Yes, it's just the room. The size and shape of the room can cause some of the lower frequencies to bunch up, per se. So, you may hear a difference in the output in different parts of the room. Normally we all try to calibrate to the sweet spot, or the main chair you're going to do most of your listening from.

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"Nothin' up my sleeve. . ." --Bullwinkle J. Moose