There seems to be a lot of misconceptions about what I am after here. By mentioning "in the room" sound, I don't mean that I want the room ambience into the sound. I mean the frequency spectrum itself. If you close mic the speaker from an inch away, you'll hear very different type of sound than in the room, because different parts of the speaker sound different. In the room you'll hear the whole speaker area, how it sounds as a whole. That is what I meant by saying "it is possible to actually hear that sound in the room".
Ah ok I think I see a misunderstanding here.
No, you won't hear the "whole speaker area" in the room.
Stand in the room and listen to a cab. After that, move your head a foot in any direction and listen again. Notice how the tone is
completely different now. So where exactly in the room is the "true" sound of the speaker? The answer is that there isn't one, because there is no "one true whole sound" of a speaker. A cab puts out an entire spectrum of different EQ+phase signatures depending on where you stand in the room relative to the cab, and will sound different depending on the characteristics of the room is as well. All a mic does is capture a specific one of these EQ+phase signatures in space, out of an entire spectrum of tones. In the room, your ears just capture two of these EQ+phase signatures from said spectrum, and your brain mixes them in stereo. You can do the same thing with two mics. Either way a mic setup close to the cab hears no more or less of the "whole speaker sound" than your ears.
Also, think about how much farther away from the speaker your head typically is than a mic. You're hearing a LOT more room reflections than you think. If the cab would sound different in an anechoeic chamber, then your ears are hearing a whole lot of the room mixed in with the speaker. Plus, your ears can't both face the cab at the same time, as they're on opposite sides of your head. In a room, you might hear
some small amount of vibrations directly caused by the speaker, but usually only in one ear at a time, and you hear just as much if not more room reflections bounced from objects or walls. And even if your head is on axis with the speaker, the speaker is likely way off axis from your ears, so does that mean your ears aren't perceiving the sound as truly as possible then?
There is no singular "in the room" tone. "In the room" tone is a myth. Instead there is an entire spectrum of sound any given guitar cab will produce throughout a given room, and where you put your head at any given moment dictates what you will hear, but that is by no means representative of the "true" tone of the whole speaker any more than what a mic would hear.
