Since you are removing some wood with the chamfer doesn't that compromise the strength of the corner?
Or are you compensating by adding a corner block on the inside?
I'm not the builder, Oskar, but I can tell you that strength of the
corner is dictated by the material itself in this case. The glue joint, the strongest part of a butt joint, remains fully intact from what I see. I'd have no concerns doing what's illustrated if the joint itself was sound. If the structure didn't have bracing elsewhere, and you were to do apply diagonal pressure corner to corner, I can see the strength being compromised by the reduced thickness at the corner, but this is a speaker box after all and there are shelf braces resisting that sheer force. One could add corner blocks but considering all else it would seem superfluous.
The notion that this would affect the performance of the speaker somehow just doesn't hold water, IMHO. Here's a cross-section graphic to help illustrate my point.
EDIT: I realized my illustration was wrong. I corrected it to show approximately 5/8" across the face of chamfer and 5/8 radius. Mo betta now.
