I was talking to another voice teacher (actually we were texting, but for introverts like us I think it counts as a conversation, haha) and she was asking me how I deal with young singers who have totally different qualities in their lower and upper registers. It almost sounds like they have two completely different voices. She mentioned that this seems to happen more often with her young altos and mezzos than sopranos. Does this sound like you? What to know how this happens and what to do about it? Then read on!
While this system is important to singing, I mainly want you to see where and how the larynx is situated to make the next picture make more sense. This is the top view of that larynx. Now you can look inside and see where your vocal folds are situated.
So you see that there are muscles inside your larynx as well. I've essentially isolated the thyroaretnoids (T.A.s) and cricothyroids (C.T.s) in my illustration because they're the muscles that are responsible for this sense of dual vocal quality. Essentially, the C.T.s control the pitches in your chest voice, that deep part of your voice where you feel sympathetic vibrations in your chest. By contracting and releasing, they manipulate your vocal folds so that they vibrate in different spots creating different pitches. The T.A.s on the other hand control your head voice, the high pitches that might feel buzzy in your skull rather than your chest.
Now, some pitches are only going to be able to be produced by either the CTs or the TAs because they're either really low or really high. But what about all of the pitches in between? That's where it can get kind of interesting. These pitches can be produced by multiple possible manipulations; you can either favor the TAs or CTs or employ a combined manipulation of both muscle pairs. When both the TAs and the CTs are working this is called "mixed voice." Some of these manipulation options are going be healthier than others.
So, what's making that "two voice" effect? Basically it's you switching from one muscle group to another (i.e. CTs to TAs and vice versa) as you vocalize. If you're untrained, it's probably easier to just pop back and forth between the muscle groups rather than gradually transitioning to the next muscle group. Think about doing a push up and lowering yourself slowly all the way to the ground. If your muscles are under-trained, you're not going to be able to lower gradually, you'll just plop on the ground. That's essentially what's happening to your voice.
Well then, how do you fix it? You fix it basically the same way you'd fix that push-up: by repetitive exercises. Generally I find that Sopranos/tenors favor their head voices and mezzos/bases their chest voices (although not always), but basically the way to fix it is the same--you may just work from different starting points. Here's what I'd do in a series of lessons:
First, I'd begin by working the voice in the less-comfortable range. This can be a little tricky, because I don't want to create tension, but the under-developed range of the voice needs to be worked out. So, I'd find a selection or two of short folk or other simple songs that are in that range. For a mezzo (or base/baritone) struggling with her head voice I might try "Love" from Robin Hood or "How Can I keep from Singing?". For a Soprano (or Tenor) who needs to work on her chest voice I'd pick something like "Are You Going to Scarborough Fair" or "Where are you going?" From Godspell. Maybe we'd just use sections of those pieces. I'd ensure those sections were tension-free and ask students to sing them every day. Often I have to reassure singers that it's okay for them to sound weak or young and remind them not to "force" a more mature sound. That sound will come as you work out your voice. It's really just the same as working out at the gym and gradually increasing your strength and endurance--if you force something too early you're asking for an injury.
Next, I'd run the student through a TON of slides. Something simple like this (sing these on an "ah"):
I'd work from a comfortable range gradually moving into newer territory, depending on the voice. The KEY with these exercises is to really slide. The tendency is to skip some pitches somewhere (especially towards the end of the slide) and again just sort of "plop" onto the next pitch. If you do that the exercises won't work. You have to really hit every little micro-tone in between the pitches. Move slowly enough at first that you are sure you haven't skipped anywhere. If your voice wants to "pop" somewhere, do it again, more slowly. Once these exercises are comfortable, I'd add various vowels, maybe even work some vowel equalization (see this blog post). I have several other vocalizes you can try in mymaterials section on the website.
Unlike my straw tool, this isn't a quick fix kind of thing (although running trough these exercises with the straw is a good way to avoid tension inyour less-comfortable range). It takes consistent, correct practice to meld the two voices into one. Just be patient with your voice and gradually build up the strength you need.