The Relationship between Loudness and Frequency
The image on the left is a glottal waveform, which represents the acoustic output of the larynx. The diagram is modifed from this website. The left side of the arc represents lateral movement of the vocal folds as they open. You can see that the more they open, the higher the volume of air that moves through the vocal folds. The right side of the arc is the medial movement, made as the vocal folds start to close. At the end of the medial movement, the vocal folds are closed and there is no air moving through the larynx.
The open time is the time that the vocal folds are open. In this diagram, the open time is the time of lateral and medial movement. Here, it is 4 + 3 = 7. The numbers here are in milliseconds (ms), so the open time is 7. We can see from the diagram that the vocal folds come back faster to the midline than they came apart. It took 4 ms for the vocal folds to become completely open, and 3 ms for them to close.
The T at the bottom of the picture represents the Total period, or complete cycle, of vocal fold movement. It includes the open quotient plus the time the folds are completely closed. Here, the Total period is 3 + 4 + 3 = 10 ms.
The open quotient (OQ) is a ratio expressed by the time the glottis is open divided by the total cycle. Here, the OQ is 7/10, or .7. This means the glottis is open 70% of the time of the entire cycle.
There is another relationship here, too, called the speed quotient. The speed quotient (SQ) is the time of abduction or lateral excursion of the vocal folds over the time of adduction or medial excursion, Here, SQ = 4/3. The speed quotient gives us information about the vibratory characteristics of the vocal folds.
You can see more pictures of glottal waveforms in your textbook, on page 84, figure 4.20. Look at the first picture in that figure and take the following quiz. The quiz is a matching quiz--match the numbers 1, 2, and 3 on the figure to what they actually represent.
Pitch and loudness tend to co-vary. That means that when pitch increases, loudness increases. It is easier to sing a high note loudly than softly because of the common factors of subglottal pressure: the influences of the larynx and the lungs. When subglottal pressure increases, pitch increases. When subglottal pressure increases, loudness increases. Pitch is primarily affected by laryngeal changes and secondarily affected by respiratory changes. Loudness is primarily affected by respiratory changes and secondarily affected by laryngeal changes.
We also know that if someone is phonating and is punched in the stomach, both loudness and pitch increase. Pitch increases because of two factors: 1) the reflexive tensing of the vocal folds, and 2) the increase in subglottal air pressure, which causes the vocal folds to adduct more quickly as a result of the heightened Bernouilli effect.
The increased vocal intensity results from a greater resistance by the vocal folds to increased airflow. The vocal folds are blown wider apart, releasing a larger puff of air that sets up a sound pressure wave of greater amplitude. The vocal folds are moving farther apart, but they also stay adducted for a larger part of the cycle.
You can see this graphically depicted if you look again at page 84, figure 4.20. The frequency in the bottom figure is greater, reprented by a greater number of peaks, and the peaks are higher. The height of the peaks represents intensity.
Now that you have learned about loudness, take the following quiz.