The site for this event is the University of Groningen, the Netherlands, where Janwillem van den Berg formulated the myoelastic-aerodynamic theory of voice production nearly 45 years ago. Not long thereafter, with William Vennard, he began a tradition of research on the singing voice that has continued there unbroken to the present day.
Prof.dr. Janwillem van den Berg. (20 November 1920 – 18 October 1985)
Personal impressions from the career of a great scientist.
During World War II Janwillem van den Berg took shelter in Groningen from the Germans in order to avoid possible transportation to Germany as a war worker.
The son of a butcher, he was born in Akkrum and went to Amsterdam to study physics. There he came into contact with the current explanations of how the voice organ worked, as taught by Prof. Louise Kaiser, the first professor in phonetics in Amsterdam, originally trained as a medical doctor.
Van den Berg’s training as a physicist made him doubtful of the then-current explanation that the voice worked on the same basis as Savart’s explanation of the Hunting Whistle. His intuition told him that this could not be true, and he designed experiments to verify or falsify the hypothesis.
Settling down after finishing his training -- mainly as a mathematician -- as a physicist in Amsterdam, he got a position in the Physiologic Laboratory, where he had an opportunity to perform these experiments. The results were described in his thesis in 1953.
His thesis dealt with other issues of voice production as well. In those years the French physicist Husson had developed an alternative theory to explain the vibrations of the vocal folds, the neurochronaxic theory. A further topic was vowel production. Chiba had just published his monograph "The Vowel" in 1941. Not much experimental data was available at that time. Van den Berg’s thesis experimentally addressed the function of the vocal tract in a semi-laryngectomised patient with a neck fistula. Via this neck fistula the vocal tract could be stimulated acoustically with a specially designed loudspeaker.
In separate chapters Van den Berg addressed the important issues of that time:
1) voice production, with a re-evaluation of the literature on this subject (and as he wrote in this Chapter 2:) "This Chapter gives an elaborate and as we believe a balanced and physically funded theory of voice production. As to the framework this chapter has the character of a monography. In building up the theory we use the results of our own investigations which are mainly described in the following chapters, and data from the German, Anglo-Saxon, Japanese, Dutch and French literature, which are critically discussed".
2) The topic of current interest – in those days -- was to understand the production of vowels, the essentials behind this production, and then way this knowledge could be used to reduce the bandwidth of a signal to get enough signal transmitted in parallel: 3) A chapter written partly in French – in a Dutch language thesis to refute - Husson’s neurochronaxic theory.
The promotion on June 18, 1953 was rewarded with a cum laude, and the day after the thesis defense he married.
Many foreign colleagues regretted that the thesis was written in Dutch, and some of them even started to study Dutch to be able to read it. At least one full translation of Chapter 2 is known in English, the voice production overview.
As can be seen from the list of publications on voice-related topics, many articles were written on topics already mentioned in the thesis. Other publications, like the frequently cited "On the air resistance…", were based on new experiments. Due to the lack of information about the acoustical aspects of the lungs, trachea and bronchial system, work was initiated to simulate the bronchial system with an electrical analogue. The close co-operation with the department of lung diseases, e.g., in studying lung mechanics, led to a fundamental understanding of the relation between the pressure in the esophagus, measured with an esophageal balloon, and the lung volume. (It would be interesting to study what caused the error in Van den Berg’s estimation of the first resonance of the subglottal system – about 300 Hz – where later experimental results showed a first resonance of about 600 Hz.) Knowing the relation between these factors led to the article: Direct and Indirect Determination… of 1956 and the first notion of efficiency of the voice generator. This work was continued more than 15 years later in the thesis of Schutte: The Efficiency of Voice Production in 1980. In this the concept of efficiency was applied to patients with different voice disorders and a large control group of "normals" (see Schutte).
Myoelastic-Aerodynamic theory of voice production
Based on the knowledge gathered for the thesis and the ongoing additional experiments, Van den Berg (re)formulated the myoelastic-aerodynamic theory as published in 1958. In these years he became interested in the experiment of Müller of the mid-19th century and repeated the experiments, carried out by an ENT-resident Tan. The results were published in Practica Oto-Rhino-Laryngologica 1959.
In 1958 Van den Berg was appointed Assistant-Professor, and in 1961 he got a chair in Medical Physics at the University of Groningen. He then founded his own Laboratory of Medical Physics, distinct from the Physiology Departments.
In the fifties vacuum tubes had been developed to a reliable stage, and they became commonly in use for constructing instruments for experiments and diagnostic instrumentation.
High speed filming on the vocal folds was already done before World War II (Bell Company), but that equipment was complicated and very expensive. Of course, Van den Berg had interest in visualization of vocal fold movement, and he used the newly available flash tubes (up to 80-100 Hz) to design a stroboscope that was triggered by a throat microphone. He designed the delta-f generator to get reliable images of the (illusory) slowly moving vocal folds. This was incorporated in a commercially available stroboscope.
The images obtained with this stroboscope appeared to be a good alternative for the high-speed imaging of the vocal folds. Van den Berg often showed a comparison between stroboscopic images with delta-f generator and parts of the Bell film. This was the main reason for dropping his plan to buy a high-speed film camera around 1960.
Esophageal voice physiology
Van den Berg immediately saw practical applications of new techniques in medicine. In the beginning of the fifties he used the newly developed X-ray image intensifier technique to study the dynamic physiological processes in the so-called injection method for the speech rehabilitation after laryngectomy. The knowledge gathered was published in one of the very best articles on the physiology of esophageal voice.
This study brought together all the knowledge on the air pressure behavior in the esophagus during three different thoracic acts: 1) breathing, 2) laryngeal phonation and 3) substitute voice production.
In 1960 an excellent instructional film was published with the cooperation of the singer William Vennard and two co-workers: Shervanian – who visited Van den Berg as a Fulbright scholar, and Deis Burger, an ENT resident from the University Hospital in Groningen. In those days there was a close cooperation between the Laboratory of Medical Physics and the ENT clinic.
This instructional film made him known all over the world, but it also marked a kind of end of the era in which voice research was primary for him. He then became responsible for teaching all aspects of medical physics. He wrote an immense number of treatises in Dutch on fundamental knowledge of physics, considered necessary for the medical doctor in those days.
A few examples of these are the following: -how to aid the breathing of patients with Poliomyelitis, -how to do safely a coagulation of brain tissue in the case of Parkinson’s disease, fundamentally not different from using laser nowadays, -a simulation of the peripheral circulation, in a thesis written by De Pater to understand and interpret the plethysmographic signals registered at the fingertip.
Blood circulation was also related to another important field of study – cardiac pacing. Van den Berg designed the first implantable pacemaker that could be switched to a higher beat rate for a higher level of activity. The first experiments for an R-top triggered pacemaker were done, and the design of electrodes to the heart was tested in animal experiments. This made Van den Berg known to the cardiologists of that time, and the fourth International Symposium on Cardiac Pacing was organized in Groningen in 1973.
Nasality and Spectrum
Much effort and time was spent exploring nasality via acoustical spectrographic recordings with the Kay Sonagraph. Hundreds of registrations of 2.4s were stored in large folders and attempts were made to correlate the spectrograms with clinical findings in nasality patients.
In the beginning of the sixties Van den Berg planned to continue research on the influence of the subglottal resonance’s on the vibratory pattern of the vocal folds. A co-worker was employed to build a new, more-refined set-up for excised larynges studies. In this set-up the acoustical properties of the subglottal system were to have been integrated. Experiments were carried out on dogs to study the influence of internal size of the lung airways and the influence of secretions in the lungs on damping of the resonances. There were plans to study directly the acoustical pressure waves, but at that time appropriate pressure transducers were not available. This was of course a continuation of the interest in the direct measurement of the subglottal pressures of the 1956 article, at which time only mean pressure values could be measured. His interest in the acoustical functioning of the vocal tract continued in using the sweep-tone procedure with external excitation of the vocal tract.
The narrator (HKS) of this biographical note became involved in all this as a medical student from 1963 on. The interest of Van den Berg in the air flow dynamics of the lung airways and the noise that was generated by turbulence stimulated his interest in the commonly used stethoscope. I got the task to study the acoustics of the stethoscope, about which not much was known. I learned the acoustical behavior of tubes of different lengths, internal sizes and wall stiffness. The proper equipment was brought together, but the topic could not be explored fast enough for a temporary student-employee, who, incidentally, also participated in the dog-lungs-acoustics experiments and the vocal tract-acoustic neck vibrator experiments.
As a medical doctor in the beginning of the 70’s, I became Van den Berg’s new co-worker on his "old-love – the voice". The experimental work was done in the ENT clinic of the University Hospital.
Van den Berg was very skeptical about electroglottography (see his 1962 main reports on Experimental Phoniatrics), but was highly interested in the air flow measurements initiated by Isshiki and Koike, in the Los Angeles Laboratory of Van Leden.
I was interested in applying the new concept of the phonetogram, and in using electroglottography. But in 1972 Van den Berg convinced me that the way to go was to make simultaneous measurements of subglottal pressure and airflow rate, in relation to the sound produced, thus measuring the efficiency of voice production in patients. And since there were no normative data on this, a non-patient control group would also be measured.
The thesis was finished in 1980. I remember well the fortnightly meetings of two hours over a period of eight years, discussing the measuring procedure and interpreting the results. I am greatly indebted to the guiding force and scholarship of my teacher.
Already in the sixties people from all over the world came to visit Van den Berg. In the sixties I met Van Michel, developer of the first commercially available electroglottograph, Osamu Fujimura, James Stark, Isshiki in the late seventies, Richard Miller in the seventies, Svend Smith and Donald Miller in the beginning eighties. James Stark was the first professional singer of which the efficiency was measured for my thesis work. We established very high pressures. Van den Berg immediately organized a registration with a plethysmography of the finger tip while the subject sang a sustained, loud, high-pitched tone.
In 1977/78 Richard Miller came to visit Van den Berg and although Van den Berg was at that time involved in a lot of other experiments he guided us in two weeks of intensive cooperation. We stayed quite busy making aerodynamic measurements, tomographic X-ray pictures of the larynx, spectrographic measurements over the whole singing range, and registering the strength of the singer’s formant. We also recorded voice range profiles with different types of "registration".
After the thesis was finished in 1980, a new impulse came in 1983/1984 with the visit of Don Miller. Van den Berg saw the possibility of studying directly the subglottal pressure and its high-frequency components by using miniature pressure transducers that had recently become available. (They were also developed for studying the function of the bladder and the constrictor function to the urethra, and that was the type we used.) Van den Berg’s own experience of the experiments for the 1956 study convinced him that a carefully executed procedure would be feasible. Koike and Kitzing had already done similar experiments at that time. We also registered simultaneously the EGG-signal, which turned out to be an essential help in interpreting the signal.
Special amplifiers were made in the electronic workshop of the laboratory for medical physics. A registration procedure was developed of high-speed recordings, together with slow-speed recordings on paper of selected parts with proper calibration. The first results were extensively discussed, and we had to convince Van den Berg of the proper interpretation of the electroglottography signal. For some interpretations he remained skeptical, e.g., the resonance frequencies of the subglottal system.
We did not discuss enough in these years. Van den Berg retired from the Groningen University in 1984 and unfortunately died unexpectedly after one week of hospitalization, on October 18, 1985.
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