The manual mentions a couple of things that could account for excess bass, one being the Extra Bass button (X-Bass indicated on front); the other being the ROCK setting, which boosts bass.
http://www.retrevo.com/support/Sharp-XL-HP505-manual/id/285dj790/t/2/
Placement of the speakers relative to the room surfaces and the listening position can affect their perceived bass response. Experiment. Corners and close wall reinforce the bass, moving the speakers out from them would lessen it.
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