ipod Noise Exposure Assessment in Simulated Environmental Conditions

Transcription

1 ipod Noise Exposure Assessment in Simulated Environmental Conditions Kyle N. Acker Advised by: Robert Novak Michael Heinz

2 Background Since the 80s and the invention of the personal audio player, there have been studies into the effects of exposure to noise from these devices Previous studies have shown that personal audio players have the ability to exceed levels that are known to be damaging to hearing (>130dBA), the coupling of the transducer to the ear affects the sound pressure level in the ear canal, and that extended listening times are occurring. Lee (1985) found that in a study of personal audio device users under normal listening conditions at their maximum level, 7 of the 18 users experienced temporary threshold shifts >10dBHL which returned to normal after 24 hours of non-use.

3 Background Airo (1996) found that there is a correlation between the level that a user listens to their personal audio device and the amount of background noise. The average listening level of their subjects was 82dBSPL. However, in background noise that exceeded 72dBSPL, the overall volume of the player exceeded 85dBSPL. This, coupled with extended listening times, could be a source for noise induced hearing loss. Florentine, et.al. (1998) even found that maladaptive behaviors are seen in people that listen to excessive loudness show patterns similar to that of substance abusers with illicit substances.

4 Noise Standards The Occupational Safety and Health Act (OSHA) states that anyone experiencing exposure to noise levels > 85 dba is entered into a hearing conservation program 90dBA for 8 hours = 100% dose of allowable noise for a 24 hour period; 95dBA for 4 hours = 100% dose 100dBA for 2 hours= 100% dose, etc American Conference of Governmental Industrial Hygienists (ACGIH) follows a similar plan with an 85dB action level and a 3dB exchange rate. Time-weighted Average Intensity Level - dba OSHA ACGIH Hours of Exposure

5 Questions Does the potential exist/is it realistic that digital audio players can cause noise induced hearing loss in college students? Do different environmental noises have an effect on the comfortable listening level of a digital audio player in college students (main effect)? Does a change in the level of environmental noise have an effect on comfortable listening level of a digital audio player in college students(main effect)? Does the coupling of the earbud to the ear have and effect on comfortable listening level of a digital audio player in college students (main effect)? Are there any significant interactions between preferred listening levels and environment by earphone style?

6 Materials & Methods Subjects 9 college students that listen to their ipod or similar digital audio device for at least 3 hours per week. 4 men, 5 women 7 subjects had normal hearing at octave frequencies Hz; 2 had mild hearing loss at 1 frequency Statistical analysis did not identify those 2 subjects as outliers and were thus kept in the experimental group

7 Materials & Methods Instrumentation - ipod MP3 player was an Apple ipod Video Experimental song chosen was Dave Matthews Band - Ants Marching. Song was chosen based upon college student preference, broad relatively flat frequency response, and generally common intensity level across the song. The song was taken as.wav (Windows PCM format) from the original album and loaded onto the Apple ipod. A 10 second speech spectrum noise that was normalized to the RMS average of the song was appended to the end of the track

8 Materials & Methods Instrumentation - ipod The two transducer coupling conditions were direct earbud in the ear and earbud with earbud Enhancer coupling (ebe)

9 Materials & Methods MATLAB Noise Audiometer Probe Mic Instrumentation - Recording Ear Canal earbud Instrumentation - Noise Presentation Recording In the ear canal recording was completed by a probe microphone used from a Frye 7000 hearing aid analyzer into MATLAB. The noise environment was presented to the subject via two calibrated speakers behind the subject at 45 degree angles in a sound booth.

10 Materials & Methods

11 Materials & Methods Instrumentation - Noise Environment 4 Environmental noise conditions were used for testing Street Noise, Recreational Center Noise, a Perfect Masker, and Quiet Noise at 4 intensities - 60, 70, & 80 dbspl -60dB -84dB -120dB 1k Hz 4k Hz 7k Hz Green - Recreational Center; Red - Street Noise; Purple - Perfect Masker

12 Procedures Each participant completed the following prior to testing: Filled out an informational survey regarding their use of a digital audio player and their preference on use of their earbuds Hearing was screened at octave frequencies from Hz. Otoscopy with cerumen management completed when necessary

13 IHAFF Scale 1- Very Soft 2 -Soft 3 - Soft but Comfortable 4 - Comfortable 5 - Loud but Comfortable 6 - Loud 7 - Uncomfortably Loud Procedures In the booth The experimental setup as seen previously was placed on the participant. The participants were asked to Press play on the ipod when the background noise begins. For the first 60 seconds a song will play and we ask that you adjust the volume of the song to your most comfortable listening level. *show IHAFF scale* We ask that you make your volume level a 4, neither too loud or too soft. Once you have found your most comfortable level, please leave it at that setting. Following the song, there will be a 2 second pause and then 10 seconds of a noise. Please only adjust the volume while hearing the song. This was completed for each randomized presentation of each noise condition and level.

14 Data Analysis An ANOVA analysis was completed to analyze the data based upon the research questions listed earlier The independent variables of this study were: Earbud coupling - Earbud only or ebe Noise - Quiet, street noise, rec center noise, or a perfect masker Presentation level of the environmental noise - 60dBSPL, 70 db SPL, or 80dB SPL The dependent variable was the RMS average sound pressure level in the ear canal at a comfortable listening level Pairwise comparisons were also completed in search of interactions between variables

15 Results Peak Listening Level db SPL (in Street Noise) Min Listening Level db SPL (in Quiet) Mean listening level (across all noise conditions) In quiet - earbud db SPL; ebe 67.2dB 60dB Environmental Noise - earbud 73.60dB SPL; ebe 68.91dB 70dB Environmental Noise - earbud 77.32dB SPL; ebe 73.11dB 80dB Environmental Noise - earbud 81.98dB SPL; ebe 78.34dB SPL ANOVA results Noise level and earbud coupling had a significant effect in all subjects on the comfortable listening level of the digital audio player Type of noise did not create a significant difference in listening level within each condition.

16 Results Although there was no significant difference, mean data supports that the listening level increased from recreational center noise<street noise<perfect masker. There was no significant interaction effects between any of the pairings tested. There was a 4.18 db SPL difference between the comfortable listening level while using the earbud vs. the earbud enhancer. The subjects all listened to the music quieter when using the ebe coupling. There was a 4.45 db SPL average difference in comfortable listening level between the different noise presentation levels. 4.19dBSPL between listening levels with Earbud 4.72dBSPL between listening levels with ebe

17 Sound Isolation The ebe has the greatest amount of sound isolation at approximately 9dB SPL across all presentation levels in comparison to the ear canal alone The earbud alone has approximately 5dB SPL of sound isolation across the frequencies tested. The ebe has approximately 4dB greater sound isolation paired with the earbud than with the earbud alone single subject data Earcanal Earbud ebe

18 Conclusions From the data presented in this study, there is little risk of hearing loss in environments that do not exceed the levels tested in this experiment. On average the users listened to their ipod or digital audio player 1.33 hours per day and 6.33 hours per week OSHA ACGIH dba 95 Max Output 86.69dBSPL Time - hours

19 Conclusions Real world sound measurements of the environments: Recreational center: dbspl (75-80dBSPL avg) Street Noise: dbspl (75-82dBSPL avg) Earbud ebe Street Listening Level dbspl Recreational Center 65 Quiet Noise Presentation Level - dbspl

20 Conclusions The Earbud Enhancers have the tendency to lower the average listening level in comparison to earbuds alone by just over 4dBSPL Direct measurements of sound isolation show that there is approximately 9dBSPL of sound isolation from using the ebes over and open ear canal and the earbuds offer approximately 5dBSPL of sound Listening Level dbspl Earbud ebe 65 Quiet Noise Presentation Level - dbspl

21 Areas of Future Research Collection of more data points Preference data to be explored Intermediate environmental noise intensity levels tested for trend analysis

22 Special Thanks to: Dr. Novak and Dr. Heinz for help with conception of the idea and protocol Dr. Robert Olivera from Hearing Components for the Earbud enhancers and guidance Skyler Jennings for help with MATLAB and statistical analysis