Those are great videos and you can easily notice the sound of the room just in comparison to each video you posted.  In the second video link (where he's talking in his studio) there is almost no room reflections at all.

IMO in cases where you rent or own a home that doesn't have a dedicated listening space there are so many trade offs that it becomes difficult to draw the line between room diffusers and furniture that makes the room interesting and/or cozy or comfortable.

For instance, I have a big mirror right behind my sofa which is also the sweet spot, I know that I should have diffusers there, but my girl loves that mirror and the way it makes our room look so much bigger and ties into out mid century sort of vibe we have going.  My first thought is to at least get a set of diffusers to flank each side of the mirror and then perhaps that may tame some reflections.

In a case like this one, the mirror is really no different from the drywall.

If you lean back on the couch, your head is so close to the wall that the reflection from that wall is not smearing the time.  If you lean forward then yea, having something to refract or scatter the sound off the wall would be a plus, but absorbing the sound would likely be even better.

A good test to find out would be to hang a moving blanket over the mirror that is spaced about 2 inches out from the glass.  Then listen a bit, then remove the blanket and re-listen to the same songs and repeat.


A more interesting test would be to listen without side reflections from the rear wall.  To do that, make a stick to hang the blanket on like you probably did for the last test, but bend the stick 90 degrees in the exact center.  Once again hang the blanket centered over the mirror.  You now have a blanket coming out just past your ears at a 45 degree angle on either side of your head.  I have a gut feeling this might be really interesting.

Steve

I like that last idea, Steve, very clever!