Ohms and Amps - Posted on 2014-12-18 by Felix Nieto

Hey guys,

So today we are going to be talking about Ohms. Oh joy right! Well while it can sound like a boring topic this is a very useful one that will help you out in the long run. Ohms, in its original sense, is a form of resistance or the ability to impead the natural flow of electricity. So im sure your wondering to yourself, how does this relate to me? Well as a sound engineer or musician this is valuable information. It determines how you connect your amps, monitors, and speakers to get the best results and save yourself some problems like burning something out. 

Lets talk about amps because this is an area i feel like a lot of musicians maybe unaware of this topic so lets clarify. In order for your amp to be most efficient and work at peak performance the Ohms must be matched. This means that if on the back of your guitar/bass amp head it says the impedance output is 8 ohms, then the cabinet your connecting better be 8 ohms. Most people understand this part but here is where they get confused. What happens when you need to connect another cabinet to your amp because your drummer is just way to uncontrolably loud since he got his new cymbals? Well the thing is you cant just stick it in the second output port of your amp and call it a day. If you did, your ohms would be mismatched with your amp and bad things could happen. Instead you have to do a quick calculation to determine your new ohmage or impedance of the two combined cabinets.

Before you start your calculations you have to figure one more thing out. Which way the speakers are wired. They could be wired in parallel meaning that when you add a second cabinet your going to be decreasing the ohms, or they could be in series meaning they are connected together so you add the impedance. Lets say your cabinets are 8 ohms and your head is wired in parallel. That means that you divide the ohms by the number of cabinets you want to hook up (lets say 2). So that will give you an impedance of 4 ohms. So instead of hooking them both into that 8 ohms output rating you have to be sure to switch it to the 4 ohms one now. If your head was wired in series then you would want to hook then into the 16 ohms port. There is an actual formula for figuring it out. Its (ohms X ohms)/(ohms + ohms). This formula is really only useful when you add mismatched ohms like if one cabinet was 16 ohms and another was 4 ohms. Besides that you will probably not need this.

While it may take just a couple seconds longer to figure out instead of just jamming the speaker cord into the socket, it is an important thing to always keep in mind when connecting speakers. Now days some amps will tell you how to hook it up like the amp below, but not every amp will which is why you need to remember this. 

So to finish up this topic, just always be cognizant when wiring speakers up so you dont have any problems or mismatched impedances. Trust me, taking a little extra time to ensure everything is working properly when installing will save you a lot of time and money in the end. 

So friends, go make better mixes and ill see you on the next one!

- Felix Nieto