There is one other thing that no one has mentioned here, other than the resonances. How can you tell what your recording REALLY sounds like if the ROOM alters your perception of what you hear everytime you playback the recording. Let alone when you record. There are three things at play here.
At least, this is the theory as I understand it.
One. If you have a seperate control room from the studio, unless you have a TIME DELAY GAP(TDG)in the control room longer than in the studio, your perception of comb filtering or reflections in the studio will be masked, which affects your mixing choices. Usually, this is caused by early reflections from the front and side walls, ceiling and console face, which mask the studio TDG( comb filtering at the engineering position will affect what you THINK you are hearing in the monitors.) This TDG in the control room is created by treating these areas whereby the engineering position is in a REFLECTION FREE ZONE. This also implies, that a reflection from the rear wall must be at least 3ms longer than any reflection in the studio in order to hear it as the mind will integrate all sounds arriving at the ears within 2ms of the direct sound. If your rear wall doesn't allow for a minimum round trip time delay of 3ms, then you might as well treat it to absorb.
Two, if you record in the same room as you play in, then you CAN"T monitor the recording itself simultaneously on the studio monitors. That means you only have the recording itself to tell you what is on the media. If the existing room acoustics ALTERS your perception of the recording, then you have NO idea what it will translate to other rooms like. In other words, if you EQ according to what the room tells you, your choices will not be correct, because everytime you do, the room STILL lies to you.
Three, specular reflections from the rear wall may have extreme comb filtering. If this distance from engineering position to the rear wall allows for a 3ms delay, then diffusive elements should be added for a smooth RT-60 decay, although some claim there is very little proof of a diffuse sound field in small rooms. Although, I've seen "professional" test result illustrations of these decays. Whether or not this is current control room dogma, I don't know. What I do know is these problems remain the main culprets of control room monitoring. However, these are in addition and to the resonance/standing wave problems, at least from my understanding.
I'm certainly no expert, but this is what I've read by authors who are. Whether or not this is current train of thought is of no consequence, as the realities are the same, regardless. How you interpret it or treat it is up to you. Some may argue and dispute this. So be it. Enlighten me further so I can update my understanding of The Master Handbook of Acoustics and current control room design dogma, as it changes yearly.
fitZ
Sorry for russling feathers, but there's a variety of ways to do research when insulating and building a room.