There are a number of different ways in which one can get a feeling for the voicing of sounds. Say 'zebra' with a very long [z] at the beginning: [zzzzzzibr´]. While you do this, hold a finger to your larynx and see if you can feel the vibration of the larynx. Then say 'sea' with a very long [s]: [ssssssi]. You should be able to feel with your finger that there is no similar vibration of the larynx during [s].
When people sing, or speak with high vs. low voice, they change the speed of vibration of the vocal cords. Fast vibration makes for a high voice, and slow vibration makes for a low voice. Try this with [n] first. This is a voiced sound. You can sing on [n] in a low voice, and in a high voice. Next, try this with [s]. If you make a voiceless [s], you will notice that there is no way of singing on this in a high voice or in a low voice. This is because the vocal cords are not vibrating during [s]. Therefore, they also cannot vibrate fast (for a high voice) or slow (for a low voice). They just aren't vibrating. Now contrast this with [z]. It may not be as simple as singing on [n], but you should be able to notice that it is possible to sing on [z] in a low voice, and in a high voice. Since this sound is voiced, the voice can be high (vibrations fast) or low (vibrations slow).
During speech production, we make noises of different kind. The noise produced by saying [n] comes entirely from the vibrations of the vocal folds. The noise receives its particular [n]-quality from the way the air passages in the vocal tract are shaped during this sound. Similarly, all vowels in English and German are voiced. The noise produced with any vowel also comes from the vibrations of the vocal cords, and receives its particular quality for each different vowel from the way the tongue and the lips are positioned during the vowel. A different kind of noise is produced in [s], which does not depend on the vibrations of the larynx. This sound, after all, is voiceless, but makes some noise nevertheless. However, much of the strength, or force of our voices during speech comes from the vibrations of the vocal folds during articulation. You can get a sense of this by saying a few words aloud first, and then whispering them. What you do when you whisper is this: your vocal cords do not vibrate. Instead, they are positioned so as to produce a weak kind of hissing. Otherwise, everything else is the same between whispering and saying things normally. When you compare whispering to speaking normally, you can see how a lot of the noise produced by speaking really comes from the vibrations of the vocal cords, which is absent during whispering. Try this now.
This is true even more when you shout to someone far away. When you shout, you produce more forceful voicing with the vocal cords. Can you shout while whispering? A little bit, but it doesn't carry very far.
vocal cords, also vocal folds [G. Stimmbänder]: two muscular folds inside of the larynx. They are attached to particular cartilages [G. Knorpel] of the larynx, and can be positioned, and can also be made stiff or slack. When they vibrate, they produce what we call voicing. In that case, they are held together, and are slack. The air pushing through them from the lungs sets them in vibration.
glottis [G. Glottis]: the area between the two vocal cords.
4 The soft palate and the airflow through the nose
After having discussed the larynx, where trachea and esophagus come together, let us turn to the point where the channel through the nose separates from the channel through the mouth. We saw earlier that this is the position of the soft palate. The soft palate is muscular tissue and can be moved. Importantly for speech articulation: It can be raised in such a way that it closes off the nasal tract. This is shown in Figure 4. The picture on the left shows the soft palate in a position in which it is not raised. Here the air that comes up from the lungs through the larynx (with or without vibration of the vocal cords) and can pass through the nasal tract. The picture on the right shows the soft palate in a position in which it is raised. Here the air cannot flow through the nasal tract. In this case, the air that is pushed up by the lungs may or may not escape through the mouth (the oral cavity), depending on the position of the lips and the tongue in the mouth.
To get a bit of a feeling for the two different positions of the soft palate, say the sequence [dndndndn...]. During this sequence, your tongue is closing off the airflow in the mouth entirely, and the tongue does this in the same position for [d] and for [n]. So the tongue doesn't move. However, the soft palate moves: During [n] the soft palate is not raised, so the air comes out of your nose; during [d], the soft palate is raised, and the air cannot come out of your nose. The only thing that moves during the sequence is the soft palate, alternately closing off nasal airflow and making nasal airflow possible again. Can you feel this in the back of your mouth? If you are like me, you can't feel it much. Perhaps this little exercise is really for showing how it is difficult to have a good feeling for the soft palate. However, this is as close as we can get.