I recently just tuned my gain to the specified VAC and was wondering why when I turn my volume up past my specified "max" volume on my headunit the sub gets louder?
I tuned it to 44.7 VAC since its 500x4 ohm so sqrt is 44.7. So I decided to test what VAC are coming out with my normal songs, and I got no more than 37 VAC.. ? What gives? I used a 50hz test tone.
Basically the Sub sounds better and louder at volume higher than what I tuned it for. Also why does Pandora and internet radio seem to play less loud?
Forty Hertz is the best tone to use but 50 will work. This is because most music has a lot of bass information in the 40Hz range and that's where clipping can get nasty. You can't see clipping with a meter though so it's really a moot point.
As for your other questions... music is dynamic, meaning that it isn't always at X amount of signal. Think of a song with short & silent passages and then other hard hitting passages. When the song is quiet, there isn't much voltage going to the amp so there isn't much coming out. Likewise, when there is a hard hitting passage, voltage increases and so does the volume. In simple terms, music is just a variable voltage/current signal as far as your audio system is concerned. For all it knows, a bass drum is a whale call is a sine wave... it's all just electricity. Also, if you try to measure signal levels with a volt meter (especially a slow digital one) you won't see the peaks or valleys of the voltages because they happen so quickly and are so short. What you will see with your meter is just an average of the signal level.
Last, internet radio, AM/FM and aux will always be more quiet than CD or USB because of exactly what I talked about above... voltage. The signal levels on those sources is lower than CD/USB signals so it will take a little more gain from your head unit volume control to make them as loud. That's not a problem but just keep in mind that if you go too high on the head unit volume you will be clipping the signal and that will happen before you can hear it. Normally, too high on an aftermarket head unit is >50% if using the internal amp for the highs and >85% if using external amp.
gain doesn't limit the output of the amp, it tells the amp how much to amplify the signal. Thus, if you keep adding voltage to the preamp signal (turning the volume up) the amp's output will keep rising... obviously, there is a limit to how loud the amp will play but that's not controlled by gain, it's controlled by other factors and the amp's internals.
