I used to set sub size and other config via the front panel of my G61. When I got to the subwoofer size I gradually increased the sub test tone (not to be confused with the test tone used for balancing the sound level along with the other speakers - it's a separate sub size test tone) from 0 to max and listened for any distortion as the level went up.

The idea was to get to the point of obvious distortion, then back it down a little for safety. My analogue sub handled max with no problem, others may not. Obviously, having it set lower than necessary can result in losing some bass at times, when you don't need to.

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