Acoustical evaluation of historic wind instruments D. M. Campbell School of Physics, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, U.K, e-mail: [email protected] The later decades of the twentieth century saw a remarkable revival in the use of wind instruments of pre- modern design in historically informed performances of Renaissance, Baroque, Classical and Romantic music. In some cases surviving historic instruments have been available, but more frequently museum spec- imens have been carefully measured and reproduced for peformance. This process raises many questions; for example, original reeds and mouthpieces are often missing, and curators are increasingly unwilling to permit playing tests and invasive mechanical measurements of rare and fragile instruments. This paper sur- veys the use of acoustical techniques to study original instruments, to model their playing behaviour, and to guide manufacturers in the creation of musically excellent reproductions. 1 Introduction the assumption that a carefully made replica should re- produce not only the physical shape but also the acousti- The acoustical study of a musical instrument of any genre cal behaviour of the original. Further questions are raised or period can yield valuable information about its phys- by study of these replicas. Are the originals typical of ical and musical properties. In recent years, signal pro- their period? Should perceived acoustical faults be cor- cessing techniques of increasing sophistication have been rected in reproductions designed for performance, or are applied to analyse the sound output of the played instru- they part of the historic character of the instrument con- ment, while mechanical and acoustical excitation meth- cerned? ods have been used to determine the linear response of This paper reviews some of the ways in which the meth- the resonators in the instrument. The non-linear sound ods of musical acoustics have been adapted to meet the generation systems which are at the heart of bowed and specific challenges of working on historic wind instru- blown instruments have been investigated using a variety ments. Rather than attempting a comprehensive cover- of experimental and numerical modelling approaches. age of a very extensive field, the review focuses on a The study of historic instruments using acoustical tech- number of specific examples. Section 2 outlines various niques raises a number of specific issues. In this con- approaches to the problems of understanding the acous- text, the term “historic” is used to describe a musical in- tics of prehistoric flutes and horns, Section 3 surveys a strument which is either no longer manufactured in the number of pioneering studies of Renaissance wind in- form considered, or is made as a conscious replica of struments, and Section 4 offers a brief summary of some an instrument of a previous time (“period reproduction”). acoustical studies of the rapid evolution of wind instru- This description thus covers a very wide range of differ- ments through the Baroque, Classical and Romantic pe- ent types of instrument. Some instruments, such as the riods. sixteenth century Phagotum, survive only through illus- trations and/or written descriptions, while many prehis- toric instruments exist only in broken and fragmentary 2 Prehistoric Wind Instruments forms. Musical instrument museums contain numerous examples of instruments from the Renaissance onwards 2.1 Reindeer phalanx whistles which are more or less complete structurally, but which often lack crucial adjuncts such as woodwind reeds or Among the earliest wind instruments to have been studied brass instrument mouthpieces. In addition, the conserva- acoustically are the whistles made from reindeer phalanx tion policy of most museums now prohibits the playing of bones by the people of the Palaeolithic era. These have fragile wind instruments because of the danger of crack- been discussed in detail by Michel Dauvois and Benoit ing or other physical damage. Fabre [1]. One of the principal predators of the reindeer In the last few decades of the twentieth century, many in this era was the wolf, and many reindeer phalanx bones museum specimens of historic wind instruments were have been found with indentations and irregular holes physically measured, and reproductions were made to be probably caused by the teeth of wolves. In a number of played in “historically informed” performances of music surviving bones, a hole near the upper end of the phalanx ranging from the Middle Ages to the nineteenth century. has been carefully extended and made more regular, ap- These reproductions have provided one approach to the parently by human hands (Figure 1, right). When a jet of acoustical investigation of the original instruments, on air is blown across the hole by a player, resting the lower 369 Forum Acusticum 2005 Budapest Campbell Figure 1: Reindeer phalanx whistle. Left: reproduction; right: original. Photograph: Michel Dauvois [1] Figure 3: Spectrogram of a note played on the Reindeer phalanx whistle [1] lip in the indented end of the phalanx as though it were the embouchure plate on a modern flute, a piercing whis- The first admittance maximum, at around 2 kHz, is the tle is produced. Dauvois and Fabre have suggested that frequency at which the self-sustained oscillation excited this is the earliest evidence of a human sound production by an air jet would be expected. Sounding the instrument device. does indeed yield a frequency in the vicinity of 2 kHz, to- gether with some relatively feeble upper harmonics aris- ing from the non-linear nature of the jet excitation mech- anism, as can be seen in the spectrogram in Figure 3. In addition, the turbulent nature of the jet generates a broad- band noise, which appears in the spectrogram filtered by the (inharmonic) resonances of the cavity. One further aspect of the spectrogram should be re- marked upon. When a historic instrument can be played, either in its original form or as a replica, it is possible for the player to determine by experiment whether specific musical effects can be produced. Figure 3 shows that a wide vibrato can be readily generated on the reindeer phalanx whistle. Whether such a technique was used by Palaeolithic players is of course a matter for conjecture. Figure 2: Calculated input admittance curve for the re- production reindeer phalanx whistle [1] 2.2 The Isturitz flute A Palaeolithic bone flute discovered at Isturitz, in the The study of these earliest instruments illustrates a tech- Pyrenees, has also been studied acoustically [2]. The nique which has been widely applied to the detailed in- original instrument, which has four finger holes, was vestigation of historic instruments: the fabrication of an judged to be too fragile for playing tests, so the inves- accurate copy (Figure 1, left). The hypothesis that the tigation used replicas and numerical modelling of the cavity of the instrument could be treated as a Helmholtz resonance properties of the instrument. Input admit- resonator was considered and discounted, since the calcu- tance curves were calculated for different fingerings cor- lated Helmholtz resonance frequency of the reproduction responding to the successive opening of the side holes. was 3.4 kHz, and the half wavelength at this frequency From these, the probable playing frequencies of the flute (around 5 cm) is comparable to the long dimension of the could be deduced. elongated cavity. Instead the instrument was modelled as a tube closed at the lower end, and the input admittance The flute, in its present form, is considerably shorter than at the open hole was calculated. The resulting input ad- the bone from which it appears to have been constructed. mittance curve is shown in Figure 2. Is it possible that it was originally longer, and part of it 370 Forum Acusticum 2005 Budapest Campbell has been lost? The acoustical study, while not capable of giving a definitive answer to this question, certainly pro- vided some important guidance. It is possible on this type of flute to overblow from a first register (using the first air column modes) to a second register (using the sec- ond air column modes). For a model flute with the exist- ing dimensions, it was shown that the highest obtainable first register note (with all holes open) had practically the same frequency as the note obtained in the second reg- ister with all holes closed. This continuity of registers, which is also found on modern flutes, has obvious mu- sical advantages. Similar admittance calculations for a model instrument with additional length showed that this advantage was lost, suggesting that the existing length may well have been a deliberate choice. 2.3 Neolithic Chinese flutes Another important collection of early bone flutes, dat- ing from around 7000 BC, was found in 1999 at Jiahu in Henan Province, China. The collection included instru- ments with 5, 6, 7 and 8 holes. Playing tests were carried Figure 4: A reproduction carnyx sounded by an artificial out on the best preserved instrument, with seven holes, mouth and playing frequencies were recorded [3]. Attempts to extend the tests to other seven hole specimens were dis- Museum of Scotland, which in 1994 commissioned the continued when cracking sounds were heard. reconstruction of a complete carnyx. Since then a fur- This discovery stimulated a team including Patricio de la ther reconstruction has been made for the musician John Cuadra and Chris Chafe at CCRMA, Standford Univer- Kenny, who has played it extensively in concerts and on sity, to develop a digital waveguide model which would recordings [9]. be capable of replicating the sound of the flutes now A number of acoustical studies were carried out on the judged to be too fragile to play, using as input data the replicas in the Musical Acoustics Laboratory of the Uni- measured physical dimensions of the instruments.