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|Year : 2008 | Volume
| Issue : 41 | Page : 99--104
High sound pressure levels in Bavarian discotheques remain after introduction of voluntary agreements
Dorothee Twardella1, Andrea Wellhoefer2, Jutta Brix3, Hermann Fromme1,
1 Department of Environmental Health, Bavarian Health and Food Safety Authority, Veterinaerstr. 2, 85764 Oberschleissheim, Germany
2 Department Air, Noise, Plant Safety, Bavarian Environment Agency, Buergermeister-Ulrichstr. 160, 86179 Augsburg, Germany
3 Bavarian State Ministry of the Environment, Public Health and Consumer Protection, Rosenkavalierplatz 2, 81925 Muenchen, Germany
Bavarian Health and Food Safety Authority, Department of Environmental Health, Veterinaerstr. 2, 85764, Oberschleissheim
While no legal rules or regulations exist in Germany, voluntary measures were introduced to achieve a reduction of sound pressure levels in discotheques to levels below 100 dB(A). To evaluate the current levels in Bavarian discotheques and to find out whether these voluntary measures ensured compliance with the recommended limits, sound pressure levels were measured in 20 Bavarian discotheques between 11 p.m. and 2 a.m. With respect to the equivalent continuous A-weighted sound pressure level for each 30-minute period (L Aeq,30min ), only 4/20 discotheques remained below the limit of 100 dB(A) in all time periods. Ten discotheques had sound pressure levels below 100 dB(A) for the total measurement period (L Aeq,180min ). None of the evaluated factors (weekday, size, estimated age of attendees, the use of voluntary measures such as participation of disc jockeys in a tutorial, or the availability of a sound level meter for the DJs) was significantly associated with the maximal L Aeq, 30min . Thus, the introduction of voluntary measures was not sufficient to ensure compliance with the recommended limits of sound pressure levels.
|How to cite this article:|
Twardella D, Wellhoefer A, Brix J, Fromme H. High sound pressure levels in Bavarian discotheques remain after introduction of voluntary agreements.Noise Health 2008;10:99-104
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Twardella D, Wellhoefer A, Brix J, Fromme H. High sound pressure levels in Bavarian discotheques remain after introduction of voluntary agreements. Noise Health [serial online] 2008 [cited 2023 Jun 6 ];10:99-104
Available from: https://www.noiseandhealth.org/text.asp?2008/10/41/99/44348
High sound pressure levels are known to cause hearing impairment. According to occupational health studies, a noise-induced permanent threshold shift (NIPTS) can occur after long-term exposure to sound pressure levels ≥ 85 dB(A).  The risk for hearing depends on the sound level and exposure time. According to the equal energy principle, an exposure to 85 dB(A) for 40 hours per week has the same effect on hearing as the exposure to 95 dB(A) for four hours per week, or an exposure to 101 dB(A) for one hour per week. 
Typical sound pressure levels of music at public events have been shown to be as high as 100 dB(A) or more. , Thus, it must be assumed that frequent visits to concerts or discotheques can cause NIPTS in the long run. Hence, in 1999, the German Medical Association called for a restriction of sound pressure levels in discotheques to 95 dB(A).  The DIN 15905-5 was revised to establish new standards for the measurement and assessment of sound levels at discotheques and other music events, and thus, to reduce the risk for hearing among the audience.  The Association of German Discotheques and Dance Clubs (Bundesverband Deutscher Discotheken und Tanzbetriebe e.V.) developed the project "DJ license" in cooperation with the Association of Disc Jockeys (Berufsverband Disc-Jockey e.V.). This project was initiated by state health ministries and supported by health insurance companies in several German states.
As part of the project, "DJ license," a three-hour tutorial was offered to DJs in which the physics of sound, the physiology of the ear, the impact of loud music on hearing, and technical possibilities of action were taught. The aim of this tutorial was to educate the DJs and to foster a responsible handling of high sound levels. In particular, DJs were asked to keep sound pressure levels below 100 dB(A) and use sound level meters, which enable the DJs to recognize the actual sound levels on the dance floor and to react to overly loud music. While these voluntary measures were offered, no legal rule or regulation exists yet to restrict sound pressure levels in German discotheques.
The aim of the current research project was to i) investigate the sound pressure levels in Bavarian discotheques after the introduction of the described voluntary measures, ii) evaluate whether the recommended limit of 100 dB(A) is adhered to, and iii) determine the factors associated with reduced sound pressure levels.
Materials and Methods
Selection of the measuring sites
Measurements were taken in 20 discotheques in Bavaria selected on the basis that the participating discotheque did not have a sound pressure level limiter integrated into their public address system. The discotheques were a convenience sample of discotheques whose owners were known to be interested in measurements, and of additional discotheques located in the vicinity of the measurement institutes. Participation was on a voluntary basis, and the agreement of the owner was obtained in each case. As the measuring equipment was usually set up in the presence of the DJs, background information was obtained from DJs at the beginning of the evening, making the DJs aware of the measurements. The measurements were carried out between October 2005 and December 2006. In the majority of discotheques (n = 13) sound levels were measured in November and December 2006. Ten of the 20 participating discotheques were located in Munich and the surrounding area, the remaining in other Bavarian cities such as Augsburg, W�rzburg, and N�rnberg.
Data collection and measurements
Sound pressure levels were recorded for each discotheque, preferably on one night with high attendance, between 11 p.m. and 2 a.m. in the morning. Measurements were made by two different institutes using identical methods; each institute conducted measurements in ten discotheques: A microphone was placed above of the dance floor (preferably above the center of the dance floor), and was connected to the measurement equipment. The height of the microphone varied according to constructional conditions. Both institutes employed class 1 measurement equipment according to DIN EN 61672-1:  a sound level meter Br�el and Kjaer 2231 (calibrated) in combination with the evaluation program Symphonie db32, or a sound level meter Norsonic Type 116 (calibrated), respectively. These sound level meters conduct measurements every 20 ms, including a frequency spectrum. The single measurements were summarized for each 30-minute period between 11 p.m. and 2 a.m. for the following parameters:
L Aeq,30 Min : equivalent continuous A-weighted sound pressure level
L Cpeak : C-weighted peak sound pressure level (peak level)
A 30-minute time interval was chosen as this is the standard given in the January 2006 draft of the DIN 15905-5 which documents regulations for the assessment of sound pressure levels in discotheques.  Furthermore, the equivalent continuous A-weighted sound pressure level was determined for the total measurement period (L Aeq,180Min ). According to the DIN 15905-5 draft, the equivalent continuous A-weighted sound pressure level should not exceed 99 dB(A) and the C-weighted peak level should not exceed 135 dB.
In parallel to the stationary measurement, sound pressure levels were also measured with personal dosimeters (dose badge CK:110A/10, Cirrus Research, Dresden) in some discotheques. The personal dosimeters were worn by two subjects, who were asked to behave as usual in a discotheque. In addition, the measurement conditions, e.g ., the size of the discotheque, music style, availability of a sound level meter for the DJ etc., were documented in a form.
Firstly, the measurement conditions in the discotheques were described, such as the day of the week, the size of the discotheque and the dance floor, attendance, estimated age of the visitors, music style, attendance of the DJ at the tutorial, availability of a sound level meter for the DJ, and the height of the microphone above the dance floor.
Next, the progression of the sound pressure level during the measurement period was described, using L Aeq,30Min and the L Cpeak . The number of discotheques which reached an equivalent continuous sound pressure level of 100 dB(A) during at least one period of the 30 minute interval, or which exceeded a C-weighted peak level of 135 dB, was determined. The maximal L Aeq,30Min during the measurement period was used to describe the sound level in each discotheque and the conditions in the discotheque were assessed with respect to this value. Analysis of variance was employed to determine the statistical significance of the differences in mean maximal sound levels between different categories of discotheques.
Furthermore, sound levels determined by the personal dosimeter were compared to the sound levels determined by the stationary measurements.
All analyses were implemented in SAS, release 9.1.3.
Measurements were carried out mostly on weekends [Table 1]. Both small and large discotheques that covered different music styles and attracted different age groups, were included. DJs were reported to have participated in the tutorial in only five of the discotheques, and a sound level meter was available for the DJ in only four discotheques.
In the first 30-minute period (11-11.30 p.m.), the median equivalent continuous A-weighted sound pressure level was 97 dB(A) [Figure 1]. This level increased during the night and reached 101 dB(A) in the last 30-minute period. Similarly, the median C-weighted peak sound pressure started at a relatively low (127 dB(C)) level and stopped at 131 dB(C) [Figure 2]. The highest value of the L Cpeak was 136.7 dB(C).
Assessment of the single equivalent continuous A-weighted sound pressure level for each 30-minute period showed that the sound pressure level remained below the limit of 100 dB(A) in all time periods in only four of the 20 discotheques. The L Aeq,180Min was 92.5-105.3 dB(A) with a median value of 100.0 dB(A). The equivalent continuous A-weighted sound pressure level for 180 minutes (L Aeq,180Min ) was below the limit of 100 dB(A) in ten discotheques. The peak level exceeded the recommended limit of 135 dB(C) in six discotheques. The maximal L Aeq,30Min was 94.8-106.8 dB(A) with a median value of 101.4 dB(A). In only one discotheque did the sound pressure level not reach 95 dB(A) during any of the 30-minute periods. In this discotheque, Rock 'n' Roll, Oldies, Punk, Rock, Ska, and Alternative music was being played and the audience was small.
None of the evaluated factors was significantly associated with the maximal L Aeq,30Min [Table 2]. Sound pressure levels appeared to be higher on Saturday nights and in discotheques with a higher number of visitors, but these associations did not reach statistical significance.
Sound pressure levels were not found to be low in discotheques in which the DJ was reported to have participated in the tutorial, or in those in which a sound level meter was available. In fact, the equivalent continuous A-weighted sound pressure level reached at least 100 dB(A) in four of the five discotheques in which a DJ was reported to have participated in the tutorial, and in all the discotheques with a sound level meter.
In general, the sound pressure level measured with personal dosimetry was similar to but slightly lower than those obtained by stationary measurements [Table 3].
Our research project shows that despite voluntary agreements and training programs for DJs, sound pressure levels in Bavarian discotheques are still high and exceed the recommended limits. Even DJ participation in a tutorial or the availability of a sound level meter does not guarantee adherence to recommended limits.
Our findings that sound pressure levels often exceed 100 dB(A) is in agreement with other studies from Germany as well as other parts of the world [Table 4]. Even higher sound pressure levels were observed (geometric mean of 103.4 dB(A)) in a review of older studies.  In an investigation of discotheques in Berlin in 1984, the proportion of discotheques with sound pressure levels of at least 100 dB(A) was higher (2/3) than in our investigation (50%), and the maximum level was 110 dB(A).  In more recent investigations, sound pressure levels were lower (maximum sound pressure level 100 and 106 dB(A), respectively) and more similar to our results. , Recent measurements from England are consistent with our findings, although in our study, unlike the British study, the owners were informed about the measurements. 
No results have been published yet regarding potential factors influencing sound pressure levels. It has only been reported that sound pressure levels at live concerts are usually even higher that those in discotheques.  However, we were not able to identify any factor significantly associated with a high sound pressure level, which might be due to the low sample size and the corresponding low statistical power of our study.
None of the voluntary measures introduced to reduce sound pressure levels in discotheques showed any effect. This finding is disappointing as it was hoped that these measures would have a positive influence on the DJs and their handling of loud music. However, as our study is not designed as an intervention trial, data about sound pressure levels were not collected before the introduction of these measures, and thus, no information is available about the potential modification of sound pressure levels. Furthermore, while participation in measures has not been randomized, it can not be excluded that DJs from large and loud discotheques tend to participate in the tutorial. Likewise it is possible that sound level meters have been made available particularly in those discotheques which have received complaints because of very loud music, and that those discotheques still remain louder than other discotheques. While conclusions can not be drawn about modifications in sound pressure levels due to the introduced measures, the data still show that sound pressure levels are high and exceed the recommended limits in discotheques which have acquired a sound level meter, and in which the DJ has participated in the tutorial. Therefore, the current investigation does not support the hypothesis that voluntary measures are sufficient to guarantee compliance with recommended limits for sound pressure levels.
While we aimed for a maximum standardization of sound pressure level measurement, some differences in methods can not be excluded. For example, the microphone was supposed to be fixed over the center of the dance floor. However, this was not possible in some cases due to the absence of possibilities for fixation of the microphone in that spot, and an alternative location had to be selected. This might have caused an over- or underestimation of the sound levels that the guests were exposed to. However, in all cases the microphone was basically installed in the loudest area of the discotheque.
In two discotheques, a sound pressure level limiter was integrated into the public address system. The first was a small discotheque playing pop music in which the maximal L Aeq,30Min reached 97.5 dB(A), whereas the second was a middle-size discotheque playing house music in which a maximal L Aeq,30Min of 102.1 dB(A) was obtained. Thus, the suggested limit of 99 dB(A) can be exceeded even in the presence of a limiter.
A generalization of our findings is not permissible for all discotheques in Bavaria as our design did not ensure a representative sample, but rather a convenience sample of already known discotheques or discotheques close to the measuring institutes. About half of the discotheques contacted declined to participate. If those known to be "loud" refused participation, our results would be an underestimation of typical sound pressure levels in discotheques. In addition, sound pressure levels may vary depending on the day of the week, the style of music, the DJ etc. The measurement of the sound level on only one night may thus not be a good indicator for the typical sound levels in one discotheque. To overcome these pitfalls, several strategies were implemented: (1) discotheques were selected from different cities in Bavaria and were of different sizes and types, (2) after consulting the club owner, a night of high attendance was selected for the measurement. Thus, we attempted to cover a wide spectrum of discotheques and relevant sound pressure levels.
To obtain data on the possible exposure of the audience, personal dosimetry was conducted in addition to stationary measurements, and slightly lower sound pressure levels were observed. The difference might be due to the fact that the stationary measurement is supposed to correspond to the loudest area accessible to the public, whereas subjects do not stay in this area for the whole night. While no data were collected on effects on hearing within this investigation, it can be assumed that the observed high sound pressure levels can cause hearing impairment among attendees who visit discotheques on a regular basis over many years.
The results of our investigation show that sound pressure levels in discotheques are high even after the introduction of voluntary measures, and recommended limits are not met. As the observed sound pressure levels are likely to cause hearing impairment among attendees in the long run, other measures appear to be necessary to protect the hearing of young adults from a noise-induced permanent threshold shift caused by discotheque visits.
We wish to thank the licensees of the discotheques for their good cooperation and kindness. This work was funded by the Bavarian State Ministry of the Environment, Public Health and Consumer Protection. This work has been presented at the Congress "Medizin und Gesellschaft" in Augsburg, September 17.-21., 2007.
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