- Email: [email protected]
Incidence of spontaneous hearing threshold shifts during modern concert performances
Otolaryngology–Head and Neck Surgery (2006) 134, 667-673
ORIGINAL RESEARCH
Incidence of spontaneous hearing threshold shifts during modern concert performances David A. Opperman, MD, William Reifman, NP, PA, Robert Schlauch, PhD, and Samuel Levine, MD, Minneapolis, Minnesota
odern-day music performances often consist of long periods of high volume sound and short periods of rest between music sets. Although it is known that intense levels of noise exposure can cause irreversible damage to the hearing mechanism, regular exposure to less intense, but still noisy environments, may also involve the insidious destruction of inner-ear components that unavoidably leads to an elevation in hearing thresholds. It has been clearly understood that at low levels for long
periods of time, hearing loss will occur. Similarly, there can be a single intense loud sound that will cause a permanent hearing loss.1 These issues have been studied well and are agreed on in the literature. The development of a hearing loss caused by habitual exposure to this level of noise (noise-induced hearing loss [NIHL]) typically involves decreased hearing acuity, occurring immediately after noise exposure and lasting for a variable period of time thereafter. This is referred to as a temporary threshold shift. Although there is no clear definition of how long a temporary shift can last if this threshold shift does not recover, irreversible cochlear damage has likely occurred, resulting in a permanent threshold shift. Such permanent threshold shifts are often accompanied by other common symptoms of hearing dysfunction including tinnitus, loudness recruitment, and frequency distortion, which have significant morbidity associated with them. NIHL commonly occurs after prolonged exposure to noise greater than 85 dBA. In the workplace, OSHA (Occupational Safety and Health Act, 1983) currently has in place strict rules that limit the amount of noise exposure in order to prevent NIHL.2 These guidelines were promulgated from extensive research showing that the continued exposure to sound levels greater than 85 dBA would result in permanent hearing loss.3 Although the basis of these regulations has been challenged, general acceptance is seen in the regulatory community.4 These rules state that an individual may be exposed to 90 dBA for a maximum of 8 hours, and, as intensity increases, duration of exposure is mandated to be less. Thus, for noise of 100 dBA, exposure must be limited to 2 hours or less, and for noise of 115 dBA, exposure must be limited to 25 minutes or less (Table 1). If
From the Department of Otolaryngology-Head and Neck Surgery, University of Minnesota, 420 Delaware Street, S.E., Minneapolis, MN 55455.
Reprint requests: David A. Opperman, MD, Department of Otolaryngology, University of Minnesota, 7563 Teal Road, Woodbury, MN 55125. E-mail address: [email protected].
OBJECTIVES: Concerts have long periods of intense sound with short break intervals. Hearing concerns are well known to performers; concertgoers largely ignore them. Preperformance and postperformance audiograms were compared to assess hearing threshold shifts with and without earplugs. METHODS: A prospective, randomized study in which 29 volunteers attended 3 concerts, encompassing 3 music genres. Audiograms, seating location, sound intensity, and earplug-use data were collected. Data were analyzed to determine frequency test-retest variability. RESULTS: Sound levels averaged 99.8 dBA, and the maximum was 125.6 dBA. Sixty-four percent (9/14) of participants without earplugs showed significant threshold shifts compared with 27% (4/15) of those using earplugs. No significant differences existed between music genres or seating location. CONCLUSIONS: This study showed a high incidence of threshold shifts in unprotected concertgoers. Sound levels exceeded all Occupational Safety and Health Act rules despite standardized sound systems. A significant reduction in threshold shifts was seen with the use of earplugs. EBM rating: A-1b © 2006 American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. All rights reserved.
M
0194-5998/$32.00 © 2006 American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. All rights reserved. doi:10.1016/j.otohns.2005.11.039
668
Otolaryngology–Head and Neck Surgery, Vol 134, No 4, April 2006
Table 1 OSHA Standards for noise exposure greater than 85 dBA SPL Duration per day, hours
Sound level dBA slow
8 6 4 3 2 1.5 1 .5 .15 or less
90 92 95 97 100 102 105 110 115
there is concern that these limits may be exceeded, employees must be provided with hearing protection devices. The work place rules required by OSHA, however, do not apply to the paying concert-going community. In part, because of improved technology in sound amplification, the absence of noise regulations governing concert goers, and the idea that many individuals find loud music quite pleasurable,5 the level of noise exposure at a concert is likely to be quite significant. Various studies have found sound levels at rock concerts often to be significantly higher than 85 dBA and thus pose risk to attendants hearing. Cabot et al6 determined that the sound level at various concert venues was on average 95.3 dBA, and Sataloff7 cites peak levels at 139 dBA. Furthermore, there are studies that suggest that sound intensity at such venues may vary from 90 dBA to as high as 122 dBA.6 Also, a performance usually entails several hours of high-volume sound with several interspersed rest interludes in which the noise level may or may not significantly decrease. If levels are maintained at values greater than 85 dBA, this may (and often does) lead to exposure times that exceed the levels published by OSHA and frequent concertgoers may experience some potentially irreversible hearing loss from this experience. Although certain genres of music, such as heavy metal, with its aggressive rhythms and amplified, distorted guitars, have a reputation for being excessively loud, it is unclear whether other more mainstream genres of music played at concerts may also pose the same risk to attendants’ hearing. These hearing concerns are well known to performers; they are largely understated and ignored by concertgoers. This may have the potential to result in widespread, detrimental, although preventable, hearing loss. It has been recommended that ear plugs be worn by those attending live music concerts,8 and in 1 study that evaluated threshold shifts in performers and listeners, Axelson and Lindgren9 showed a larger degree of hearing threshold shift in the audience as compared with the performers. Despite these results, however, most concertgoers opt not to use such devices. We undertook this study to examine sound intensity levels throughout a well-known concert venue and the ef-
fectiveness of earplugs during pop, heavy metal, and rockabilly music performances. Furthermore, observations were made regarding sound levels within a venue for the duration of the concerts. Are sound intensities maintained at high levels for a time exceeding the OSHA rules? And, finally, are commercially available foam ear plugs effective in pre-
Figure 1 Venue floor plan. Red dots represent participants’ locations during concerts.
Opperman et al
Incidence of spontaneous hearing threshold shifts . . .
669
Table 2 Levels (dBA) by location within the concert venue for each music genre. Values calculated from data recorded during the duration of each concert Concert (duration in minutes) Pop (360)
Heavy metal (210)
Rock-a-billy (195)
Location
Average
Minimum
Maximum
Front Sound board Left Right Back Front Sound board Left Right Back Front Left Right Back
98.47 100.92 101.92 98.17 95.12 97.96 98.58 99.41 102.66 96.57 106.84 102.71 101.29 95.94
59.1 81.2 56.7 63.7 71.0 60.5 61.3 63.5 54.1 58.8 80.7 84.5 83.8 76.8
117.1 119.4 125.1 125.6 108.6 112.6 120.4 112.7 124.2 113.7 118.3 114.9 115.4 106.1
venting spontaneous hearing threshold shifts in concert attendees?
MATERIALS AND METHODS An agreement was reached with a popular music venue to allow this experiment to take place. Performers and the venue location are withheld as a precondition for permission to conduct the study. Twenty-nine people consisting of 14 females and 15 males, with an age distribution from 17 to 59 years, volunteered from the local concert-going community to participate in an institutional review board–approved prospective, randomized study to determine the sound intensity throughout a venue and the effectiveness of earplugs at preventing hearing-threshold shifts during 3 concerts, encompassing pop, heavy metal, and rockabilly music genre. This experimental protocol was reviewed and conducted in accordance with the institutional review board at the University of Minnesota. Each of the participants agreed to have audiograms recorded immediately before entering the venue and again immediately after the concert. These audiograms were obtained in a mobile sound booth using a Benson CCA200 automated audiometer, integrated with a sound-level meter (Benson Medical Instruments, Minneapolis, MN), factory calibrated yearly and locally before each use. Also, each participant agreed to fill out a brief medical and noise exposure history to help determine eligibility for the study. To be allowed to participate, participants had no evidence of progressive hearing loss by history and had normal/near normal hearing thresholds at the time of their preconcert audiogram. Seating assignments were randomly assigned as was whether or not a person would be wearing ear plugs. Spe-
cific seating locations were standardized by arrangement with the venue to ensure consistency within the 3 chosen concert floor plans (Fig 1). Two participants were placed in the front-row center position, 2 were placed behind the railing on the stage-right and stage-left staircase positions, 2 were seated at the soundboard, and 2 were placed at the rear of the floor seating area. At each seating location, 1 participant wore ear plugs during the entire concert performance and during all rest periods, whereas the other wore only a recording microphone and dosimeter. Each venue position was monitored for sound pressure levels (SPLs) using a dBA scale once every minute (slow) over the entire concert by way of the computer-controlled dosimeters (705 NoiseBadge; Larson Davis, Provo, UT). The selected ear plugs for this study, Mack’s Hear Plugs (McKeon Products, Inc, Warren, MI), were selected because of their marketing toward concertgoers, ease of use, and their noise reduction rating (NRR) of 21. The NRR represents the decibel attenuation provided by an earplug
Figure 2 position.
Average levels (dBA) for each concert by genre and
670
Otolaryngology–Head and Neck Surgery, Vol 134, No 4, April 2006
Table 3 After show minus before show difference in hearing levels, averaged over location and concert. Table includes mean difference and standard deviation 500 No ear plugs Ear plugs p-value (unadjusted) p-value (adjusted)*
1k
2k
3k
4k
6k
8k
2.86 (3.08) 3.04 (5.30) 5.36 (7.96) 10.18 (9.12) 11.61 (10.22) 8.46 (14.38) 3.57 (7.89) ⫺0.17 (2.75) 0.83 (2.94) 1.5 (2.96) 2.67 (7.76) 3.33 (6.17) ⫺1.00 (6.25) 0.33 (5.89) 0.010 0.186 0.107 0.024 0.043 0.043 0.219 0.011 0.214 0.118 0.019 0.038 0.38 0.291
*Adjusted for seating location and concert.
under laboratory conditions. In actual settings, OSHA considers the effective attenuation to be one half the NRR. Before each concert, all individuals randomly selected to wear ear plugs were instructed on the use and insertion of the plugs as directed by the product manufacturer by the principal investigator. Before each concert, sound output was standardized at the soundboard for a maximum level output of 105 db(A) SPL and both primary and relay sound systems were used during all 3 performances. Each system calibration was performed by the same technician, using industry standard equipment for each concert to maintain a standard for data collection.
RESULTS Table 2 summarizes the SPL on a dBA-weighted scale for the 3 examined music genres. Average levels were calculated from 1-minute interval recordings across the entire duration of each concert performance. The minimum and maximum values represent the highest and lowest values during each concert and thus define the SPL range. Graphical illustration of the average levels (dBA) for each concert is shown in Figure 2. A hearing-shift value was calculated using the after show minus before show differences in hearing threshold levels by frequency, averaged over seating location and concert. These are shown in Table 3. The after minus before show differences in hearing were averaged over the right and left
ear for each frequency and univariate analysis showed no significant difference between seating locations and concert. An overall analysis that evaluates all the frequencies simultaneously (repeated measures analysis of variance) showed a significant effect for earplugs (F1 ⫽ 8.83, P ⫽ 0.006) with no significant interaction between earplugs and frequencies. Individual audiograms were evaluated for significant threshold shifts using 3 methods: OSHA standard threshold shift (STS) criterion, ASHA (1994) criterion, and a multinomial statistical model. The OSHA STS criteria requires a 10-dB or greater change for a pure-tone average based on thresholds obtained from 2,000, 3,000, and 4,000 Hz. The ASHA (1994) criteria look for a decrease of hearing sensitivity of 20 dB or greater at any one frequency, a decrease of 10 dB or more at any 2 adjacent frequencies, or the loss of response at 3 or more consecutive frequencies where responses were previously obtained. The multinomial model examined whether a particular audiometric configuration on retest was likely to occur by chance alone. Multinomial probabilities were calculated based on the SD of intertest differences (5 dB) and the number of thresholds being measured in ear tested ear. Table 4 summarizes the number of individual ears that showed a threshold shift by each specific criterion and by the use or lack of earplugs. Table 5 shows the number of participants who showed a threshold shift in either one or both ears by each method. At the completion of each concert, time history plots were created to help explain visually the sound levels obtained across the entire length of each performance. An example of this is represented in Figure 3.
Table 4 Number of individual ears that demonstrated a threshold shift by specific criteria and by the use, or lack of earplugs Left ear
Ear plug No ear plugs
Significant threshold shift No threshold shift Significant threshold shift No threshold shift
Right ear
OSHA STS
ASHA
Multinomial
OSHA STS
ASHS
Multinomial
3 12 8 6
4 11 8 6
4 11 8 6
1 14 6 8
1 14 7 7
1 14 7 7
Opperman et al
Incidence of spontaneous hearing threshold shifts . . .
Table 5 Number of participants who demonstrated a threshold shift in either one or both ears by each method criteria OSHA STS
ASHA
Multinomial
3 9
4 9
4 9
Plugs No plugs
DISCUSSION With the vast array of concerts that tour in a given year, it is not surprising that a large number of people have been or will be concertgoers. What is surprising is that the vast majority of people attending these performances are unaware of the potential impact that the noise levels to which they will be exposed could have on their hearing. This study attempted to look at a single venue during 3 concerts of different music types to understand the concert environment better. What seemed an obvious prestudy question, namely, is music played at very high volumes at most concerts, only scratched the surface of the information gained. The new questions that arose form the results of the study. The concerts observed during this study ranged in duration from 195 minutes to 360 minutes, and the average SPLs were maintained above the recommended OSHA standard of 85 dBA over the entire course of each performance. Thus, even if the levels did not exceed 90 dBA, which they universally did, an attendee should only be exposed to this level of noise for a total of 120 minutes without the use of ear plugs. During performances in large indoor concert halls or outdoor venues, bands may employ the use of amplification equipment totaling upward of 500,000 W.6 Subsequently, noise levels can be excessive, as shown in this study, and hearing protection should be worn by all in attendance. In this study, all concerts had soundboard output standardized to 105 dBA. This would seem to indicate that output should be the same regardless of the music genre, which was in fact observed. Therefore, the misconception that one genre of music is louder than another may mislead concertgoers into feeling that the use of hearing protection is unnecessary at some concerts, thereby exposing them to unnecessary risk of hearing loss. Furthermore, crowd noise can be substantial even in large venues as shown by official recordings at the Metrodome in Minneapolis, MN, during the 1987 World Series. During that game, decibel recordings peaked at 125 dB, a level beyond the threshold for pain and louder than a 727 jet taking off 300 yards away.10 Despite this, few people wear hearing protection during such events. Throughout each performance, the principal investigator noted sharp and maintained peaks in decibel levels with the appearance of each performer. These peaks seemed to coincide with a noticeable increase in crowd noise and varied
671
with the genre of music. It appeared that the younger audiences attending the pop show tended to yell and whistle more as the artists took the stage and as a new song would begin. Although not specifically monitored, this appeared to be the reason for the volume spikes, and future studies should address this issue. Overall crowd yelling and screaming was also observed by the principal investigator to be lower during the heavy metal performance because more fans were participating in the mosh pits and were therefore not contributing to crowd noise. Mosh pits are defined as “a descendant of punk slamdancing involving seething masses of people crashing into one another in front of the stage”11 and are more frequent in the heavy metal genre. As shown in Table 2 and graphically in Figure 2, average SPLs ranged from 95.12 dBA to 106.84 dBA during all 3 concerts and maximum-recorded SPLs did reach 125.6 dBA during the pop concert. Although some small differences are observed by location and concert type (ie, music genre), statistical calculations were not performed because of the small number of concerts used in this study. Recorded SPLs in all locations did exceed levels known to be hazardous to hearing; thus, the perception that being in the back of a concert venue protects the listener from the noise level may be incorrect. The ear plugs used in the study are highly marketed to concertgoers and have a NRR rating of 21. This implies a reduction of 21 dB SPL under laboratory conditions with proper usage and is about average for the most common, commercially available, ear plugs in use today. Although commercially available ear plugs cite NRR rating as guides to their effectiveness at attenuating sound, much research has shown the actual real-world attenuation of most ear plugs to be less than that indicated by the packaging. Berger et al12,13 summarized these data, and results indicated that the laboratory measurements of atten-
Figure 3 Heavy metal concert time history. Leq, equivalent sound level, the level of a constant sound that in a given time period has the same energy as does a time-varying sound; Max, maximum (A) weighted noise level; Peak, maximum unweighted noise level.
672
Otolaryngology–Head and Neck Surgery, Vol 134, No 4, April 2006
uation, as in NRR, do not provide an accurate indicator of the absolute level of sound attenuation offered to the wearer of the tested devices. In addition, Berger et al have also shown the presence of wide variability in the average realworld NRRs for insert and semi-insert devices. They showed as a percentage of laboratory values, real-world results varied from 8% to 56% (averaging 26%) depending on the individual device being tested.14 Therefore, even with the usage of commercially available hearing protection devices, the protection offered may in fact be less than expected, complicating device selection and usage. As shown in Table 5, 9 of 14 participants not wearing earplugs had significant threshold shifts under all 3 method criteria. In contrast, only 4 of 15 individuals using ear plugs showed significant threshold shifts. Three of those individuals were identified by the OSHA STS criterion; all 4 were identified by ASHA and the multinomial model criteria. Thus, although not universally effective, ear plug usage offered protection to those that used them. One possible explanation as to why the ear plugs were not universally effective could be related to fit. Although every effort was made to instruct participants in the correct usage of the ear plugs, variation in the physical size of each person’s external auditory canal may have affected the fit of the plastic flanges on the plugs. During the recruitment portion of the study, it became evident to the study recruiter that there was an aversion to the use of ear plugs in the concert going community. In fact, during 1 performance setup, 2 participants refused and were replaced by alternates to take front row seats to the sold out concert if they were selected to wear ear plugs. Another participant refused to wear ear plugs immediately before being seated during the first concert, resulting in that participant’s exclusion from the study and resulting in an odd number of subjects at the soundboard position. Interestingly, although, as shown earlier, there is a large degree of resistance toward the use of ear plugs, the causes of such resistance are varied. A frequently cited reason is the noise reduction offered by the ear plug is perceived by the user to interfere with or distort the sounds the wearer wishes to hear.14 During this study, no specific reasons were given by the participants who refused to use ear plugs and in fact 1 participant stated that the music had less distortion and even sounded better with the use of the ear plugs. Herberg et al15 in 1984 interviewed 210 workers in the metal-working, mining, and textile industries and cited reasons for lack of hearing protection as subjective tolerance to noise, concern for hearing protection interfering with communication, machine operation, and a feeling of isolation created by hearing protection equipment. It was also found that wearers of hearing protection disliked the subjective aural and tactile sensations of the devices, they were influenced by peer pressure, and there was in general a lack of concern for future consequences.15 Although not specifically determined in this study, it is likely these reasons had
some influence on whether a participant refused to wear the ear plugs. Although the OSHA protects employees from hazardous working environments, there is no such protection for the amusement seeking public.6 Therefore, concertgoers are left to their own judgment as to when ear plugs should be used. As mentioned previoulsy, the intense resistance to their use limits the number of people who chose to do so despite the potential for hearing loss. One of the major weaknesses of this study is the small sample size. Only 29 people tested and 3 concerts were observed because of limited availability of tickets and concert performers willing to participate. In addition, follow-up audiograms were not obtained because of participants being unwilling to return for testing without compensation. Both of these problems pose significant challenges to studies looking at real-world concert environments and will need to be addressed if additional information is to be gained regarding the concert environment. Furthermore, although it can be seen in Figure 3 that sound levels were fairly constant over the entire duration of the performances, Leq, which is just a simple average of the measure sound level, does not represent the real risk because the exposure levels in the concert venue fluctuate slowly and are maintained at high levels for prolonged periods. This places concert goers at higher risk for hearing loss than a simple average Leq would predict. Future investigations should address this issue to provide a more realistic estimate of an attendees risk for hearing loss. As shown by this study, questions abound regarding the safety and impact of the concert environment on a person’s hearing. Future studies should compare different ear plugs to determine which offers the most protection, including varying NRR ratings and the use of commercially available as opposed to custom-made ear plugs. Issues regarding crowd noise should be better understood and measured to assess the total noise in a concert venue, not just that limited to the output from the speakers. Other protective measures should be tested such as the pre-exposure treatment of attendees with antioxidant vitamins to determine their effect on SHTS.
CONCLUSIONS Modern concert environments are often excessively loud because of the output from the speakers and the noise generated by those in attendance. Although earplugs are in fact helpful, the decibel levels obtained in this study and the possible reduced real-world sound attenuation of ear plugs indicate the potential for significant hearing loss in concertgoers. Although misconceptions abound, SPLs appear equally concerning in all parts of the venue and across music genres. Therefore, everyone in attendance is at risk. Furthermore, crowd noise likely increases a person’s risk of temporary threshold shifts, and future studies are needed to determine
Opperman et al
Incidence of spontaneous hearing threshold shifts . . .
the best methods for hearing protection in the modern concert environment. Above all, concertgoer attitudes toward hearing protection and the use of ear plugs need to change in order to protect the concert-going community. This study did not examine the effect of recurrent temporary threshold shifts resulting in permanent shifts.
REFERENCES 1. Hunter LL, Ries DT, Schlauch RS, et al. Safety and clinical performance of acoustic reflex tests. Ear Hear 1999;20:506 –14. 2. OSHA 1983 Occupational noise exposure: Hearing conservation amendment, Occupational Safety and Health Administration, 29 CFR 1910.95; 48 Federal Register, 9738-9785. 3. Ward WD, Royster JD, Royster LH. Auditory and nonauditory effects of noise. In: Berger EH, Royster LH, Royster JD, et al, editors: The Noise Manual (ed 5). AIHA Press; 2000;123– 47. 4. NIOSH (1998) Criteria for a recommended standard: occupational noise exposure: Revised Criteria, National Institute for Occupational Safety and Health, U.S. Department of Health and Human Services Report DHHS (NIOSH) 98-126, Cincinnati, OH.
673
5. Todd, Neil P. McAgnus. Vestibular responses to loud dance music: a physiological basis of the ‘rock and roll threshold’? J Acoust Soc Am 2000;107:496 –500. 6. Cabot RC, Genter CR, Lucke T. Sound levels and spectra of rock music. J Audio Eng Soc 1979;27:267– 83. 7. Sataloff RT. Rock concert audience noise exposure: a preliminary study. J Occup Hear Loss 1998;1:97–9. 8. Betz CL. The dangers of rock concerts. J Pediatr Nurs 2000;15: 341–2. 9. Axelsson A, Lindgren F. Temporary threshold shift after exposure to pop music. Scand Audiol 1978;7:127–35. 10. Metrodome built on a sound basis” [North Sports Final, C Edition]. Chicago Tribune; January 20, 1992:10. 11. AltCulture (2000). Moshing [on-line]. Available at: http://www. altculture.co/.index/aentries/m/moshing.html. Accessed September, 2005. 12. Berger EH. Using the NRR to estimate the real world performance of hearing protectors. J Sound Vib 1983;17:12– 8. 13. Berger EH. Can real-world hearing protector attenuation be estimated using laboratory data? J Sound Vib 1988;22:26 –31. 14. Berger EH. Hearing protection devices. In: Berger EH, Royster JD, et al, editors: The Noise Manual (ed 5). Fairfax, VA: AIHA Press, 2000:379 – 454. 15. Herberg KW. Investigation of the motives for wearing or not wearing hearing protectors [German]. Die BG 1984;174 –177.
Did you know? You can stay up-to-date on key articles with saved searches and electronic table of contents e-mail alerts. Visit http://journal.entnet.org today to see what is new online!
ORIGINAL RESEARCH
Incidence of spontaneous hearing threshold shifts during modern concert performances David A. Opperman, MD, William Reifman, NP, PA, Robert Schlauch, PhD, and Samuel Levine, MD, Minneapolis, Minnesota
odern-day music performances often consist of long periods of high volume sound and short periods of rest between music sets. Although it is known that intense levels of noise exposure can cause irreversible damage to the hearing mechanism, regular exposure to less intense, but still noisy environments, may also involve the insidious destruction of inner-ear components that unavoidably leads to an elevation in hearing thresholds. It has been clearly understood that at low levels for long
periods of time, hearing loss will occur. Similarly, there can be a single intense loud sound that will cause a permanent hearing loss.1 These issues have been studied well and are agreed on in the literature. The development of a hearing loss caused by habitual exposure to this level of noise (noise-induced hearing loss [NIHL]) typically involves decreased hearing acuity, occurring immediately after noise exposure and lasting for a variable period of time thereafter. This is referred to as a temporary threshold shift. Although there is no clear definition of how long a temporary shift can last if this threshold shift does not recover, irreversible cochlear damage has likely occurred, resulting in a permanent threshold shift. Such permanent threshold shifts are often accompanied by other common symptoms of hearing dysfunction including tinnitus, loudness recruitment, and frequency distortion, which have significant morbidity associated with them. NIHL commonly occurs after prolonged exposure to noise greater than 85 dBA. In the workplace, OSHA (Occupational Safety and Health Act, 1983) currently has in place strict rules that limit the amount of noise exposure in order to prevent NIHL.2 These guidelines were promulgated from extensive research showing that the continued exposure to sound levels greater than 85 dBA would result in permanent hearing loss.3 Although the basis of these regulations has been challenged, general acceptance is seen in the regulatory community.4 These rules state that an individual may be exposed to 90 dBA for a maximum of 8 hours, and, as intensity increases, duration of exposure is mandated to be less. Thus, for noise of 100 dBA, exposure must be limited to 2 hours or less, and for noise of 115 dBA, exposure must be limited to 25 minutes or less (Table 1). If
From the Department of Otolaryngology-Head and Neck Surgery, University of Minnesota, 420 Delaware Street, S.E., Minneapolis, MN 55455.
Reprint requests: David A. Opperman, MD, Department of Otolaryngology, University of Minnesota, 7563 Teal Road, Woodbury, MN 55125. E-mail address: [email protected].
OBJECTIVES: Concerts have long periods of intense sound with short break intervals. Hearing concerns are well known to performers; concertgoers largely ignore them. Preperformance and postperformance audiograms were compared to assess hearing threshold shifts with and without earplugs. METHODS: A prospective, randomized study in which 29 volunteers attended 3 concerts, encompassing 3 music genres. Audiograms, seating location, sound intensity, and earplug-use data were collected. Data were analyzed to determine frequency test-retest variability. RESULTS: Sound levels averaged 99.8 dBA, and the maximum was 125.6 dBA. Sixty-four percent (9/14) of participants without earplugs showed significant threshold shifts compared with 27% (4/15) of those using earplugs. No significant differences existed between music genres or seating location. CONCLUSIONS: This study showed a high incidence of threshold shifts in unprotected concertgoers. Sound levels exceeded all Occupational Safety and Health Act rules despite standardized sound systems. A significant reduction in threshold shifts was seen with the use of earplugs. EBM rating: A-1b © 2006 American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. All rights reserved.
M
0194-5998/$32.00 © 2006 American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. All rights reserved. doi:10.1016/j.otohns.2005.11.039
668
Otolaryngology–Head and Neck Surgery, Vol 134, No 4, April 2006
Table 1 OSHA Standards for noise exposure greater than 85 dBA SPL Duration per day, hours
Sound level dBA slow
8 6 4 3 2 1.5 1 .5 .15 or less
90 92 95 97 100 102 105 110 115
there is concern that these limits may be exceeded, employees must be provided with hearing protection devices. The work place rules required by OSHA, however, do not apply to the paying concert-going community. In part, because of improved technology in sound amplification, the absence of noise regulations governing concert goers, and the idea that many individuals find loud music quite pleasurable,5 the level of noise exposure at a concert is likely to be quite significant. Various studies have found sound levels at rock concerts often to be significantly higher than 85 dBA and thus pose risk to attendants hearing. Cabot et al6 determined that the sound level at various concert venues was on average 95.3 dBA, and Sataloff7 cites peak levels at 139 dBA. Furthermore, there are studies that suggest that sound intensity at such venues may vary from 90 dBA to as high as 122 dBA.6 Also, a performance usually entails several hours of high-volume sound with several interspersed rest interludes in which the noise level may or may not significantly decrease. If levels are maintained at values greater than 85 dBA, this may (and often does) lead to exposure times that exceed the levels published by OSHA and frequent concertgoers may experience some potentially irreversible hearing loss from this experience. Although certain genres of music, such as heavy metal, with its aggressive rhythms and amplified, distorted guitars, have a reputation for being excessively loud, it is unclear whether other more mainstream genres of music played at concerts may also pose the same risk to attendants’ hearing. These hearing concerns are well known to performers; they are largely understated and ignored by concertgoers. This may have the potential to result in widespread, detrimental, although preventable, hearing loss. It has been recommended that ear plugs be worn by those attending live music concerts,8 and in 1 study that evaluated threshold shifts in performers and listeners, Axelson and Lindgren9 showed a larger degree of hearing threshold shift in the audience as compared with the performers. Despite these results, however, most concertgoers opt not to use such devices. We undertook this study to examine sound intensity levels throughout a well-known concert venue and the ef-
fectiveness of earplugs during pop, heavy metal, and rockabilly music performances. Furthermore, observations were made regarding sound levels within a venue for the duration of the concerts. Are sound intensities maintained at high levels for a time exceeding the OSHA rules? And, finally, are commercially available foam ear plugs effective in pre-
Figure 1 Venue floor plan. Red dots represent participants’ locations during concerts.
Opperman et al
Incidence of spontaneous hearing threshold shifts . . .
669
Table 2 Levels (dBA) by location within the concert venue for each music genre. Values calculated from data recorded during the duration of each concert Concert (duration in minutes) Pop (360)
Heavy metal (210)
Rock-a-billy (195)
Location
Average
Minimum
Maximum
Front Sound board Left Right Back Front Sound board Left Right Back Front Left Right Back
98.47 100.92 101.92 98.17 95.12 97.96 98.58 99.41 102.66 96.57 106.84 102.71 101.29 95.94
59.1 81.2 56.7 63.7 71.0 60.5 61.3 63.5 54.1 58.8 80.7 84.5 83.8 76.8
117.1 119.4 125.1 125.6 108.6 112.6 120.4 112.7 124.2 113.7 118.3 114.9 115.4 106.1
venting spontaneous hearing threshold shifts in concert attendees?
MATERIALS AND METHODS An agreement was reached with a popular music venue to allow this experiment to take place. Performers and the venue location are withheld as a precondition for permission to conduct the study. Twenty-nine people consisting of 14 females and 15 males, with an age distribution from 17 to 59 years, volunteered from the local concert-going community to participate in an institutional review board–approved prospective, randomized study to determine the sound intensity throughout a venue and the effectiveness of earplugs at preventing hearing-threshold shifts during 3 concerts, encompassing pop, heavy metal, and rockabilly music genre. This experimental protocol was reviewed and conducted in accordance with the institutional review board at the University of Minnesota. Each of the participants agreed to have audiograms recorded immediately before entering the venue and again immediately after the concert. These audiograms were obtained in a mobile sound booth using a Benson CCA200 automated audiometer, integrated with a sound-level meter (Benson Medical Instruments, Minneapolis, MN), factory calibrated yearly and locally before each use. Also, each participant agreed to fill out a brief medical and noise exposure history to help determine eligibility for the study. To be allowed to participate, participants had no evidence of progressive hearing loss by history and had normal/near normal hearing thresholds at the time of their preconcert audiogram. Seating assignments were randomly assigned as was whether or not a person would be wearing ear plugs. Spe-
cific seating locations were standardized by arrangement with the venue to ensure consistency within the 3 chosen concert floor plans (Fig 1). Two participants were placed in the front-row center position, 2 were placed behind the railing on the stage-right and stage-left staircase positions, 2 were seated at the soundboard, and 2 were placed at the rear of the floor seating area. At each seating location, 1 participant wore ear plugs during the entire concert performance and during all rest periods, whereas the other wore only a recording microphone and dosimeter. Each venue position was monitored for sound pressure levels (SPLs) using a dBA scale once every minute (slow) over the entire concert by way of the computer-controlled dosimeters (705 NoiseBadge; Larson Davis, Provo, UT). The selected ear plugs for this study, Mack’s Hear Plugs (McKeon Products, Inc, Warren, MI), were selected because of their marketing toward concertgoers, ease of use, and their noise reduction rating (NRR) of 21. The NRR represents the decibel attenuation provided by an earplug
Figure 2 position.
Average levels (dBA) for each concert by genre and
670
Otolaryngology–Head and Neck Surgery, Vol 134, No 4, April 2006
Table 3 After show minus before show difference in hearing levels, averaged over location and concert. Table includes mean difference and standard deviation 500 No ear plugs Ear plugs p-value (unadjusted) p-value (adjusted)*
1k
2k
3k
4k
6k
8k
2.86 (3.08) 3.04 (5.30) 5.36 (7.96) 10.18 (9.12) 11.61 (10.22) 8.46 (14.38) 3.57 (7.89) ⫺0.17 (2.75) 0.83 (2.94) 1.5 (2.96) 2.67 (7.76) 3.33 (6.17) ⫺1.00 (6.25) 0.33 (5.89) 0.010 0.186 0.107 0.024 0.043 0.043 0.219 0.011 0.214 0.118 0.019 0.038 0.38 0.291
*Adjusted for seating location and concert.
under laboratory conditions. In actual settings, OSHA considers the effective attenuation to be one half the NRR. Before each concert, all individuals randomly selected to wear ear plugs were instructed on the use and insertion of the plugs as directed by the product manufacturer by the principal investigator. Before each concert, sound output was standardized at the soundboard for a maximum level output of 105 db(A) SPL and both primary and relay sound systems were used during all 3 performances. Each system calibration was performed by the same technician, using industry standard equipment for each concert to maintain a standard for data collection.
RESULTS Table 2 summarizes the SPL on a dBA-weighted scale for the 3 examined music genres. Average levels were calculated from 1-minute interval recordings across the entire duration of each concert performance. The minimum and maximum values represent the highest and lowest values during each concert and thus define the SPL range. Graphical illustration of the average levels (dBA) for each concert is shown in Figure 2. A hearing-shift value was calculated using the after show minus before show differences in hearing threshold levels by frequency, averaged over seating location and concert. These are shown in Table 3. The after minus before show differences in hearing were averaged over the right and left
ear for each frequency and univariate analysis showed no significant difference between seating locations and concert. An overall analysis that evaluates all the frequencies simultaneously (repeated measures analysis of variance) showed a significant effect for earplugs (F1 ⫽ 8.83, P ⫽ 0.006) with no significant interaction between earplugs and frequencies. Individual audiograms were evaluated for significant threshold shifts using 3 methods: OSHA standard threshold shift (STS) criterion, ASHA (1994) criterion, and a multinomial statistical model. The OSHA STS criteria requires a 10-dB or greater change for a pure-tone average based on thresholds obtained from 2,000, 3,000, and 4,000 Hz. The ASHA (1994) criteria look for a decrease of hearing sensitivity of 20 dB or greater at any one frequency, a decrease of 10 dB or more at any 2 adjacent frequencies, or the loss of response at 3 or more consecutive frequencies where responses were previously obtained. The multinomial model examined whether a particular audiometric configuration on retest was likely to occur by chance alone. Multinomial probabilities were calculated based on the SD of intertest differences (5 dB) and the number of thresholds being measured in ear tested ear. Table 4 summarizes the number of individual ears that showed a threshold shift by each specific criterion and by the use or lack of earplugs. Table 5 shows the number of participants who showed a threshold shift in either one or both ears by each method. At the completion of each concert, time history plots were created to help explain visually the sound levels obtained across the entire length of each performance. An example of this is represented in Figure 3.
Table 4 Number of individual ears that demonstrated a threshold shift by specific criteria and by the use, or lack of earplugs Left ear
Ear plug No ear plugs
Significant threshold shift No threshold shift Significant threshold shift No threshold shift
Right ear
OSHA STS
ASHA
Multinomial
OSHA STS
ASHS
Multinomial
3 12 8 6
4 11 8 6
4 11 8 6
1 14 6 8
1 14 7 7
1 14 7 7
Opperman et al
Incidence of spontaneous hearing threshold shifts . . .
Table 5 Number of participants who demonstrated a threshold shift in either one or both ears by each method criteria OSHA STS
ASHA
Multinomial
3 9
4 9
4 9
Plugs No plugs
DISCUSSION With the vast array of concerts that tour in a given year, it is not surprising that a large number of people have been or will be concertgoers. What is surprising is that the vast majority of people attending these performances are unaware of the potential impact that the noise levels to which they will be exposed could have on their hearing. This study attempted to look at a single venue during 3 concerts of different music types to understand the concert environment better. What seemed an obvious prestudy question, namely, is music played at very high volumes at most concerts, only scratched the surface of the information gained. The new questions that arose form the results of the study. The concerts observed during this study ranged in duration from 195 minutes to 360 minutes, and the average SPLs were maintained above the recommended OSHA standard of 85 dBA over the entire course of each performance. Thus, even if the levels did not exceed 90 dBA, which they universally did, an attendee should only be exposed to this level of noise for a total of 120 minutes without the use of ear plugs. During performances in large indoor concert halls or outdoor venues, bands may employ the use of amplification equipment totaling upward of 500,000 W.6 Subsequently, noise levels can be excessive, as shown in this study, and hearing protection should be worn by all in attendance. In this study, all concerts had soundboard output standardized to 105 dBA. This would seem to indicate that output should be the same regardless of the music genre, which was in fact observed. Therefore, the misconception that one genre of music is louder than another may mislead concertgoers into feeling that the use of hearing protection is unnecessary at some concerts, thereby exposing them to unnecessary risk of hearing loss. Furthermore, crowd noise can be substantial even in large venues as shown by official recordings at the Metrodome in Minneapolis, MN, during the 1987 World Series. During that game, decibel recordings peaked at 125 dB, a level beyond the threshold for pain and louder than a 727 jet taking off 300 yards away.10 Despite this, few people wear hearing protection during such events. Throughout each performance, the principal investigator noted sharp and maintained peaks in decibel levels with the appearance of each performer. These peaks seemed to coincide with a noticeable increase in crowd noise and varied
671
with the genre of music. It appeared that the younger audiences attending the pop show tended to yell and whistle more as the artists took the stage and as a new song would begin. Although not specifically monitored, this appeared to be the reason for the volume spikes, and future studies should address this issue. Overall crowd yelling and screaming was also observed by the principal investigator to be lower during the heavy metal performance because more fans were participating in the mosh pits and were therefore not contributing to crowd noise. Mosh pits are defined as “a descendant of punk slamdancing involving seething masses of people crashing into one another in front of the stage”11 and are more frequent in the heavy metal genre. As shown in Table 2 and graphically in Figure 2, average SPLs ranged from 95.12 dBA to 106.84 dBA during all 3 concerts and maximum-recorded SPLs did reach 125.6 dBA during the pop concert. Although some small differences are observed by location and concert type (ie, music genre), statistical calculations were not performed because of the small number of concerts used in this study. Recorded SPLs in all locations did exceed levels known to be hazardous to hearing; thus, the perception that being in the back of a concert venue protects the listener from the noise level may be incorrect. The ear plugs used in the study are highly marketed to concertgoers and have a NRR rating of 21. This implies a reduction of 21 dB SPL under laboratory conditions with proper usage and is about average for the most common, commercially available, ear plugs in use today. Although commercially available ear plugs cite NRR rating as guides to their effectiveness at attenuating sound, much research has shown the actual real-world attenuation of most ear plugs to be less than that indicated by the packaging. Berger et al12,13 summarized these data, and results indicated that the laboratory measurements of atten-
Figure 3 Heavy metal concert time history. Leq, equivalent sound level, the level of a constant sound that in a given time period has the same energy as does a time-varying sound; Max, maximum (A) weighted noise level; Peak, maximum unweighted noise level.
672
Otolaryngology–Head and Neck Surgery, Vol 134, No 4, April 2006
uation, as in NRR, do not provide an accurate indicator of the absolute level of sound attenuation offered to the wearer of the tested devices. In addition, Berger et al have also shown the presence of wide variability in the average realworld NRRs for insert and semi-insert devices. They showed as a percentage of laboratory values, real-world results varied from 8% to 56% (averaging 26%) depending on the individual device being tested.14 Therefore, even with the usage of commercially available hearing protection devices, the protection offered may in fact be less than expected, complicating device selection and usage. As shown in Table 5, 9 of 14 participants not wearing earplugs had significant threshold shifts under all 3 method criteria. In contrast, only 4 of 15 individuals using ear plugs showed significant threshold shifts. Three of those individuals were identified by the OSHA STS criterion; all 4 were identified by ASHA and the multinomial model criteria. Thus, although not universally effective, ear plug usage offered protection to those that used them. One possible explanation as to why the ear plugs were not universally effective could be related to fit. Although every effort was made to instruct participants in the correct usage of the ear plugs, variation in the physical size of each person’s external auditory canal may have affected the fit of the plastic flanges on the plugs. During the recruitment portion of the study, it became evident to the study recruiter that there was an aversion to the use of ear plugs in the concert going community. In fact, during 1 performance setup, 2 participants refused and were replaced by alternates to take front row seats to the sold out concert if they were selected to wear ear plugs. Another participant refused to wear ear plugs immediately before being seated during the first concert, resulting in that participant’s exclusion from the study and resulting in an odd number of subjects at the soundboard position. Interestingly, although, as shown earlier, there is a large degree of resistance toward the use of ear plugs, the causes of such resistance are varied. A frequently cited reason is the noise reduction offered by the ear plug is perceived by the user to interfere with or distort the sounds the wearer wishes to hear.14 During this study, no specific reasons were given by the participants who refused to use ear plugs and in fact 1 participant stated that the music had less distortion and even sounded better with the use of the ear plugs. Herberg et al15 in 1984 interviewed 210 workers in the metal-working, mining, and textile industries and cited reasons for lack of hearing protection as subjective tolerance to noise, concern for hearing protection interfering with communication, machine operation, and a feeling of isolation created by hearing protection equipment. It was also found that wearers of hearing protection disliked the subjective aural and tactile sensations of the devices, they were influenced by peer pressure, and there was in general a lack of concern for future consequences.15 Although not specifically determined in this study, it is likely these reasons had
some influence on whether a participant refused to wear the ear plugs. Although the OSHA protects employees from hazardous working environments, there is no such protection for the amusement seeking public.6 Therefore, concertgoers are left to their own judgment as to when ear plugs should be used. As mentioned previoulsy, the intense resistance to their use limits the number of people who chose to do so despite the potential for hearing loss. One of the major weaknesses of this study is the small sample size. Only 29 people tested and 3 concerts were observed because of limited availability of tickets and concert performers willing to participate. In addition, follow-up audiograms were not obtained because of participants being unwilling to return for testing without compensation. Both of these problems pose significant challenges to studies looking at real-world concert environments and will need to be addressed if additional information is to be gained regarding the concert environment. Furthermore, although it can be seen in Figure 3 that sound levels were fairly constant over the entire duration of the performances, Leq, which is just a simple average of the measure sound level, does not represent the real risk because the exposure levels in the concert venue fluctuate slowly and are maintained at high levels for prolonged periods. This places concert goers at higher risk for hearing loss than a simple average Leq would predict. Future investigations should address this issue to provide a more realistic estimate of an attendees risk for hearing loss. As shown by this study, questions abound regarding the safety and impact of the concert environment on a person’s hearing. Future studies should compare different ear plugs to determine which offers the most protection, including varying NRR ratings and the use of commercially available as opposed to custom-made ear plugs. Issues regarding crowd noise should be better understood and measured to assess the total noise in a concert venue, not just that limited to the output from the speakers. Other protective measures should be tested such as the pre-exposure treatment of attendees with antioxidant vitamins to determine their effect on SHTS.
CONCLUSIONS Modern concert environments are often excessively loud because of the output from the speakers and the noise generated by those in attendance. Although earplugs are in fact helpful, the decibel levels obtained in this study and the possible reduced real-world sound attenuation of ear plugs indicate the potential for significant hearing loss in concertgoers. Although misconceptions abound, SPLs appear equally concerning in all parts of the venue and across music genres. Therefore, everyone in attendance is at risk. Furthermore, crowd noise likely increases a person’s risk of temporary threshold shifts, and future studies are needed to determine
Opperman et al
Incidence of spontaneous hearing threshold shifts . . .
the best methods for hearing protection in the modern concert environment. Above all, concertgoer attitudes toward hearing protection and the use of ear plugs need to change in order to protect the concert-going community. This study did not examine the effect of recurrent temporary threshold shifts resulting in permanent shifts.
REFERENCES 1. Hunter LL, Ries DT, Schlauch RS, et al. Safety and clinical performance of acoustic reflex tests. Ear Hear 1999;20:506 –14. 2. OSHA 1983 Occupational noise exposure: Hearing conservation amendment, Occupational Safety and Health Administration, 29 CFR 1910.95; 48 Federal Register, 9738-9785. 3. Ward WD, Royster JD, Royster LH. Auditory and nonauditory effects of noise. In: Berger EH, Royster LH, Royster JD, et al, editors: The Noise Manual (ed 5). AIHA Press; 2000;123– 47. 4. NIOSH (1998) Criteria for a recommended standard: occupational noise exposure: Revised Criteria, National Institute for Occupational Safety and Health, U.S. Department of Health and Human Services Report DHHS (NIOSH) 98-126, Cincinnati, OH.
673
5. Todd, Neil P. McAgnus. Vestibular responses to loud dance music: a physiological basis of the ‘rock and roll threshold’? J Acoust Soc Am 2000;107:496 –500. 6. Cabot RC, Genter CR, Lucke T. Sound levels and spectra of rock music. J Audio Eng Soc 1979;27:267– 83. 7. Sataloff RT. Rock concert audience noise exposure: a preliminary study. J Occup Hear Loss 1998;1:97–9. 8. Betz CL. The dangers of rock concerts. J Pediatr Nurs 2000;15: 341–2. 9. Axelsson A, Lindgren F. Temporary threshold shift after exposure to pop music. Scand Audiol 1978;7:127–35. 10. Metrodome built on a sound basis” [North Sports Final, C Edition]. Chicago Tribune; January 20, 1992:10. 11. AltCulture (2000). Moshing [on-line]. Available at: http://www. altculture.co/.index/aentries/m/moshing.html. Accessed September, 2005. 12. Berger EH. Using the NRR to estimate the real world performance of hearing protectors. J Sound Vib 1983;17:12– 8. 13. Berger EH. Can real-world hearing protector attenuation be estimated using laboratory data? J Sound Vib 1988;22:26 –31. 14. Berger EH. Hearing protection devices. In: Berger EH, Royster JD, et al, editors: The Noise Manual (ed 5). Fairfax, VA: AIHA Press, 2000:379 – 454. 15. Herberg KW. Investigation of the motives for wearing or not wearing hearing protectors [German]. Die BG 1984;174 –177.
Did you know? You can stay up-to-date on key articles with saved searches and electronic table of contents e-mail alerts. Visit http://journal.entnet.org today to see what is new online!