What is mixed voice?
Mixed voice is a blending of the chest register with the head registers at a point where they share resonances of both registers. Blending chest resonance into head resonance is actually a very simple technique but difficult to master. The spacing between middle C and tenor high c is called the â€œbottleneck octave. It is called the bottleneck octave, because all singers encounter problems singing between these two notes. Why you may ask? Because all singers have to msing through one or two of their register breaks between these two notes. For male singers the first register break occurs at F#4 above middle C and again at A#4 below tenor High C. For females the first register break appears at A# below tenor high C.
In the typical male voice, mixed voice occurs at F# above middle C and carries through to the A below tenor high C. In the typical female voice, mixed voice occurs at around the D above tenor high C. In both places singers must employ the use of pharyngeal resonance to thin out the voice and blend it into the head register.
For each singer to avoid a falsetto like quality as they sing into the head register, they must apply more and more pharyngeal resonance to their sound. If pharyngeal resonance is not applied to their tone the voice becomes too hollow and hooty sounding. Rock singers want to avoid this hollow sound and go for a sound that has more of a metallic or edgy sound. By contracting the pharynx, upper harmonics are added to the singer's voice, thus creating a matching resonance to the chest register. The pharynx consists of three parts the laryngopharynx, the oropharynx, and the nasopharynx. The laryngopharynx is where chest resonance comes from, the oropharynx and nasopharynx aid in creating the metallic, edgy head resonance all Rock singers strives for.
Because the frequency becomes more rapid the higher ones sings the short waves pass through the ringed laryngopharynx and oropharynx without being applied until he reached the nasopharynx ray resonator can be found to match the faster frequency. In nthe middle of the octave between the two C's, which is approximately F sharp, the resonators should share the reinforcement of sound at about a 50-50 ratio coupling the laryngopharynx with the oropharynx plus the nasopharynx in this ratio. This is how blending the resonators of the chest register with the resonators of the head register creates a mixed sound. Most singers are unaware nof this principle. So they end up tightening the larynx or the pharyngeal muscles in an effort to squeeze a large resonator in the chest voice down to make the fast frequency of the high notes. When the proper resonator for the fast frequency is opened correctly by lowering the soft palette and pulling away from the back wall of the throat singer does not need to strain because he has a resonating cavity ready to adjust for the desired pitch. If a conscious effort is made to select the proper resonator, the necessary muscular adjustments within the larynx appear take place all by themselves. I have found most singers eliminate problems within their voice if they simply get out of its way. Far too often singers try too hard to sing, thereby bringing in more muscular movement and constriction than is needed for singing. With some very minor adjustments to a singer's technique, the voice is capable of many beautiful sounds without a lot of effort.
As a teacher I have found that all voices, male or female base or soprano and counted the greatest difficulties on exactly the same pitches i.e. over the octave from C4 to C5 (aka "the bottleneck octave"). Therefore, both singers male and female must apply mixed resonance in exactly the same way. To simply say to a singer "use both upper and lower resonances" is not clear enough to make the proper adjustment. One must hear an example to clearly get an understanding of how it is applied. A major part of the trouble in this critical range is created by the reflex action of the swallowing muscles, which most individuals use to some extent while speaking. Interference occurs, the instant the swallowing muscles are engaged, because they pull the larynx up against the nhyoid bone. The degree to which this pulling takes place determines the extent of the interference. There are just as many different incorrect combinations possible as there are correct combinations. The ability for the singer to keep the soft palate lowered at all times is critical in making a mixed resonance. A high palate restricts these shared resonances making them near impossible to achieve over the bottleneck octave.
Keeping the oropharynx and nasopharynx (the upper resonators) fully available at all times makes the resonance mixing and adjustments possible.