If you think vibrato is a maelstrom of controversy, batten down the hatches for registers.
Virtually every book we read on singing, whether by singers, teachers or laryngologists tends to describe registers in different ways - how many there are, where they merge and how broad is the merging zone - usually known as the passaggio. Also, there is a lot of confusion regarding nomenclature. What, for instance, is the difference between head voice, head tone and head register? Well, I have my views - but so does everybody else and they don't necessarily converge! In my experience, it's best to leave it to nature. But I will nail my colours to the mast in stating that there are basically two registers - chest and head. The sensations of vibration in the lower part of the instrument are predominantly in the chest and the upper part in the head. But there's also a portion of the range in the middle that seems to be neither one nor the other. This is sometimes referred to as the mixed voice, sometimes the passaggio and sometimes the middle register. Yes, more confusion......
I therefore demur at spelling out yet another approach to register management. There are so many pitfalls and so many subtle and nuanced physiological changes, that guidance is paramount for the uninitiated or confused. So with that guidance, it's best to let the student find out for him or herself where these physiological changes occur - acknowledge them, get used to them and allow the instrument to develop around them without interference. Preconceived notions can upset these fine-tuned adjustments.
Pavarotti was not only a wonderful singer with a mastery of registers, but also a warm, friendly, fun-loving human being. © 2033 from Getty Images