Thomas R. Zalewski, PhD, is an associate professor of audiology in the Department of Audiology and Speech Pathology at Bloomsburg University, Bloomsburg, Pa, and Francis X. Baur, AuD, is the owner of Amplified Hearing LLC, located in Hanover Township, Pa.

Is the preferred listening level (PLL) of an audio device attached to a noise-cancellation headset influenced by white noise? Ear canal sound pressure level (SPL) measurements were obtained to compare the PLL settings in quiet and in 85 dBA white noise. The current research found significantly higher PLLs when listening to the audio component in the presence of white noise. The use of a noise-cancellation device in ambient noise may not allow safe use of an attached audio device due to the increase in PLL, which may be dependent on the duration of listening.

Headphones with noise-cancellation technology are marketed to the consumer based on the premise that background noise can be attenuated to allow comfortable and safe listening to an attached audio component. Since noise-cancellation technology is a relatively new addition to listening devices, minimal research is available on this topic. The use of a noise-cancellation device in ambient noise may not be safe if the preferred listening level (PLL) is set to a hazardous level and/or the duration of listening places the user at risk for auditory damage.

Noise-induced hearing loss (NIHL) is the second most common form of acquired hearing impairment,1 following age. According to the National Institute on Deafness and Other Communication Disorders (NIDCD), 22 million Americans suffer from NIHL to some degree. NIHL refers to hearing loss due to extended exposure to sounds at or above 85 decibels (dB) that can damage the structures of the inner ear.2

Noise-induced hearing loss due to excessive exposure to music via various headsets and listening devices has become a topic of interest, at the forefront of hearing conservation. Campaigns have been developed to raise awareness of the risk levels these devices present to hearing health.3 While previous research has found that the number of consumers listening to audio devices at unsafe levels may be as low as 5% to 25%,4-7 it is this portion of the listening public that needs to be educated in terms of hearing conservation.3 It has also been shown that people with prior noise-exposure education rank hearing loss as a greater health problem than those not exposed to the education,8 adding to the need for increased information available on noise-cancellation devices with attached audio components.

In 2005, Chung et al8 surveyed teens and adolescents and found that only 8% of the respondents felt hearing loss is a “very big problem.” Interestingly, the respondents who had previous education regarding the risks of noise exposure ranked hearing loss much higher than those respondents with no prior noise-exposure education.

A goal of the current study is to increase the available knowledge and to educate the public regarding the risk of music-induced hearing loss.

How Loud Is Your Music? Preferred Listening Levels and Portable Music

Preferred listening levels continue to be researched as ownership of MP3 players and iPods has dramatically increased. Hodgetts, Rieger, and Szarko9 investigated the effect of different environments on the PLLs chosen by participants using different types of headphones. The study found that PLLs increased in the presence of ambient noise using MP3 music players, with in-the-ear, over-the-ear, and over-the-ear with noise reduction style headphones. While the study included headphones with noise reduction technology, noise-cancellation devices specifically were not investigated, and it is not known if these devices will allow users to set PLLs at safe listening levels.

Several studies10,11 indicate that the number of people listening at dangerous exposure levels is small in comparison to those listening at safe levels. Lee et al10 asked 16 participants to set their personal listening device to a preferred maximum listening level for 3 hours then measured temporary threshold shift (TTS). Results determined that 37% of the participants experienced a TTS of 10 dB or more in at least one frequency. The output of the headset for these participants averaged 92 dBSPL. One participant experienced a shift of 35 dB in the right ear at one frequency. The output of the headset for this participant was 104 dBSPL. In such cases, users of personal listening devices are placing their auditory systems at risk for permanent damage.

The PLLs of personal cassette players (PCPs) were examined in individuals commuting to and from work.7 The volume levels of the PCPs were set by the commuters and the headsets were placed on KEMAR in the presence of 73.2 dBA background noise. The measured continuous noise level under the headphones averaged 86.1 dBA. This study also found that the duration of exposure ranged from 40 minutes to 13 hours per day.7 The PLL coupled with the extended listening duration will place the user at risk for hearing loss.

In 1974, Kuras and Findlay12 investigated the most-comfortable level (MCL) and uncomfortable level (UCL) of study participants who were 18 to 25 years old. Of the 25 participants, 10 exceeded 100 dBA and 2 neared a level of 122 dBA. Incidence rates of listening at unsafe levels have ranged from 5% to 41%.4,6

TABLE 1. NIOSH Permissible Noise Exposures. Note: dBA=decibel level using the A-weighted scale (NIOSH, 1988).

The unchanging listening habits of individuals who use personal listening devices and tens of millions of annual sales of iPods alone3 increase the need for consumer awareness of the potential dangers of these devices. The Occupational Safety and Health Administration (OSHA)13 has designated 85 dB time weighted average (TWA) as its “threshold of action.” That is, exposure to sound levels in excess of 85 dB TWA can result in permanent cochlear damage if the exposure time exceeds the permissible levels (Table 1). Permanent metabolic cochlear damage occurs when the hair cells within the cochlea swell from being exposed to excessive levels of sound, causing a possible metabolic disruption in the physical orientation of the hair cells in relation to the tectorial membrane.

The comparison of music to noise exposure has become a topic of interest. Fligor15 compared orchestral musicians to the American National Standards Institute (ANSI) Standard S3.44,16 which predicts noise-induced permanent threshold shift (NIPTS) for individuals exposed to industrial noise. The audiogram for the violinists was found to exhibit a notch at 3 to 4 kHz, which is similar to the predicted NIPTS for industrial noise after 35 years of exposure. Therefore, music has the potential of producing auditory system damage similar to industrial noise.

Comparison of music to noise has been done repeatedly in previous research5-7,17 by calculating the exposure in terms of TWA using the measured level and the actual exposure time.7 The output levels of music from different genres were compared with the output level of white noise by Fligor and Cox.17 Results indicated that the output of white noise closely resembled the output of the selections of music from the rock, country, and adult contemporary genres, while it slightly overestimated the outputs of jazz and classical music samples.

Awareness regarding excessive noise exposure is important for consumers with no prior noise-exposure education,8 which includes the consumer purchasing noise-cancelling headsets. Do ambient sounds influence the PLLs and negate the benefit of these devices? The outcome of this research could alter the recommendation and use of noise-cancellation technology with an attached audio component in presence of ambient sounds.

Study Methods

A total of 26 females and 4 males (median age: 22.87 years; SD=1.28) underwent an evaluation consisting of otoscopy, tympanometry, air conduction puretone testing, and real-ear measurement. The inclusion criteria consisted of an unoccluded external auditory meatus, intact tympanic membrane, normal hearing, and normal middle ear function.

All participants who met the inclusion criteria were seated in a chair facing away from an Audioscan Verifit system to prevent any visual cues that could bias listening levels. A probe tube attached to the Verifit system was placed 31 mm from the tip for an adult male, and 28 mm for an adult female, into the ear canal. These probe-tube lengths represent the length of the average male and female ear canal. The probe tube length indicator was placed at the intratragal notch of the ear to ensure appropriate placement.18

White noise produced by the Virtual Audiometer 1.1 computer program was presented via the speaker system into the soundfield of the test room at a distance of approximately 1 meter from the participant. The level of the white noise was set at 85 dBA. The reference microphone from the real ear system verified the uniformity of white noise level for the participants at the level of the ear. Measurements of the sound pressure level in the external auditory canal (EAC) of both ears individually were taken by the probe tube attachment to determine the real-ear unaided gain (REUG).19

The white noise was removed from the soundfield, and the audio component was attached to the Bose Quiet Comfort2 Noise-Cancelling Headphones. The researcher controlled the volume of the audio device to prevent the participants from setting the device at similar levels. The volume was started from zero and the researcher adjusted the volume until the PLL was attained. The song How You Remind Me by Nickelback from their Silver Side Up LP (2001) was chosen as a representative of the rock musical genre based on research by Fligor and Cox.17 The rock musical genre was found to have the highest peak dBSPL levels in a study of various PCPs with different headphones.17 A 30-second segment of the song was presented to the participant, beginning at the 28-second mark of the song, chosen as the sample starting point due to the full participation of the electric guitars, percussion, and vocals. The probe-tube attachment measured the sound pressure level in dBA in both EACs individually. The most consistent EAC sound level, as judged by one of the authors during the 30-second segment, was deemed the recorded PLL value.

The volume of the audio component was reduced back to zero, and the white noise was reintroduced at 85 dBA. Again, the reference microphones of the real ear attachment verified the white noise intensity level. The PLL was reestablished, and the EAC SPL PLL with the white noise was measured by following the same procedures used to determine the EAC SPL without white noise. The PLLs with and without noise and starting ear were counterbalanced for each participant to remove any order effect. A post-test air conduction audiogram was obtained and compared to the pre-test audiogram to determine if a standard threshold shift (STS) occurred.

Measurements in the ear canal were taken in dBA by the Audioscan Verifit system. The output levels of the two sounds, the music and the white noise, were found to be similar by prior research.17 This allows for an accurate conversion by subtracting the difference between these readings, the transfer function, from the measured PLL levels for comparison to the NIOSH damage-risk criteria. A Multivariate Analysis of Variance (MANOVA) was performed with an alpha level of .05 to determine if the preferred listening levels of the noise-cancellation headsets with an audio component in white noise and in quiet were significantly different.

FIGURE 1. PLLs of audio component with and without 85 dB of white noise present.

Results

Results of this research indicate that the mean PLLs increased more than 9 dBA when noise was introduced at a level of 85 dB (Figure 1). The recorded mean PLLs and their standard deviations are found in Table 2. Standard deviations were consistent among ears with and without noise. MANOVA statistical analysis identified a significant increase in PLL with the addition of noise in dBA (F=41.230; df 1, 116; P < 0.0001). The analysis did not identify a significant difference when comparing ears in dBA (F=1.032; df 1, 116; P=0.312), as well as no significance when comparing noise and ears in both dBA (F=0.033; df 1, 116; P=0.857).

TABLE 2. The personal listening levels (PLLs) of the study subjects recorded in dBA in quiet and the presence of 85 dBA white noise. Notes: dBA=A-weighted scale; Ear=ear tested; M=mean; SD=standard deviation; N=number of trials.
TABLE 3. Gender comparison of personal listening levels (PLL) with and without noise. Notes: dBA=A-weighted scale; Difference=difference between male and female results.

The gender makeup of the participation group consisted of 26 females and 4 males. The PLLs in noise and without noise of the two groups are shown in Table 3. Males chose a higher PLL in all four settings. The average PLL for the male participants was as much as 15 dB greater than the average of the female participants.

Air conduction thresholds were tested before and after the experimental conditions. The participants’ average thresholds are shown in Table 4. None of the participants experienced a TTS during the testing period.

Discussion

The purpose of this study was to determine if the PLL of an audio device attached to a noise-cancellation headset is influenced by white noise. Statistical analysis indicated that the presence of the noise in the environment influenced the PLL setting of the noise-cancellation headset.

The PLLs of the participants listening to an attached audio component in the presence of white noise were found to be 85.52 dBA for the combined ears. The participants were exposed to this level for approximately 3 minutes; however, consumers targeted by this research for education and awareness are listening at durations longer than 3 minutes. It has been found that nearly 88% of individuals using an iPod listen at least 1 hour per day, with approximately 10% listening 5 to 8 hours per day.20 Therefore, there is a potential of individuals using noise-cancellation systems for durations that could damage their auditory systems.

TABLE 4. Pre- and post-experiment conditions relative to average puretone air conduction thresholds. Notes: Average=both ears combined; Pre-Screening=air conduction thresholds pre-noise exposure; Post-Screening=air conduction thresholds post-noise exposure.

The findings of the current research have similarities with prior research. Rice, Breslin, and Roper11 found that 25% of their study participants listened to levels of 90 dBA and 5% listened to levels of 100 dBA. A follow-up study conducted by Rice, Rossi, and Olina6 found only 10% listened at a daily noise exposure level of at least 87 dBA.

The current research found that 16.6% of the participants set their PLL at a level of 90 dBA or more, while no participant set their PLL at or above 100 dBA. This may indicate that users of personal listening devices are setting the volumes at a slightly lower level than found in the study from 20 years ago.11

Rice, Rossi, and Olina6 concluded that, although a risk for auditory damage exists, the percentage of the listening population exposed was not significant. The current research found that, although the percentage of users setting their PLLs at the dangerous exposure levels of 90+ dBA has slightly declined, the number of users setting their PLLs just below this level—at 87 dBA—has dramatically increased from 10% to 40%.

Although 87 dBA is not extremely high, it does place the auditory system of the listener at risk for damage if the device is used for extended periods of time. This may occur during air travel or when traveling for an extended period of time by automobile. The current study looked at PLLs for a short duration of listening, and it cannot be stated if the listener will increase the PLL over time as the auditory system fatigues, which would increase the risk of damage to the system.

The selection of music was chosen due to previous inclusion in noise-related research as a representative of the rock musical genre. The rock musical genre was found to have the highest peak dBSPL levels in a study of various PCPs with different headphones,17 leading to a “worse case” scenario.

Future research measuring PLLs for different musical genres in the presence of different levels of background noise is needed. This will allow users to make informed decisions concerning the types of environments to use the device, the duration of device use, as well as if the genre of music influences the PLL.

The participants of this study may not truly represent the users of noise-cancellation technology. Gender of the participants included 26 females and 4 males; additionally, 29 of the 30 participants were Caucasian. Future research using participants from other ethnic backgrounds and age groups will allow generalization of the findings to a more diverse population.

The March 2006 HR  is dedicated to music-induced hearing loss and hearing aids for audiophiles, and the March 2007 HR  takes on the issue of occupational hearing conservation and hearing protection. Both are available in the HR Archives.

Previous research by Catalano and Levin4 showed that males exceed permissible exposure limits more than females. Their results reported that 29.2% of females versus 41.2% of males exceeded 100% of the permissible exposure level when compared to the OSHA 90 dBA TWA standard. The male participants in the current study had a PLL of 15 dBA higher than the females without noise and 7.41 dBA higher with noise when listening to the attached audio component. These values should be interpreted with caution due to the limited number of male participants (4 subjects or 13% of participants). However, this corresponds to the research by Catalano and Levin4 who found higher PLLs for males resulting in higher noise-dose levels leading to reduced safe listening times. To validate this finding, future research should include a greater number of male participants.

Conclusions

The current research found the use of an audio component attached to a noise-cancellation headset resulted in significantly higher PLL in the presence of background noise. While this may allow for comfortable listening to the audio component, safe listening may be in jeopardy due to the higher PLL.

Hearing care professionals and consumers should be aware of this increased risk of hearing loss. Noise-cancelling headphones do provide the opportunity for safer listening to an attached audio component in the presence of noise (compared with an audio device without this technology). Hearing care professionals should advocate the use of this technology for consumers interested in using a noise-cancellation device with the attachment of an audio component in the presence of excessive noise.

However, the recommendation of the use of an attached audio component to a noise-cancellation system is dependent upon the chosen level PLL, the intensity of the ambient noise, and the duration of use. Consumers and hearing professionals need to be made aware that the potential does exist for dangerous exposure levels when using an audio component attached to a noise-cancellation headset in everyday listening environments if the PLL intensity exceeds 85 dBA.

Correspondence can be addressed to HR at [email protected] or Thomas R. Zalewski, PhD, at .

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