The so-called scientific approach to singing has been put down or dismissed as irrelevant or unworkable and yet the greatest teachers of voice of all time spent years researching the very sciences of the voice. Anatomy, medical science, physics, acoustics and other sciences all play a role in the understanding of the production of the voice. Things are not necessarily “black or white”. There are shades of differences which span a near infinite scale of that which is optimum all the way down to that which is destructive. Knowing more about the anatomy and the safeguarding of the human voice has come about from research done by several fields of science and the arts.
What is universal and what is individual has much to do with the success of learning from a book or course versus learning from a teacher who is with you and guiding you to be your best and doing so by working with you as an individual, rather than as a statistic or a category.
Vocal ranges, for instance, overlap and depending upon the level of development of the voice, the useful range can vary from one tenor to another tenor. The same is true with other “vocal categories“: sopranos, mezzo sopranos, altos, baritones, and basses. Just as there is a best route for a specific mode of transportation, there is also a best way of navigating the passageway between “chest voice” and “low middle voice”. The same is true for low middle to high middle voices, high middle to head voice, etc.
Some singers do not even have a developed or usable middle voice and instead have a “break” or “crack” or a “glottal stroke”. There are reasons that inconsistencies in tone quality exist and there are solutions to the same.
It is a great benefit to have a person (who is experienced) listening to you as you sing to help guide you through the passageways and to also assign exercises which help with coordination and strength to be able to connect all the vocal registers into a seamless usable voice that sounds like one voice rather than two or three or more. Some people do have multiple “breaks” in their voices. With training and practice these breaks “go away”. Simply knowing how to achieve a great singing voice, unless the singer practices diligently any more than anyone else who has achieved greatness has done so without putting in the time and effort of mastering specific sets of skills.