An acoustic musical string instrument, such as a guitar, and related methods include one or more of 1) slanted sound posts extending between the front sound board and a lateral brace on the back plate of the guitar; 2) longitudinal braces extending between a lateral brace and a side wall of the guitar, 3) longitudinal blocks extending between adjacent lateral braces of the guitar, between a lateral brace and the neck block, or between a lateral brace and the tail block; and 4) a metal covered bridge plate.