Originally Posted by joegreen
Let's say an car stereo amplifier is 50w rms. When I turn on the radio does the amplifier always deliver 50w to the speakers or does it deliver 0 to 50w linearly depending on whether the volume knob is at a minimum or maximum?
Not quite linearly, but on a curve approximating human hearing sensitivity, and not always delivering 50W, only outputting based on the signal level multiplied by the gain of the amp.
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Also does the amplifier amplify the power it's being fed?
Sort of. Any separate power amp is going to boost the vehicle 12V system to give it enough rail-to-rail headroom to amplify the audio signal by the amount of the gain set. For example if you have a line level input signal of 1V and a gain of 20, it will have to have 20V to work with to get that done or else it'll clip trying to. Really it needs a little more than 20V because of voltage drops in the process. 20V is just an example, most amps boost the power rails to higher voltage than that.
So, it boots the input voltage, then modulates that voltage to produce the AC output mirroring the input signal. Any voltage above and beyond what it needs to reproduce that signal is not used. In a class A amp that is very lossy, somewhat lossy at lower volume on a class A/B but for a typical class D amp it is pretty efficient.
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An example would be the stock head unit supplying 10w to the amplifier and the amplifier amplifying the voltage an additional 50w for a total of 60w delivered to the speakers.
What a stock head unit can produce is only relevant powering a load, the speaker(s). The amp uses a low level input whether it is already low level at the input to the amp or whether it uses a method of reducing the input signal to that level (often just a resistive voltage divider). So, the head unit may be able to supply 10W but the amp is not consuming that wattage, rather a small fraction of a watt.
No, these two values, input wattage and amp wattage do not add together. The amp wattage alone is the maximum output and even that, typically at a very high THD distortion that you won't want to be anywhere near for how bad it sounds.
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Or does it not matter how much wattage is delivered to the amplifier it will only ever output a max of 50w to the speakers even if say 60w is being inputted into it?
See above, there is never 60W truly input and consumed even if the head unit would've been capable of and been delivering that if it were a speaker attached instead of the amp.
It might have been easier to get to the result you want by stating what parts you are using (or still need to select) and what the intended result is. I am not a fan of deafeningly loud music, but I also wouldn't bother putting a mere 50W amp into service unless it is just to power a small sub or to repair a failed factory audio system that had adequate loudness already. Unless it's some boutique audiophile brand, low powered amps tend to have more corners cut than just their output wattage in order to arrive at a low price point, although if it is rated at only 50W, at least it is probably closer to honestly rated instead of the fictional high wattage claims that some dubious manufacturers make.