We hear people talk about the vocal registers all the time. They throw around terms like headvoice, falsetto, chest voice, covered voice etc. Many times these terms are used to describe completely different sounds. Some people use the term falsetto when someone is actually singing in headvoice. So in an attempt to clear up the confusion I will give an accurate definition of all these terms.
Falsetto: I have written about this in a previous blog so I will make it short and simple. Falsetto is the sound that is made when only the edges of the vocal folds are vibrating. The main body of the vocal folds is inactive. The muscles that makes up the body of the vocal folds are called the thyroarytenoid muscles. These muscles are completely inactive in pure falsetto. In falsetto the pitch changes due to the pulling of the cricothyroid muscle which stretches the vocal folds, thinning them out. There are very few overtones produced in this register - only two overtones at most.
Chest voice is a sound that is made when the thryoarytenoid muscles (which makes up the body of the vocal folds) are fully engaged. The cricothyroid muscle is also still engaged, but the thyroarytenoids are more active than the CT's. The sound is much heavier and has many more overtones. So the thing to remember with chest voice is that the TA's are dominant. The vocal folds are shortened in this register.
Headvoice is a sound that is made when the thyroarytenoid muscles and the cricothyroid muscle are all active, but in this register the cricothyroid muscle is dominant. In the headvoice register the vocal folds are thinner than in chest voice register. The sound is therefore "lighter" than the sound of chest voice and it produces less overtones than chest voice.
From these definitions we can see that the main difference between how a man sings compared to how a woman sings - in classical music - is that a man sings thyroarytenoid dominant (chest) most of the time while a woman sings cricothyroid dominant (headvoice) most of the time. That is not to say that woman do not sing in chest and men do not sing in headvoice. To the contrary, women must sing in chest on their lower notes to be heard and men will sing in headvoice when they sing quietly. The chest voice range of a woman singing in classical music should extend past her passaggio. The passaggio is usually around E4 to F#4 depending on the voice. On the other hand, men keep full chest all the way up and down the scale unless the are singing quietly. This demands another muscular switch in a man's passaggio which is called "covering". A man's passaggio can be anywhere from Eb4 to F#4. Falsetto is really used just for training as it develops the full lengthening of the vocal folds.
Additionally, within these main categories for the vocal registers there are some other terms that need defining. These terms are "covering" for men and "coordinated chest" for women.
Covering happens as a result of the male voice needing to keep a thryoarytenoid dominant sound (chest) all the way up through the passaggio and into his high notes. Covering is a muscular switch that happens which allows men to achieve this. As a man reaches the passaggio he has to make this muscular switch to ensure that his larynx stays in a lower position while the TA dominates. The cricothyroids do become more and more active, but the sound stays TA dominant (chest dominant). So physiologically what happens is in the passaggio the CT's work more while the stylohyoid muscle as well as the infrahyoid muscles are engaged so as to keep the larynx stable in a low to mid low position. If they did not engage the larynx would either rise, giving a strangled sound that lacks any scuro (depth/darkness) or the larynx would drop down too far and the hyoid bone would push onto the thyroid cartilage giving an overly dark, woofy sound.
Coordinated chest in a woman's voice happens when she is singing in headvoice and adds as much chest participation as she can (thyroaryetnoid) while still remaining in headvoice. In other words, if a woman were to add too much TA participation she would go into chest or covered chest where the TA is dominating. Instead, coordinated chest adds as much TA as possible without becoming chest, but rather staying in a CT dominant sound. Less of the vocal fold vibrates than in chest of covered chest, but in comparison to headvoice, more of the vocal fold is vibrating.
Some of the confusion with these terms is due to using the word "coordinated". Technically any sound that is coordinated has both CT and TA working together correctly. An uncoordinated chest sound mainly only has TA active. Falsetto is also not a coordinated sound as it only has CT active. And both of these registers are used for training purposes. Once both registers are strong and balanced then you can "coordinate" them together.
I hope this post help clear up any confusion people have.