Watts... RMS vs Peak / Max
In the car audio and consumer electronics world, you hear a lot about watts, power output and power handling. Companies constantly advertise that their speakers can handle 200 watts or that their amplifier puts out 1,000+ watts. Most people generally shop for amplifiers and speakers simply by looking at which one has the highest power rating, because everybody has heard "the higher the watts, the louder the sound."
But if you take a closer look at the products when shopping around, you'll notice that some manufacturers rate their products' power capabilities with "peak" watts, and some use "RMS" watts. Many show both ratings. At first glance, you might be thinking, "Product A is better because is advertised at 100 watts, while Product B only has only 50 watts." Upon closer inspection, you'll notice that Product A is advertising "peak" watts, while Product B is advertising "RMS" watts. If you look closely at the back of the box, you'll likely see that both products are actually rated the same: 100 watts peak / 50 watts RMS. Some products may even show "max" watts. You might be scratching your head wondering what these terms mean. Well, we'll explain in a minute.
First, in order to understand the differences between "RMS watts," "peak watts" and "max watts," we need to first break down what these terms mean. To help you understand this, we've created a very simplified graph that represents sound as viewed as a waveform on an oscilloscope.
RMS Watts is the continuous power output of an amplifier or power handling of a speaker
Looking at the graph above, the red line represents the sound waves at various watts. The peak power rating is literally the "peak" of the waveform on the oscilloscope – the maximum voltage that the waveform will ever reach. Often times this peak value lasts only a fraction of a second. RMS, on the other hand, is an acronym for Root-Mean-Square and is essentially the average effective value of the waveform. But what does all that mean?
We'll break it down for you:
To put it into layman's terms, peak power is the absolute highest amount of voltage the amplifier can put out before failing – and usually this peak wattage can only be sustained a fraction of a second before causing catastrophic failure of the amplifier. The same holds true for speakers – peak power handling is the absolute highest amount of voltage that speaker can handle for a split second without blowing. There is no clear definition of what peak is or how long this level can be sustained, but it's usually very short.
Many manufacturers also use a maximum (max) power rating. A max power rating generally indicates the maximum amount of power that can be safely sustained without resulting in failure. Typically, this is a more realistic maximum specification than the arbitrary use of peak power.
RMS power on the other hand, is how much power that amplifier will continuously put out – or how much continuous power your speaker can handle. RMS values are typically much lower than peak power ratings, but they more accurately represent what an amplifier or speaker is truly capable of. Think of RMS as a true listening rating. Although not a perfect means of comparison, most RMS ratings are comparable – especially when measuring among name brand products.
So what should we take away from this? When shopping around for a speaker or amplifier, it is important to look for the RMS power rating. Remember, peak power is simply the absolute highest amount of power the amplifier or speaker can handle before failing. Max power is the highest amount of power that can be safely sustained. RMS is continuous power handling at sustained listening level. The RMS power rating will be the closest to the amplifier or speaker's actual capabilities.