Power Ratings

Many people are confused by amplifier and speaker power ratings. Talking about 8 ohms, 4 ohms, and 2 ohms can be confusing to beginners and experts alike. However, matching your amplifier to your speaker does not have to be a difficult task if you understand a few simple ideas.

First of all, we need to understand speaker resistance (aka: impedance), measured in Ohms. Ohms are a unit of resistance. Think of loudspeakers as resistors to electrical current. An amplifier provides power (measured in watts) and a speaker provides resistance to that power (measured in ohms) by converting it into acoustical energy.

So when we talk about an amplifier's power rating, we say it provides a certain power (in watts) into a certain resistance (in ohms). The relationship between power and resistance is defined in Ohms Law. The details of Ohms law are beyond the scope of this guide.

What we do need to understand about Ohms Law is that it works contrary to what may seem logical. This means that when you increase the resistance of your system (for instance, adding another speaker), the number of Ohms reduces (and vice versa).

Another important idea that may seem contrary to what is logical is that you want an amplifier that is capable of providing the same or MORE power then what the speaker is rated for. Under powering a speaker is often the cause of more damage then overpowering. Amplifiers that have a higher power rating then a speaker will work more efficiently then one with a lower rating. They will generally provide better sound quality, tighter bass, and clearer high frequencies. The key is for you to listen for distortion and watch the amplifier signal level indicators for clipping. If you hear distortion, or see the amp clipping, then you are running the system too high; turn it down!

8 Ohms: For instance, lets say we have an Alto MACRO 1400 amplifier that is rated at 310 W at 8 ohms and a Community MVP 35 (an 8 ohm speaker) that is rated at 200 W. This amp/speaker combination will work well because the amp is capable of delivering more power then the speaker is rated. The amplifier will work efficiently.

4 Ohms: Lets say that we add another MVP 35, in parallel, to our system (on the same amp channel). This can be accomplished by running a speaker cable out of the back of the first MVP 35 and into the second. Now, the resistance has doubled, and the ohm rating reduces (see 3 paragraphs above). Our system is now running at 4 ohms, and the amplifier is providing 450 W to each speaker. This means that you are getting more "bang for your amplifier buck". You will have more output coming from your speakers.

2 Ohms: Lets say we add yet another MVP 35 to the system. Once again, the resistance has increased, and the ohm rating reduces to 2 ohms. The power output is now 800 watts to each speaker. Now it is getting dangerous. When resistance is that low, and power is that high, the amplifier risks clipping. It is getting very close to its maximum performance level. It is also getting very hot, and heat is electronics' worst enemy. We do not recommend that you run your system at 2 ohms unless you are an experienced engineer and you know what you are doing.