On the leakage inductance in audio transformers

Leakage inductance is caused by that part of the primary flux that doesn't make it to the secondary. That, and the stray capacitance across the primary, limits the high-frequency performance of the transformer. Using a clever combination of split and overlapping windings, this can be optimized, but what is the best combination for a particular transformer? Pierre Touzelet has analyzed the situation. This article is heavy on math but the conclusions point to a set of rules that are surprisingly simple.