Right, because there is a Bright cap / high pass capacitor soldered to the back of a volume potentiometer, to pass highs but not bass & mids. you can put a second potentiometer between that capacitor and the wiper of that volume potentiometer to blend in how much high pass you want for bedroom settings or just any lower volume under about 7 you want. If you don't want to drill holes just put a resistor there. you could figure out what resistor you wanted there by putting a temporary potentiometer, find out where you like it and then measure that potentiometer and put the closest resistor to that value between the bright cap and the wiper of the volume control. another option is to put a switch with a couple of different resistors for different room settings.At low volume, it's actually not the high frequencies being loud, it's the bass and mid being low. When you turn up any sound, they become more prominent.
Marshalls are tuned as live amps, so they
sound their best loud and fighting in the frequency spectrum with the other instruments in a band.
Other amps, targeted towards the home market, where usually one plays at much lower volumes and alone, are tuned for that, so they have more mids and bass at a low volume.