Root Mean Squared is average or constant power where peak is just that; a peak or transient. Think about it like this. Something like a snare hit would be a peak because it's energy is a sharp burst and only there for a short duration (peak). versus something like a continuous tone that doesn't very in amplitude (average). Now this is an over simplification and one could argue that even a sine wave of non verying amplitude has a peak power reading (the tips of each individual cycle) and an RMS reading (its average power).
Wattage and speakers and Ohms...oh my!
There's no place like Ohm... There's no place like Ohm... There's no place like Ohm...
OK Dorothy, you get the picture. Do any of these questions sound familiar?:
1. How can I get my speaker's Ohms lower so my amp will put out more power?
2. What do series and parallel mean?
3. What are impedance and resistance?
4. How do I calculate impedance?
5. Do I need 400 Watts to drive a 400 W speaker?
6. Can you really under-power a speaker?
7. What is clipping?
8. How much power do I need?
9. What is headroom?
10. Why isn't this 400 Watt amp twice as loud as my old 200 Watt amp?
11. How do I make it LOUDER?!?!
These questions and many more like them get asked every day. And depending on whom you ask, you can get a wide range of (sometimes very wrong or misleading) answers. Once again this is a subject that could cover volumes. This will be the abridged "layman's" version. So if you already know all of this and it sounds like I'm being overly simplistic, please bear with the rest of us.
Most of you know that your power amp is rated to put out a certain amount of power into a certain Ohm load...right? You know, in the specs where it states 800W @ 4 Ohms, 500W @ 8 Ohms, etc. First off, why does it put out more power into lower Ohms? Ohms are a measurement of resistance or impedance (yup, they mean the same thing). So think of it like plumbing. Which pipe will flow more water: a 1/2" pipe or a 1" pipe? The 1" pipe right? Sure. And the reason is that it poses less of a hindrance (resistance) to the water. With that in mind, which speaker will let your amp "flow" more power: an 8 Ohm or 4 Ohm? You got it! The 4 Ohm has less resistance, so the amp will push more power into that load. Does this mean that a 4 Ohm speaker is louder than an 8 Ohm speaker? All other things being equal, not really.
This takes us to a common misconception: "more Wattage = more volume". Many people think that if they need more volume, they need to pump up the power. While more power will surely increase volume, the power must grow exponentially to make a major difference in volume. In other words, it takes 10 times the power to double your volume (and that's assuming your speakers can handle 10 times the power). The best way to increase your volume is to increase the number of speakers. Say you have an amp that puts out 500W per channel @ 8 Ohms and 800W per channel @ 4 Ohms driving two 8 Ohm 15" woofers in their own cabinets. Right now the woofers are getting up to 500W each. If you traded your amp for one that puts put 1000W per channel @ 8 Ohms your volume capability would only slightly increase (because you still only have two 15" speakers). On the other hand, if you added two more identical speaker cabinets with the same amp, you would double your coverage (actually, your acoustic output could quadruple). In this set-up, each speaker box would only be getting 400W vs. the 500W or 1000W but you would have up to 4 times the acoustic output.
Why? Your ears work by picking up the way air is moved. More speakers move more air, period. I told you it might sound simple...
Why do two 8 Ohm speakers = 4 Ohms? It's the LAW I say, it's the LAW! Ohm's law that is. Yeah, Ohm was a real person and he figured out the physics of electrical resistance and made up some cool equations to help us calculate impedance. First, you need to know whether the speakers are wired in "series" or "parallel". Series is wired positive to negative to positive to negative (fig. 1). For series wiring the equation is simple addition. Just add up the total impedance (in Ohms) of all speakers in the loop. Two 8 Ohm speakers in series = 16 Ohms. Very Easy. For parallel, it isn't as easy. Parallel wiring is positive to positive, negative to negative (fig. 2) and the equation is: "The quotient of the inverse of the sum of the inverse." Huh?! Calm down. Take those same two 8 Ohm speakers and invert their impedances, and then add them together: 1/8 + 1/8 = 2/8. Then invert again and divide: 8/2 = 4. It's a little tougher with non-like numbers, but if you're up on your fractions you should be fine (or you can always get some 8 year old to help you).
Now that you are all experts at calculating impedance, keep in mind to never load an amp down below its rated impedance. If you do, it will "try" to push more power into the lower resistance beyond its capabilities and at best it will thermally shut-off (Carvin amp), and at worst (with the other guy's amp)...poof! - you have an expensive new paper-weight! What's with the ratings on speakers and how much power do I really need? Good questions. Power ratings on speakers are just that: Ratings. Power ratings don't determine how loud it will be, how good it will sound, or even how it will stand up to physical abuse. The power rating tells you one thing: how much heat the speaker's voice coil can dissipate (in Watts) before it burns up.
Then why not just run 10 Watt amps driving 10 Watt speakers? Wouldn't that create the same amount of volume? Actually, that would work fine at low volumes. Your everyday home stereo 100W amp, although rated much higher, typically doesn't run at more than 5 to10 Watts RMS average. It may peak at 80 to 100 Watts, but the average RMS output is far lower than you'd think. But you don't get something for nothing. Let's face it, a race car goes faster than a passenger car because it has a ton more power. Same idea works for speakers. If you want to move a lot of air, as in a pro sound environment, you need a device (speaker) that is big enough and mechanically capable of moving that amount of air. Then, you need a certain amount of power (Wattage) to properly motivate that device. Big device, moving lots of air = lots of power.
And you also want "Headroom" Headroom is basically available power that you don't use most of the time. Then why pay for it? Well, as stated earlier, your home stereo may only average 10 Watts RMS, but on loud passages in the music, it may peak to its full 100 Watt potential. These peaks may only last fractions of a second but without that reserve power, the sound of your music would suffer terribly. . So what that other 90 Watts you paid for does is prevent your amp from clipping (distorting) during peaks. Think of it as "sound insurance". Headroom is the reason you may see a sound engineer running an amp that seems much too powerful for the speakers. An experienced sound engineer knows that most speakers are blown due to a power amp running out of "clean" power and clipping and not from being "over-powered" with clean Wattage. I have heard it so many times: "why did my speakers blow?!? They can handle 600 Watts and I was only running a 200 Watt amp on them!!" What that person failed to realize was that by badly mismatching his amp and speakers, he ended up pushing the power amp so hard that it was constantly clipping. Clipping causes the amp to put out damaging DC (direct current) to the speakers and eventually burns them up. That is where the old myth that "you can under-power" a speaker comes from. You can't really under-power a speaker as long as the power is clean. But using a low powered amp to try and push high powered speakers will inevitably lead to clipping and damaged speakers. This doesn't mean you can just throw tons of clean power at your speakers and feel safe, it just means you have to think ahead when putting together your system. Don't go over-board or under-board. If you're going to run some 600 Watt mains, then use a quality amp that will deliver between 400 and 800 Watts at the speaker's rated impedance. Go on the high side if you think you will be really pushing the speakers hard so your amp will be able to handle the peaks without distorting. If your speakers will never see anything larger than a coffee-house, the lower powered amp will probably be fine. Just watch and listen for clipping.
So let's recap: You now know how to calculate your total impedance, you know that the best way to get more volume is to add more speakers, and you know how to properly match your amp and speakers so that you have sufficient headroom and prevent clipping. No matter what speakers and amp you use, always keep your eyes and ears alerted for signs of something being pushed too hard. There are usually warning signs long before something goes "boom". If it sounds crisp, clean and punchy, and not distorted, muffled and muddy, you're doing it right.
Now pay no attention to that man behind the curtain...
Way I got a basic understanding of rms and peak values a long while ago was when someone told the then-idiot me "60W rms is what real raw power your speakers can handle continuously, 120w peak is a signal spike that a 10W multi-media speaker can handle for a fraction of a second without blowing!"
Guess what....I opened up my so-called 120W (peak) multi-media speakers and really actually found only a 10W speaker inside (coincidence?).
Mind you, you'll get to know that it's a little more complicated than that but if you contemplate a little on it, you will find it easier to understand the difference between rms and peak in the future.
The peak power rating of a speaker may be may time the rms rating as the failure mechanisms are different.
Exceeding the Maximum rms power causes over heating of the speaker. It damages the speaker by distorting, melting, burning parts or other heat relate failures; usually the coil windings.
Exceeding peak power results in excess coil motion. The coil may be pushed out of the magnet or the cone may tear.
If you drive the speaker with a simple sign wave the peak power is twice the rms power for example 10 Watts is 20 peak Watts.* When listening to music, a cymbal crash may cause the peak wattage to be may times the rms wattage.
*watts = volts * amps. When volts and amps are read with a true reading rms meter a sin wave generates a value equal to the square root of 2 of the peak voltage or current. As a result rms wattage values are half as high as peak (.707*.707=.5). For wave forms other than sin waves the ratios are different. For example: 1) A square wave’s peak and rms power are the same. 2) A short rectangular pulse of 10V and 10A with the duration of .01 seconds occurring once a second would produce a peak of 10V*10A=100W peak. The RMS wattage would only be 1W