Allan Colin's range building program is based on sound physiology. Gradually increase your range while ascending, and taking as much time in the low register to keep your embouchure supple and safe from lasting hard and overwork. It is a simple method, concisely written, that will give you huge gains without any risks. Here is what Allan says in the foreword:

“This method is designed to comfortably increase your range by alternating ascending (range building) exercises with descending (relaxa...