In addition to the points already made, an additional issue is that a room can sound brighter at higher volume levels!
I run into this all the time at audio shows where the rooms are hotel rooms that aren't built as well as rooms you might have in your house. At lower levels reflective surfaces such as windows and framed pictures might seem innocuous but if the room is driven too hard you might find it painful.
In a nutshell the room is at least 50% of the total system quality! I have lots of LPs and they have proven to be good room diffuser elements when neatly stored in their shelves (rather than stacked on the table beside by my turntable...). This is why there is a room treatment business.
One other thing that can affect tonality when the volume is increased is the effect of the volume control on the surrounding circuits. This usually affects tube preamps more than solid state. There is this thing called Miller Effect, which is the input capacitance of the amplifying device interacting with the outside world. It can affect frequency response! A classic example is a loss of high frequencies in the middle of the control (the impedance of the control interacts with the input capacitance of the tube or transistor) If you happen to use that part of the control a lot, turning it up past that point might make for more HF response.
This problem can be controlled by careful design.
I run into this all the time at audio shows where the rooms are hotel rooms that aren't built as well as rooms you might have in your house. At lower levels reflective surfaces such as windows and framed pictures might seem innocuous but if the room is driven too hard you might find it painful.
In a nutshell the room is at least 50% of the total system quality! I have lots of LPs and they have proven to be good room diffuser elements when neatly stored in their shelves (rather than stacked on the table beside by my turntable...). This is why there is a room treatment business.
One other thing that can affect tonality when the volume is increased is the effect of the volume control on the surrounding circuits. This usually affects tube preamps more than solid state. There is this thing called Miller Effect, which is the input capacitance of the amplifying device interacting with the outside world. It can affect frequency response! A classic example is a loss of high frequencies in the middle of the control (the impedance of the control interacts with the input capacitance of the tube or transistor) If you happen to use that part of the control a lot, turning it up past that point might make for more HF response.
This problem can be controlled by careful design.