The following equipment (Table 7-1) was utilised during the music survey. The data collected and noise descriptors used are given for each category of measurement.
Table 7-1 Table of equipment used and descriptors of data obtained during music survey
Instrument Purpose Noise descriptors used
Cirrus doseBadges Personal sound exposure
of musicians Dose% and Pa
2h
LAeq dB
LPeak dB
LAmax dB
Quest M28 sound level meters (where musician has not consented to have the doseBadge)
Mainly used for fixed measurements in various parts of the orchestra, but also used sometimes for personal sound exposure of musicians LAeq dB LPeak dB LAmax dB Sometimes also: Dose% and Pa2h Pulsar 60 personal sound
exposure meter
Personal sound exposure of musicians Dose% and Pa2h LAeq dB LPeak dB LAmax dB Cirrus 831 integrating sound level meter
Fixed measurements in various positions in the orchestra
LAeq dB
LPeak dB
LAmax dB
Brüel and Kjær Type 2236 Integrating Sound Level Meter
Fixed measurements in various positions in the orchestra
LAeq dB
LPeak dB
LAmax dB
Quest 500 integrating sound level meter
Personal sound exposure of musicians Dose% and Pa2h LAeq dB LPeak dB LAmax dB 7-8
LAeqdB = Time-average levels (A-frequency weighted).
Dose % and Pa2h = the personal sound exposure expressed as either Dose % or in pascal squared hours: 1.0 pascal squared hour = 100% dose, which is equivalent to LAeq 8hours = 85dB.
Lpeak dB = Peak level (unweighted or C-frequency weighted).
LAmax dB = Maximum sound pressure level (A-frequency weighted).
7.10.1 Fixed sound level measurements
Typical sound pressure levels in the orchestra were recorded by the fixed sound level meters. The Quest M28 sound level meters were mainly used for the fixed measurements in various positions in the orchestra, but were sometimes used as dosimeters. For additional fixed monitoring, the CR 831 and Quest 500 meters were used. While it would have been ideal to place the microphones of the sound level meters close to the ears of the musicians, the possibility of unintentional damage interfering with the musicians’ free movement and routine activity precluded this option. Microphones for all the sound level meters were connected to the meter by extension cable, and the microphone was attached to the stand in front of the musicians as close as possible with the sound level meter suspended under the stand with a small black string. Where possible, the meters were placed away from walls or other reflective surfaces. While no standard or codes of practice exist for the measurement of music, the relevant measurement requirements of the New Zealand standard for measurement of environmental sound were applied where it was possible. The practice of placing sound level meters on a tripod at a height of 1. 2- 1.5 meters above the ground for measurement was not possible.
The following noise descriptors were recorded:
A-frequency weighted time-average levels (LAeq ) Maximum sound pressure levels (LAMax)
Peak levels (Lpeak)
The period of time sampled
A Log of events was kept to ascertain, as much as possible, the events occurring.
A time history was produced for each set of fixed sound level measurements. An example is shown in Figure 7-2.
As mentioned before, all the meters were calibrated with an acoustic calibrator before each measurement and checked at the end of the measurement session in accordance with manufacturer’s instructions and for the standardand code of practice promulgated in New Zealand.
Figure 7-2 Typical time history illustrations from fixed sound level measurements
7.10.2 Personal sound exposure of musicians
The difficulty of monitoring the personal sound exposure of musicians while they are playing music and having the microphone close to the ears was overcome with the acquisition of the new lightweight noise doseBadge.
Figure 7-3 DoseBadge with the reader unit
These instruments were developed to monitor workers in confined spaces where traditional personal sound exposure meters would not be possible to place, and they are small and lightweight enough to fit comfortably on children and adults. The doseBadges were certified as intrinsically safe and do not emit any kind of radiation such as radio waves while being worn. These units were inserted into the reader unit, and the memory was cleared, calibrated and activated (as shown in figure 7.3). The doseBadge was pinned to clothing, and for some musicians, the doseBadge had to be placed on the shoulder away from the instrument to prevent it interfering with the playing.
Prior to the musician leaving the session, the Badges were turned off, removed and data transferred into the reader unit as shown in Figure 7-3. It would have been desirable to have documented the sound exposure for both rehearsal and performance, but the management of the orchestra was reluctant to grant permission for such measurement to be made during the orchestra performance. Later, all the
data from the reader unit was downloaded in duplicate and processed with the accompanying doseBadge software and the Cirrus Acoustic Editor program.
The data collected from the doseBadges and personal sound exposure measurements was as follows:
A-frequency weighted time-average levels (LAeq ) Dose %
Pascal squared hours (Pa2h)
Maximum sound pressure levels (LAMax) Peak levels (Lpeak)
Time sampled.
A time history was produced for each set of personal sound level measurements. An example is given with explanations in Figure 7-4. A-frequency weighted time average level lines have been added for the full sampling period (LAeq = 85dB) and for the one-hour period between the cursors (LAeq 1h = 82dB). The doseBadge software has a capacity to produce dosimetry reports where the data from each Badge use in the same sampling session can be compiled into a single report for ease of data management.
Dosimetry reports were generated for each set of measurements. An example is given in Appendix N. The doseBadges were designed for adult use in confined spaces and for compliance with the international occupational noise criteria of:
A-frequency weighted time-average level of no more than 85dB for eight hours or equivalent (100% dose or 1.0 Pa2h), 75dB -0.1, and 65dB -0.01. A peak level of no more than 140dB.
The data collected was compared to the above criteria, which are also a legal requirement of Regulation 11 of the New Zealand Health and Safety in Employment Regulations 1995. Even though the above criteria do not apply to children in
learning environments, the data collected from the doseBadges was compared to these criteria, as no other standards were available. However, it is reasonable to assume that exposure of young children to noise levels approaching the above occupational criteria is excessive.
The doseBadge being a very small unit has a memory limitations. It has a high cut- off point where noise exposure data of less than 75dB is discarded. This is not entirely suitable for children, which gives a conservative estimate of the children’s exposure. Information on levels of noise, which will cause damage to young children, is problematic due to lack of information on this topic. The best guidance on this is given by the World Health Organization (1999), where they estimate that time-average levels over an 8-hour day of 75dB are unlikely to cause significant harm across the population. A lower cut-off point at 65dB would have been useful, but the meter did not have this capability.
Note: the time scale is GMT (the default setting on the meter)
Figure 7-4 typical time-history from a doseBadge