When a trumpet or trombone plays loudly - or a bass drum or gong is hit hard - the sound that is produced by the instrument is dynamically linear with the softer sounds that instrument can make. The same cannot generally be said about a loudspeaker that is reproducing those sounds.
Imagine for a moment the difference we might hear of an orchestra playing loudly in a small room vs. that same orchestra playing loudly outside - the differences between loud and soft in the first example would not be linear because the small room the orchestra is playing in would overload and compress those dynamics. This is fundamentally the same thing as what most loudspeakers will do when they try and reproduce large dynamic range swings.
What's interesting is that we don't have a means of measuring and calling attention to this form of compression in loudspeakers. Why? Because technically most loudspeakers are capable of reproducing without compression the full dynamic range found on most recorded music - and that IS something we can measure. What we don't measure is the strained sound or the 'apparent" compression one hears in such loudspeakers.
I don't know enough about all this to give you any hard facts. What I can share with you is my experience listening to many a loudspeakers system - and on most this change in character of the sound between the loudest and the softest passages is almost always evident on all but the biggest systems I know of.
Listen on yours to see what I mean. Note how the character of the instrument or voice changes when the presentation gets really loud vs. really soft. Some of this is most certainly your room but much of it is your loudspeaker - because on the biggest systems I know of (like the IRS and Gen 1's) this problem doesn't exist - even in a smaller room.