Proportioned by phi

The body length and the lower bout are the foundational dimensions. From those two numbers, the golden ratio fixes the position of the waist measured from the neck joint, and then the positions of the upper and lower bouts in turn.

The waist width follows the same ratio, cross-checked against the performance parameters published by Trevor Gore in his book “Contemporary Acoustic Guitar Design and Build”; the upper bout width is derived from the golden ratio of the difference between the lower bout and the waist. The consequence is that the relationship holds across the whole outline rather than at a single point.

Two quantities are in the golden ratio when the ratio of the larger to the smaller equals the ratio of their sum to the larger. φ is irrational, approximately 1.6180339887.