Apparently we’re here again… Asking “How many Watts can this amplifier deliver?" is like asking, “How long is this rubber band?”
How can a Peak Watt be different from an RMS Watt? They can’t because it’s not the definition of the Watt that changes. The difference is in the duration, in how long the amplifier can continue to produce/pass a given “power” level. BUT, as usual, that’s NOT the whole story. The reason is that Watts don’t exist. What I mean by that is that Watts are extant only through the passage of time and that they are calculated from other inputs. And when it comes to loudspeakers, those other inputs are constantly in flux...
How do you make 100 Watts? You don’t. You can consume 100 Watts, which is to say use 100 Watts, but, unless you’re a generating station, you can’t directly “make” 100 Watts. But let’s say you have need of 100 Watts. How do you get there?
There are an infinite number of ways. For simplicity, let’s pick two familiar starting points. First, let’s assume you want to power a “100 Watt” lightbulb. (Ancient history, I know, but these existed before LEDs.) Let’s first consider a 100 Watt lightbulb made for use in a land that provides household supply of 120 Volts AC. The requirement would be for the lamp filament to reach 144 ohms at operating temperature, which is obviously white-hot! Some of the Watts are producing useful, desirable light, some are producing waste heat, but what percentage of the “real Watts” are waste heat and what percentage are useful light are not relevant in the calculation of the Watts the lightbulb is using. It’s using 100 Watts.
Some parts of the world operate on household supplies of 240V, and in order to make a 100 Watt lightbulb that operates on 240V, the filament would need to reach 576 ohms at operating temperature. A decidedly different filament needs to be used to achieve the result of a 100 Watt lightbulb. And it’s likely that the relative percentage of the “real Watts” providing useful light compared to waste heat will be slightly different. But this lightbulb is also using 100 Watts.
Would you ever consider checking whether the 100 Watt lightbulb you purchased is actually using 100 Watts? Maybe it’s using 110Watts! Wouldn’t that be awesome? Or would it be better if it wasn’t using all 100 Watts? If it was providing the same light as a 100 Watt lightbulb but used only 80 Watts, would that be better or worse? If it did use only 80 Watts and produced the same amount of light, should it be called an 80-Watt lightbulb or a 100 Watt lightbulb or a 100-Watt equivalent lightbulb? How could it be a 100-Watt equivalent lightbulb if it used only 80 Watts? There would have to be something else that could be measured and compared. What would be more relevant to a lightbulb than the number of Watts it uses? How much light it produces? Thats light output, not Watts consumed. After nearly a century of buying lightbulbs by “Watts”, did the realization finally come that the light output is more important and more relevant than the Watts consumed? How did that happen? Someone, somewhere had the realization that referencing how much power something uses, rather than what it provides for that power, doesn’t in any way capture the efficiency or the beneficial value of the product in question.
By the way, on average those incandescent lightbulbs use about 15-30 of the 100 Watts producing light and about 70-85 Watts producing heat. So there are some 100 Watt lightbulbs that are more efficient than others. Which one would you buy?
OK, so that’s a 100 Watt lightbulb, and those are “real Watts” because they are being consumed constantly. (Well, for as long as the switch is left on, or about 1000 hours on average for a 100 Watt filament lightbulb.) Lightbulbs don’t use “peak Watts”. Or do they? The filament needs to be white-hot for it to reach 144 ohms, but when it’s cold it doesn’t resist the flow of electricity nearly as much. The filament is a resistive wire in a vacuum or inert gas-filled chamber. Its resistance to electrical flow makes it hot. Very hot. The flow of current when power is applied is far greater as the filament heats up than once it reaches operating temperature. The peak current can reach as high as 14X the normal operating current. The good news is that lamp filaments have very little thermal inertia, so they come up to temperature very quickly. (50-500ms depending on the lamp) Nevertheless, the “Peak Watts” demanded by a 100 Watt lamp would approach 1400 Watts, with a peak current exceeding 11.5A. For a 100 Watt lightbulb. And it all happens without anyone taking any notice.
Why does nobody notice any of these things? Perhaps because what someone wants from a lightbulb is a room filled with light. You screw it in and turn it on and you don’t have to go to school to have light in your room. The electrical wiring in your house just supplies the peak watts and the RMS Watts without arguing about whether the watts are “real”.
If there are things most people don’t know about powering a simple 100 Watt lightbulb, it’s very likely that there’s a lot more that a lot more people don’t know about the infinitely more complex process of amplifying audio signals and then converting them into physical energy for the sake playing music and it’s probably not appropriate to simplify everything involved down to a single metric, never mind a single number. So ask yourself, Watt’s wrong with doing that? -- David Lee