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| Year : 2011
| Volume
: 13 | Issue : 50 | Page
: 59-63 |
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| Noise exposure of musicians of a ballet orchestra |
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Cheng Liang Qian1, Alberto Behar2, Willy Wong1
1 Edward Rogers Sr. Department of Electrical and Computer Engineering; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada
2 Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada
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| Date of Web Publication | 15-Dec-2010 |
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With over 70 dancers and its own orchestra, The National Ballet of Canada ranks amongst the world's top dance companies. It performs three seasons annually: fall, winter and summer, plus many shows of Tchaikovsky's Nutcracker. The 70-strong orchestra plays an average of 360 hours/year including rehearsals and performances. Rehearsals are held at two locations: one in a ballet rehearsal room with little or no absorption, and the other in an acoustically treated location. Performances are held in the Four Seasons Centre for the Performing Arts in Toronto. The present survey was done at the request of the National Ballet, since the musicians complained of excessive sound levels and were concerned about possible hearing losses. The survey was performed using five dosimeters Quest Mod 300 during 10 performances of the ballet Romeo and Juliet by Sergei Prokofiev, deemed as the noisiest in the whole repertoire. Results of the survey indicate that the noise exposure levels from only the orchestra's activities do not present risk of hearing loss. Exposure due to other musical activities was, however, not included. Keywords: Noise exposure, dosimetry, field measurement, musician, orchestra
How to cite this article:
Qian CL, Behar A, Wong W. Noise exposure of musicians of a ballet orchestra. Noise Health 2011;13:59-63 |
| Introduction | |  |
Musicians at the National Ballet of Canada's orchestra were concerned about the high noise levels they were exposed to during performances and rehearsals. To assess the actual noise exposure and the risk of hearing loss, the management requested a study to be performed by the Sensory Communications Group at the University of Toronto. The Group has already performed two similar studies in the past on musicians from the Canadian Opera Company [1],[2] and through these studies has an established measurement methodology.
The present study consisted in the measurement and assessment of noise exposure of musicians during 10 performances of Sergei Prokofiev's "Romeo and Juliet" - a particularly loud 3-hour ballet. This composition requires a relatively large, 70 player orchestra. Furthermore, the noise levels in the orchestra pit may be higher compared to an open symphonic stage, where symphonic orchestra performances and rehearsals typically take place. The higher levels are due to the enclosed space that increases the reverberant energy of the sound. The measurements are best representative of a pit musician's noise exposures during actual live performances.
Noise-induced hearing loss is the result of long exposures to high sound levels. Measurements of those levels are performed using noise dosimeters that integrate the noise levels for the entire duration of the event. The result is shown as Leq,t. 1Leq,t is the equivalent noise level during the time t, obtained using a 3 dB exchange rate
When a measurement is performed for a duration different than 8 hours, the result has to be converted to the equivalent 8-hour exposure Leq,8 using the formula
where t is the actual measurement duration (hours).
Musicians at the National Ballet Company perform for 360 hours/year, as opposed to the usual 2000 hours/year (8 hours/day) in the case of workers in other industry. For 2000 hours, Equation (1) becomes
Using t = 360 hours, Equation (2) becomes
| Measurements | | |
Measurements were performed during 10 performances of the ballet "Romeo and Juliet" by Prokofiev. All performances were held at the Four Seasons Centre for the Performing Arts. Inaugurated in 2006, this is the first theater in Canada built specifically for opera and ballet. Presently, it is considered as one of the finest halls in the world.
| Measuring Instruments | | |
Five Quest Q-300 dosimeters were used during each performance. They were set to measure Leq following the guidelines in CSA Standard Z107.56-94. [3] Instruments were set up and calibrated in our laboratory using the manufacturer's QuestSuite Application software.
| Dosimeter Locations | | |
The set-up consisted of dosimeters, each with a cabled microphone. Each dosimeter was clipped to the musician's belt, with the microphone attached to the collar or shoulder seam of the musician's shirt on the side chosen by the player. In the case of shoulder-borne instruments such as the violin, the microphone was attached to the right shoulder of the player.
Since only five dosimeters were used, it was intended that the number of tests per instrument be approximately proportional to the number of players of this instrument. In addition, certain musicians were measured in more than one performance. Nevertheless, an even spatial coverage of the orchestra pit was achieved.
[Table 1] shows the total number of players for each instrument and the number of separate measurements performed on players of this group.
| Measurement Procedures | | |
Approximately 15 minutes before the start of a performance, each designated musician was fitted with a dosimeter. The operator in charge of the test attached personally the microphone of the dosimeter to the collar of the musician (according to the instrument played, it was attached either to the left or the right side of the musician's body). Then, the microphone cable was fixed to the back of the musician. This was done to avoid interfering with the musician's performance, or creating a potential safety hazard.
The operator further kept a record of the following: the name of each of the five musicians tested on that particular day, their instruments, their locations on the floor plan and the start and end time of the testing.
At the end of the performance, the operator followed the procedure of stopping the data collection, disconnecting the microphone, removing the dosimeter from the musician and recording the measured Leq from the dosimeter.
| Measurement Results | | |
[Table 2] summarizes the results of the noise exposure measurements performed on the different musicians. All results are Leq,3 (dBA), i.e., the actual reading on each of the dosimeters after each performance.
It can be seen that the numbers of measurements for the different musician groups vary between 2 and 6. As mentioned earlier, some musicians wore the dosimeters for more than one session. This was done to investigate the variation in Leq,3 across different performances. These particular results are underlined in the table.
The mean Leq,3 shown in the last column of the table corresponds to the energetic average of the measured values given by Equation (4).
[Figure 1] below represents the floor plan and the seating distribution of the players within the pit. A few of the musicians are located under an acoustically transparent overhang that is used as a safety net to stop objects (and even dancers) from falling into the pit. The end of the overhang is indicated by the curved line on the figure.
| Discussion | | |
Variations of noise exposures in the orchestra pit
The variations of the noise exposure of musicians in the orchestra pit can be attributed to a combination of factors. These include the sound power of the instrument the musician is playing, of the instruments in the vicinity, the time variation aspects of the music, and of sound reflections from the limiting surfaces.
A comparison of the sound exposure from different instruments is presented in [Figure 2]. Instruments are grouped by their location within the pit and ordered from lowest to highest mean sound exposure. The woodwinds are separated into flutes and the remaining woodwinds, as there was a significant (P < 0.001) difference in measured sound exposure levels between these subgroups. Since the string sections were also separated spatially [Figure 1], sections were divided into three subgroups: a) violins, b) viola and cello, and c) double bass. There were significant (P < 0.01) noise exposure level differences between double bass and all other string instruments. | Figure 2: Leq min, mean [see Equation (3)] and max of various instrument sections as grouped by location. Sections are ordered from lowest to highest mean sound exposures
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Furthermore, there was a surprising statistical difference (P < 0.05) between the sound level of the 1 st violins and 2 nd violin section even though these two sections are composed of the same instruments, located adjacent to each other. This difference may be best explained by the fact that the 1 st violins were seated next to the pit wall, and were thus subjected to additional exposure from reflections from the nearby wall. This highlights the potential difference in sound exposure between pit orchestra and stage orchestra musicians.
Variability within same instrument group and same musicians
To estimate the variability within the same instrument and musician across multiple performances, a few musicians were measured more than once. In general, these repeated measurements yielded very similar Leq results (see underlined entries in [Table 2]). With the exception of one viola player and percussionist, the measurements were within 2 dB of one another, a difference well within measurement error. The data support the idea that professional orchestras are quite consistent (in terms of sound level at least) across several performances of the same work. This can also be inferred from the relative consistency (also within 2 dB range) of measurements within each instrument section when measured across performances. For future assessments, this suggests that a few measurements per instrument section can adequately characterize sound exposure over several performances of the same piece.
The larger variability of sound exposure measured on the percussionist and viola player are easily explained. Percussionists, unlike other orchestra musicians, move quite dynamically between several different locations (playing several percussion instruments) during the performance, adding extra variability.
One viola player represented an interesting case that illustrates the impact of the location of the dosimeter microphone. He was measured twice, first with the dosimeter microphone on the shoulder opposite their instrument. For the next measurement, he decided to wear the microphone on a headband pointing down at their viola. This yielded measurements of 86.5 and 89.1 dBA, respectively, with a difference representing roughly a doubling of the sound energy. This suggests that future studies should consider making creative efforts to measure on the side of the body exposed to the higher levels, to obtain more conservative estimate of the sound exposure.
Are these musicians at risk of hearing loss?
The most important question addressed in the study is whether musicians are at increased risk of hearing loss after years of performance in orchestra pits. We used the ISO 1999:1990 threshold shift algorithm [4] to predict the noise-induced permanent threshold shift (NIPTS) expected in an individual musician as a function of the exposure level (in Leq,8 ) and their percentile susceptibility to hearing damage.
Though performances in the orchestra pit only occupy a portion of a musician's time, they likely constitute the highest exposure levels due to the sheer number of instruments being played nearby. To arrive at a reasonable Leq,8 from the Leq,3 measured during performance, two additional assumptions must be made. Firstly, it is assumed that this piece of music is representative of the typical sound levels of performances. Prokofiev's "Romeo and Juliet" is actually one of the loudest performances of ballet music, and so assessing general risk based on this piece may lead to erroneous conclusions. The second assumption is that other activities such as practice, other performances and/or teaching do not contribute significantly to the total level of exposure, relative to the exposure from performances. This may not be a fully valid assumption and cannot be easily verified without continuous dosimeter measurement of a musician throughout their daily activities. Musicians themselves need to be conscious of any other activities that might significantly increase their exposure, such as teaching group music classes.
To compute Leq,8, the measured Leq needs to be adjusted [using Equation (2)] by −7.4 dB corresponding to 300 hours of performance compared to the 2000 hours of work assumed by Leq,8. After this adjustment, the Leq,8 of several instrument groups fall immediately to below 80 dBA, which is widely considered as presenting minimal risk. Two instrument groups, brass and flutes/piccolos, have higher exposures with mean Leq,8 of 85.4 and 85.6 dBA, respectively. For these players, the projected hearing loss (after a 40-year career in performance) due to exposure alone is calculated using the ISO1999:1990 algorithm [4] and is presented in [Figure 3]. It is easy to see that under the assumptions of this calculation, even the musicians in this group who have the highest vulnerability to noise are only expected to experience mild shifts (<10 dB) in hearing threshold. | Figure 3: Noise-Induced Permanent Threshold Shift (NIPTS) projections of musicians (playing brasses and flutes) measured at 93 dBA ( Leq,8 = 85 dBA), after performing for 40 years. Each curve represents predictions for a different percentile resistance to hearing damage. For example, 50 percentile is the median and 90 percentile means top 10% resistance. All threshold shifts are mild and <10 dB even for the most susceptible part population
Click here to view |
However, since hearing is typically more important to musicians than other individuals, musicians may still wish to reduce the risk of hearing loss. To this end, a reduction of 5 dB in sound exposure to approximately the same level as the remainder of the orchestra will minimize the risk for brass and flute players such that the predicted NIPTS is <3 dB. Some recommendations on providing this amount of noise exposure reduction are presented in Appendix-A.
| Conclusion | | |
The present work was an assessment of pit orchestra musicians' risk of noise-induced hearing loss. We have highlighted several considerations for proper and efficient assessment of orchestra-related sound exposure, including the fact that the accuracy of the noise exposure measurement is within 2 dB.The measurements done over one particularly loud ballet piece (Prokofiev's "Romeo and Juliet") indicate that musicians of the National Ballet of Canada Orchestra are, in general, not overexposed due to performances alone. The conservative assumption in this study was that the measured noise exposure applies to all orchestral activities of the musicians, including rehearsals and playing other pieces, while it actually represents the noisiest activity they are likely to partake in.
| References | | |
| 1. | Lee J, Behar A, Kunov H, Wong W. Musicians' noise exposure in orchestra pit. Applied Acoustics 2005;66:919-31. 
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| 2. | MacDonald E, Behar A, Wong W, Kunov H. Noise Exposure of Orchestra Musicians. Canadian Acoustics 2008;36:11-6.
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| 3. | CSA Standard Z107.56-06. Procedures for the measurement of occupational noise exposure. Canadian Standards Association; 2006.
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| 4. | ISO Standard 1999:1990. Acoustics - Determination of occupational noise exposure and estimation of noise-induced hearing impairment. International Organization for Standardization; 1999.
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Correspondence Address:
Cheng Liang Qian
1317-438 King St. West. Toronto, ON
Canada
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/1463-1741.74002
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2] |
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