms.
Carvin Audio also offers an impedance calculator application that calculates the total impedance of all cabinets in your load. So if you want to double check your math or just don’t want to do math, this handy app is a lifesaver!