PH, welcome back. Yes, the internal volume of the on-wall speaker is only about half that of the standard M22. So, the enclosure is tuned at a significantly higher bass frequency. The size of the enclosure, other factors being equal, has no effect above the bass range. Coupled with a good sub and crossed over above say 80Hz, there should be little or no overall difference in sound.

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Enjoy the music, not the equipment.