From the review, it looks like the solid internal brace blocks off "slightly more than the bottom half of the speaker." Rather than referring to it as a bookshelf, maybe standmount speaker is more apt? Who knows. Seems to have a good amount of internal volume to help with the frequency response.

That would be a pretty good comparison with the M50. Hmm, maybe we could talk one of the M50 owners to purchase one of the RS450s and do a review. . .

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