I'll try to keep this simple, but it's actually a crucially important topic in AC electrical / electronic engineering and it's helpful to have a working understanding of it when you're shopping for gear. If anyone finds any BS in this post, oh god please say so.
Peak is the upper excursion of an AC waveform, either positive or negative. Think of it as "absolute distance from zero." Peak-to-peak is the distance between the positive and negative waveform peaks both.
If you're sitting at 0, and you have a waveform lift your voltage by 10 volts to +10, you have a 10 volt peak.
If you're sitting at 0, and you have a waveform drop your voltage by 10 volts to -10, you have a 10 volt peak.
If you have both happen, you have a peak-to-peak of 20 volts.
So far so good.
Watts = volts * amperes. That means that if, say, you have 1 ampere flowing at each peak, you have 10 watts positive and 10 watts negative, for a total of 20 watts peak-to-peak.
This means that you would have a speaker with an impedance of 10 ohms and the peak current is 1 amp peak. All of these relate to each other using Ohm's laws, but you need to keep units straight.
If your amp is putting out 100W peak at, say, 50 volts, you're putting out 2 amperes of current at the peaks and 70.7W RMS.
Here's where things start going wrong. If you have 50 volts peak, you would have (50/1.414)Vrms = 35.3Vrms and your power based on RMS value will be 50 watts. You missed the squared factor in the power equation... if you use 2 amps peak, you need to also convert the current to RMS, use (2/1.414)Arms = 1.414A... now 35.5Vrms x 1.414Arms = 50 watts based on RMS measurements.
If your speaker is seeing 4 amps of current, and you're pushing it to 100W, your amp is swinging 25 volts at the output.
Without defining peak, or RMS measurements, power is no longer defined.
Watts, voltage, and amps are all often expressed in terms of peak, peak-to-peak, and RMS.
Peak has no practical value to a periodic bipolar waveform, and all (common) audio measurements are made using either peak to peak, or RMS measurements when describing periodic bipolar waveforms. This also makes the math more consistent.
RMS is similar to the "average power" rating some manufacturers quote, but is actually somewhat lower. Average power is the average wattage output over a given amount of time. As far as I know, there is no standard for this and this rating is garbage. Never even bother to read it. Marketing people like it better than RMS because it's always bigger.
This is not accurate. For a non-distorted sinusoidal waveform, the average and the RMS rating will be identical. Where average and RMS diverge is when the waveform is distorted, contains additional harmonic elements or has a different peak voltage than a pure sinusoid would have. There are also differences in how meters read distorted waveforms depending on the algorithems used to detect and calculate the measurement. What "RMS power" (power based on RMS voltage and current measurements) really means is the effective heating capacity of the waveform.
Peak is RMS * 1.414
RMS is peak * .707
RMS is also (peak-to-peak / 2) * .707
Still with me?
1.414 is the square root of 2 out to 3 decimals. That's what the "Root Mean Square" stands for.
Whoa here, it's a whole lot different than this. Here's a pretty good link showing what it really means and how/why it's used:
https://en.wikipedia.org/wiki/Root_mean_square
If a cab is rated for, say, 100W RMS, it should take 1.414 * 100W, or, 141.4W peak, all day.
If a cab is rated for 500W peak, it's also rated for 500 * .707 watts, or 353.5W RMS.
Nope, that pesky squared factor got dropped from your voltage/current equation. BOTH need to be expressed as RMS values and then when you multiply the RMSxRMS (which become the squared factor in the V**/R or I**2R power equationa, factors you get 1.414 x 1.414 or 2. So peak power = 2x "RMS power".
Peak-to-peak is twice peak, so divide peak-to-peak by two and the multiply by .707 to find the RMS rating if they give this figure.
Nope, again you have crossed units up and need to specify if you mean voltage or power.
So what does it mean?
The RMS rating is what your cab is designed to handle all day without getting too warm. It's your "ideal dissipation," and is often called "continuous power." Many manufacturers fudge these figures, so take published specs with a grain of salt. No spec sheet can tell you if your amp will sound good with any cab.
Generally, this is the power that a speaker can handle over an extended period of time (the time period is an essential part of this by the way) but this too is a function of frequency as there are specific cooling effects that are present at lower frequencies but do not exist at frequencies above say 300-500Hz. Fortunately, most bass guitar signals exhibit falling power with frequency... this is not true with many guitar signals however.
A speaker can take a lot more power in transient peaks that don't last but a few milliseconds than they can take constantly. Hence the peak and RMS ratings.
I'm a bass player, not a hi-fi nerd, so I don't give a $%& about slew rates and other esoteric BS that a musician isn't worried about. I just want to know if my amp will blow up this cab or not, and if the cab can reproduce the frequencies I want to hear. For that I look at the RMS rating and the frequency response graph, and that's it.
First of all, the industry accepeted meanings of peak, program and RMS have not been discussed and all of this is being taken out of context. I will discuss what these 3 ratings GENERALLY mean in another post.
IMO, it also helps to understand what all of this means and in fact there's a lot more that goes into developing a meaningful speaker rating, one that holds up to REASONABLE expectations under REASONABLE use in the real world.
