Schlauch Laboratory

Applied and Basic Research: Educating the next generation of Audiologists and Researchers

My name is Bert Schlauch and I am a Professor in the Department of Speech-Language-Hearing Sciences at the University of Minnesota (Twin Cities). My lab addresses a broad range of questions in basic and applied hearing research, but one underlying principle permeates everything I do: I involve students in my research. Many former students - undergraduate and graduate - have published scientific papers with me. Here is a link to those studies. My former students are currently employed in diverse positions as clinical audiologists, researchers in industry, and university faculty. 

 Consider applying for our graduate programs.  Interested in an academic career or in a job that involves clinical research?  We currently have funding available for qualified applicants to our Ph.D. program (next round, December, 2019).  The Center for Applied and Translational Sensory Science also has fellowships to study hearing.  Contact me to learn more ([email protected])

 

Research Projects

 

Below is a summary of some current projects we are working on.  Follow the links to learn more and to listen to some sample sounds.

Improving the precision of audiological behavioral measures:  My students' and my work in this area has improved diagnostic tests for identifying persons with tumors and ones faking a hearing loss.  My current work is refining pure tone threshold measures used to identify persons showing damage from exposure to intense sounds. A publication in the American Journal of Audiology(with Edward Carney) presents evidence that several highly cited published studies significantly overestimate the percentage of teens who have damaged hearing from listening to loud sounds. The story was picked up by Minnesota Public Radio.

Heekyung Han, a research audiologist, enrolled in the Ph.D. program in Fall, 2013,Dr. Aparna Rao and I presented the results of a study at the American Auditory Society in March 2014 that is now published in the American Journal of Audiology.  We measured the accuracy of non-native English speakers and hearing impaired audiologists to administer and score speech tests with and without visual information.  Visual cues helped both groups but the difference for the hearing impaired audiologists was substantial.  For persons who are unable to achieve the desired accuracy, even with visual cues, we present alternative solutions. We also have a paper that will be published later this year that compares 4 choice word recognition to an open-set condition (where the person repeats what they heard with no choices in front of them).  The study found that it requires more than 1200 presentations of the 4-choice condition to equal the precision of the open-set condition.  This has implications for pediatric patients, some persons with aphasia,  and for conditions where the patient is unable to respond clearly with a vocal response. 

We are beginning a project to teach monolingual English speaking audiologists to score Spanish word lists administered during a hearing test.  Audiologists and audiology students will learn and receive feedback using audio-video recordings that are designed for this purpose.  It is important that audiologists consider that the USA is a multicultural and multilingual country and that hearing services need to address issues in culture and language. We are basing this program on the successful results of an active training program for Korean that was completed in my laboratory.

One challenge that arises is how to quantify the level of speech for audiological testing and for creating standardized tests.  I worked on a project with Emily Chu, a junior at Wayzata High School as part of the Honors Mentor Connection Program. The results (Download 2019 Chu AAS Poster 5.0) were presented at the 2019 annual meeting of the American Auditory Society.

Auditory Attention: We seldom listen to sounds in isolation.  The brain does a wonderful job of segregating sounds that we attend to from other, competing sounds.  This work explores the acoustic cues that the brain uses to accomplish this segregation (Click here for more details).

Sounds played backwards: It's an urban legend that if you play one of the Beatles's songs backwards it will reveal a lyric that Paul is dead. Ignoring that hoax, everyone knows that speech or music played backwards has a very different timbre or tone color than sounds played in the normal way.  I quantified some of these effects and discovered that the duration of a common class of sounds played backwards is perceived to be twice as long as the same sound played in the normal fashion.  This finding has implications for composers and for the study of timbre (Listen to the sounds here).

Speech Prosody: Prosody is the feature of speech that describes its melody and rhythm. Most English speakers think of prosody as the feature that enables speakers to convey emotion or, for instance, to signal whether a question is being asked (e.g., a rising pitch at the end of the utterance).  Our studies have found that natural prosody helps listeners understand speech better in background noise (Click Here to Learn More).

Teaching: I routinely offer three different classes. 

Hearing Science (SLHS 3306).  This is an undergraduate class that covers physiological and psychological acoustics.  Click here to read about a project completed by an Honors student enrolled in my class.  She examined the output levels of music CDs to learn if reports we had read about loudness wars were correct and what the consequences may be for risk of hearing loss for persons listening to personal stereo devices, such as IPods. Another undergraduate honors project measured the effectiveness of earglasses (click here to read about earglasses). This course is currently taught by Dr. Evelyn Davies Venn.

Signals and Systems in Audiology (SLHS 8803). This course covers advanced topics in acoustics and calibration of audiometers.  In the image below, some of my students are assessing the calibration of the bone conduction oscillator using an artificial mastoid. 

Behavioral Audiological Assessment (SLHS 5801):This semester-long course covers most of the the diagnostic battery of tests, including pure tone audiometry, masking, speech measures, and immittance.  This course also covers methods of dealing with persons who fake a hearing loss, the topic of funding awarded by the US Navy to my lab.  In the image below, a student is practicing masking technique using a computer simulation.  The simulated patient responds to presentations just like a real client.

 

Hearing Science Foundations of Audiology (SLHS 8805): My background in hearing science and audiology give me a unique perspective that enables me to make critical links between hearing science and audiological clinical practice; hearing science is shown to be an important foundation for evaluating clinical protocols.  As part of this class, students create a poster that presents an analysis of current scientific literature.  The posters illustrate links students find between hearing science and Audiology for a narrow topic in an area of their interest. These posters are presented (even and odd numbered posters presented during alternate, 1/2-hour periods) during the final exam period in a public forum that is attended by other students and faculty.  This group presentation, with multiple posters being presented simultaneously to interested observers, is similar to the format of a national convention (without the stress).  

 

Photography

 
One of my hobbies is photography so when Dr. Mark Bee (professor of Ecology, Evolution and Behavior) asked me to join him with my camera on a field trip to collect frogs for his hearing research, I eagerly agreed.  The fruits of our labor paid off.  Mark's article was the feature article in the journal Hearing Research, and my photo represented his work on the cover of the March 2012 issue.  The photo is shown below. 

 Here is another photo I captured at a parade in Northeast Minneapolis.  This photo was selected for a juried exhibition at the Minnesota Center for Photography as one of 63 contemporary photographs from 36 artists.

 

Below is a photo of eclipse watchers on campus. 

Flattened Fundamental Frequency

A talker's fundamental frequency (the pitch of their voice) varies continuously in typical speech.  Computer programs now enable modifications to the fundamental frequency which give us a tool to study what  role prosody plays in speech understanding.  Sharon Miller worked on this project while she was earning an MA degree with an emphasis in Audiology.  As part of Sharon's thesis, which is published in Journal of the Acoustical Society of America, we examined the ability of listeners to understand key words in sentences in which she had modified the pattern of the voice pitch. The sentences were presented in background noise.  Here are a few examples:

For reference, listen to this normally spoken sentence.

This is an example of monotone or flattened fundamental frequency.

Here is a sentence with variation, but it's unnatural. The fundamental frequency is sinusoidally frequency modulated (FM) with a modulation frequency of 2.5 Hz.

We found that ANYchanges made to the fundamental frequency of a talker's voice made speech understanding in noise worse.  Even though the example with FM modulation sounds more natural (at least to some of us) than the flattened example, speech understanding was poorer in that condition than the flattened one.  That's why we were surprised when we examined the ability of people to understand Tony's speech in noise. Tony, shown below, communicates with an electrolarynx.  In the photo below Tony is using an electrolarynx manufactured by Griffin Laboratories.  His device, unlike most that others that produce monotone speech, has a touch-sensitive button that allows its user to vary the fundamental frequency over time. Tony is shown below with his TruTone electrolarynx.

 

Professor Peter Watson and I recorded Tony producing sentences with his electrolarynx with a varying fundamental frequency and with the same device set to produce a monotone fundamental frequency.  Listeners, under controlled experimental conditions, were able to understand Tony's speech with a varying fundamental frequency better than they were when the fundamental frequency was monotone.

Examples of Tony's speech:

Here is a sample with a monotone fundamental frequency frequency.

Here is a sample with time varying fundamental frequency that Tony produced by pressing the "pitch" button on his device. 

The 12% better speech understanding in noise obtained with the varying fundamental frequency represented a significant improvement. 

A research article describing this work appears in the American Journal of Speech Language Pathology. The goals of this line of work are to understand the role that prosody plays in speech understanding and to improve the quality of speech production for persons with speech disorders. 

Here is an example of a native Korean exaggerating voice pitch in a Sentence.

Here is the same Sentence with a flattened voice pitch. 
. 
. 

Sounds Played Backwards

The amplitude of many sounds in our environment comes on abruptly and decays gradually over time. The sounds produced when an object is struck produce this kind of sound pattern. Some waveform examples are shown below. These waveforms show amplitude on the vertical axis and time along the horizontal one.

The upper panel shows a strike of a snare drum whereas the lower two panels represent the word "time" spoken by a male talker. In the middle  panel, the word "time" is spoken in a small room whereas the lower panel  has echoes present because it was produced in a large auditorium (simulated). In the auditorium, the sound takes longer to decay due to echoes or reverberation.

Listen to the following tones played frontwards and backwards and judge for yourself which one is longer. The tone played frontwards has the same waveform shape (envelope) as the waveforms above. The backwards one is the same sound simply reversed in time. 

Tone played frontwards.

Tone played backwards.

Even though both tones are the same physical duration (1/10th of a second) the second one with its amplitude coming on slowly and decaying quickly sounds longer.  This same finding holds for more complex sounds such as speech and sounds produced by musical instruments. 

The explanation for the finding likely has a cognitive component.  Persons may ignore the decay of a sound because they perceive it as an echo.  My students and I describe the various hypotheses in our scientific papers on this topic (see papers related to ramped and damped sounds or rising intensity and falling intensity sound in my CV).

Some definitions of timbre describe it as the attribute of a sound that enables a listener to judge one sound as dissimilar from another sound using criteria other than pitch, loudness and duration. Timbre is what enables us to recognize different musical instruments when they play the same note. Our findings suggest that studies of timbre should match sounds for their subjective duration rather than their physical duration. 

Auditory Attention

Chris Plack, my friend in England, describes the problem clearly in his book The Sense of Hearing. Below is a figure from his book that illustrates what our ears do on a daily basis.  In the figure below, Chris is shown being presented simultaneously with the sounds of a car engine, a speaker, and speech. The sound waves add to form a single waveform and in order to hear out the sound we want to attend to, the ear has to segregate the relevant sounds from the combined waveform. 

 

To learn what cues the brain uses to perform this task, we are studying listeners' ability to hear loudness differences for a single tone presented in isolation and in the presence of 8 distracter sounds.  Below is an example of the tone presented in isolation.  It will be presented in pairs, and listeners have to judge whether the first or the second tone in the pair is louder.  The difference in the level of the tone is 4 dB; most people can hear a 1 dB difference so the louder tone in the pair should be discriminated easily.

In the following sequence, you will hear 4 pairs of tones.  Judge whether the first tone in the pair or the second tone in the pair is louder.

Four pairs of tones in isolation.

Answers:

1. First Tone

2. Second Tone

3. First Tone

4. Second Tone

Now listen for that same tone again and try to ignore the eight distracter tones. 

 Four pairs of tones in the presence of simultaneously presented distracter tones.  

That was probably harder.  I will have to check the answers after spectral analysis of the stimuli.  I can't trust my ears on this one or the next one. I'm at near chance performance (50%) on this task.  A study participant with absolute pitch was able to hear out the target tone and had a near perfect score after judging hundreds of pairs. 

This time (below) the distracter tones will be presented but the target tone will be turned on with a roughly 1/3-second delay.  All of the tones are terminated at the same time.  Listeners find this task easier. The delay in the onset of the target tone makes it easier to attend to. I perform near 80% on this task.

Four pairs of tones in the presence of distracters with the onset of the target delayed.

We tend to judge sounds that come on together as originating from a single source.  That's likely why it was harder to segregate the single tone from the distracters in the previous condition.  We are also examining other acoustic cues, such as frequency modulation, that might assist in enabling listeners to hear out the single tone from the distracters.   

Hearing Science at the University of Minnesota

There are many hearing scientists at the University of Minnesota in a variety of departments. Several of us meet on a weekly basis throughout the year to discuss our research and to review current literature in the field, mostly from the Journal of the Acoustical Society of America.  Students are invited  to attend these meetings with us. 

Many of us are members of an Interdisciplinary Graduate Group in Auditory Perception and Neuroscience

Below is a list of Bert Schlauch's colleagues who study hearing at the University:

Mark Bee

Arlene Carney

Edward Carney

Heather Kreft

Hubert Lim

Robert Margolis 

Josh McDermott (Alumnus)

 

Christophe Micheyl (former colleague who now works at Starkey)

Ben Munson

David Nelson

Peggy Nelson

Andrew Oxenham

Neal Viemeister

Peter Watson

Magdalena Wojtczak

 

Yang Zhang

Schlauch CV

Download Schlauch CV Dec 2016

Publications with Students

   

  

    My former and current students who have published papers in peer-reviewed journals with me are highlighted in blue below. Some photos of current students are shown below.  Some photos of current students appear below.

  

    Jahner, J.,Schlauch, R.S., & Doyle, T.  (1994).  “A comparison of American Speech-Language-Hearing Association guidelines for comparing speech recognition thresholds,”  Ear and Hearing l5, 324-329.

 

    Schlauch, R.S., & Morison, L.M.  (1995).  “The spectral spread of loudness adaptation for tones that decrease continu­ously in level,” Acustica 8l, 279-280

 

    Schlauch, R.S., Harvey, S. & Lanthier, N. (1995). “Intensity resolution and loudness in broadband noise,” Journal of the Acoustical Society of America 98, 1895-1902.

  

    Schlauch, R.S., Levine, S., Li, Y., & Haines, S. (1995). “Evaluat­ing hearing threshold differences between ears as a screen for acoustic neuroma,” Journal of Speech and Hearing Research 38, 1168-1175.

  

    Schlauch, R.S.,Arnce, K.D., Morison, L.M., Sanchez, S., & Doyle, T.N.   (1996). “Identification of pseudohypacusis using speech recognition thresholds,”Ear and Hearing 17, 229-236. (1,3,4,6)

 

    Mineau, S.,& Schlauch, R.S.  (1997). “Threshold measurement in patients with tinnitus: Pulsed or continuous tones,”  American Journal of Audiology 6, 52-56.

  

    Schlauch, R.S., Lanthier, N., & Neve, J. (1997).  “Forward masked intensity discrimination: Duration and spectral effects,”Journal of the Acoustical Society of America 102, 461-467.

 

    Schlauch, R.S., DiGiovanni, J.J., and Ries, D.T. (1998). “Basilar membrane nonlinearity and loudness,” Journal of the Acoustical Society of  America 103, 2010-2020.

  

    Schlauch, R.S., Clement, B.R., Ries, D.T., and DiGiovanni, J.J.(1999). “Masker laterality and cueing in forward-masked intensity discrimination,” Journal of the Acoustical Society of America 105, 822-828.

  

Ries, D.T., Rickert, M.and Schlauch, R.S. (1999).  “The peaked audiometric configuration in Meniere’s disease: disease related?,” Journal of Speech Language Hearing Research 105, 822-828.

 

Hunter, L.L., Ries, D.T., Schlauch, R.S., Levine, S.C., and Ward, W.D. (1999). “Safety and clinical performance of acoustic  reflex   tests,” Ear and Hearing 20, 506-514.

  

Schlauch, R.S., Ries, D.T. and DiGiovanni, J.J. (2001). “Duration discrimination, and subjective duration for ramped and damped sounds,” J. Acoust. Soc. Am. 109, 2880-2887.

  

 DiGiovanni, J.J.,Nelson, P. and Schlauch, R. (2005). “A psychophysical evaluation of spectral enhancement,” Journal of Speech, Language, Hearing Research 48, 1121-1135.

  

 Opperman, D.A.,Reifman, W., Schlauch, R..S. and Levine, S. (2006). “Incidence of spontaneous hearing threshold shifts during modern concert performances,”  Otololaryngology Head. and Neck Surgery 134, 667-673.

 

DiGiovanni, J.J.and Schlauch, R.S. (2007). “Mechanisms responsible for differences in perceived  duration for rising-intensity and falling-intensity sounds,” Ecological Psychology 19(3), 239-264.

 

Ries, D.T., Schlauch, R.S. and DiGiovanni, J. (2008). The role of temporal  masking patterns in the determination of subjective duration and loudness for  ramped and damped sounds. Journal of the Acoustical Society of  America, 124(6):3772-3783. 

 

Miller, S., Schlauch, R.S., and Watson, P.J. (2010).  The effects of fundamental frequency contour manipulations on speech intelligibility in background noise. Journal of the Acoustical Society of America, 128(1), 435-443.

          Sharon Miller  was featured in a University of Minnesota E-newsletter! 

 

Jin, S., Nelson, P.B., Schlauch, R.S. and Carney E. (2013). Hearing Conservation            Program for Students in Marching Band: Do hearing tests Indicate the Risk for Noise-Induced Hearing Loss?, American Journal of Audiology, 22, 26-39.

 

Schlauch, R.S., Anderson, E.S., and Micheyl, C. (2014). A demonstration of improved precision of word-recognition scores. Journal of Speech Language Hearing Research, 57, 543-555. 

Han, H.J., Schlauch, R.S. and Rao, A. (2014).  The effect of visual cues on the scoring of clinical word-recognition tests. American Journal  of  Audiology. doi:10.1044/2014_AJA-14-0024.

 Schlauch, R.S., Koerner, T. and Marshall, L. (2015).  Effective identification of functional hearing loss using behavioral threshold measures  Journal of Speech Language Hearing Research, 58, 452-465.

Zhang, Y., Cheng, B., Koerner, T. K., Schlauch, R. S.,Tanaka, K., Kawakatsu, M., ... & Imada, T. (2016). Perceptual TemporalAsymmetry Associated with Distinct ON and OFF Responses to Time-Varying Sounds with Rising versus Falling Intensity: A Magnetoencephalography Study. Brain Sciences, 6(3), 27.

Schlauch, R.S., Han, H.J., Yu, T.L. and Carney, E. (2017).  Pure tone-spondee threshold relationships in functional hearing loss: a test of loudness' contribution. Journal of Speech, Language, Hearing Research, 60:136-143. doi:10.1044/2016.

Basu, S., Schlauch, R.S. and Sasisekaran, J. (2018). Backward masking of tones and speech in people who stutter and do not stutter.  Journal of Fluency Disorders, 57, 11-21. 

Yu, T.L. and Schlauch, R.S. (in press). Diagnostic precision of open-set versus closed-set word recognition testing. Journal of Speech Language and Hearing Research.

Below is a photo of Tzu-Ling Yu and me with a poster we presented at the 2016 meeting of the American Auditory Society.  The poster content was published in JSLHR in 2016 with Heekyung Han and Edward Carney. Tzu-Ling and Heekyung are current Ph.D. students in my lab. 

 

 

Below is a poster presented at the American Auditory Society in March 2014 with Ph.D. student Heekyung Han and Dr. Aparna Rao. Heekyung and I are in the photo below.  The study's results are published in the American Journal of Audiology.

Below is a photo of Andrew Kersten, a former AuD advisee, and Tzu-Ling Yu who worked on a project to document the performance of prototype musician earplugs for a company named "Vibes." The earplug that was developed was featured on an episode of Shark Tank.

 

 

One of our most recent projects has a goal of to develop a simple test for unilateral feigned hearing loss.  Sarah Rosen and Tzu-Ling Yu are working with me on this study.

  

The Effectiveness of Earglasses: An Honors Project

Prior to the invention of electrically powered amplifiers, persons with hearing loss relied on mechanical devices to to direct and amplify sound.  This image to the left shows a page from a 1904 Sears Catalog depicting a variety of devices available at that time.

You don't have to shop for antiques on Ebay to find a passive sound amplifier. In the early 21st century, Earglasses, which are similar in concept to the auricles pictured in the Sears Catalog, became available.  I purchased a pair from one of those catalogs that are mailed to every residence within a particular zip code.  The Earglasses are shown here in the original ad.

An honors student in Speech-Language-Hearing Sciences who was enrolled in my Hearing Science course signed up for an honors contract to measure the effectiveness of the Earglasses. 

She worked with a graduate student in Audiology to make measurements using a hearing aid test box.  The hearing aid test box generated a wideband sound that was produced by a speaker. This is how the effectiveness was tested.

1. A  small microphone placed near the eardrum of a subject to measure sound level in one ear.

2. The loudspeaker generating a wideband sound was rotated 360 deg (azimuth) around the subject's head while the sound pressure level was measured.  These measurements were made with and without the Earglasses.

3. The difference in level (in dB) between what was measured with and without the Earglasses represents how sound was changed by the Earglasses.

4. The plots below  show the results for two azimuths. The 0 deg plot (upper figure) was obtained with the speaker about 1 meter from the subject's head and directly in front of him.  A useful device would amplify the sound yet there is very little difference in dB between the two conditions (with and without Earglasses).  The lower plot shows results from 180 deg, directly behind the person.  Sound was reduced a few dB in the high frequencies and not at all in the low frequencies (this is expected because the wavelength at low frequencies is longer and can wrap around the device).  Although this is a favorable oucome, the difference in dB is small. 

We concluded the a wearer of Earglasses would probably not experience meaningful changes in their ability to communicate.

 

 

 

 

 

 

 

 

 

CD Power, Loudness Wars, and Risk of Hearing Loss: An Honors Project

Honors Students in the BA degree program in Speech-Language-Hearing Sciences have an option of signing up for an honors contract while completing a course in their major.  This fulfills an honors degree requirement.  Students electing this option complete the regular requirements for a course as well as an additional project designed for the student by the professor who offers the course. 

 

Here is Marie's project that examined a sample of rock music CD's from 1990 to 2010.  The goals of her project were to: 1) document the trend for RMS (root-mean-square) power of CDs to learn if power increases over time (the year the CD was mastered) in her sample.  This trend has been reported elsewhere and 2)  to infer what the consequences might be for risk of hearing loss for persons who listen to CDs with different RMS levels without changing the volume control (for instance, while jogging).   

 

The text, tables and figures that follow comprise Marie's report that was submitted to fulfill her honors contract for my undergraduate hearing science course. 

 

Methods

 

Using CD recordings of popular rock music ranging from 1990 to 2010, Praat software was used to obtain average RMS power of a sample of the recording. Samples were taken from five different albums for each two-year length of time. In each CD, a released single song was used, and RMS measurements were taken using 60 second samples (from time 1:00 to 2:00).

      

 

Results

Artist	Song	Rel. Year	Avg RMS Power (dB)*
Nirvana	Smells like Teen Spirit	1991	78.46027
Nirvana	Come As You Are	1991	77.87609
Pearl Jam	Alive	1991	80.09812
Pearl Jam	Even Flow	1991	79.77917
Nirvana	Heart Shaped Box	1993	79.99189
Nirvana	All Apologies	1993	79.00152
Alice in Chains	Down in a Hole	1992	81.27465
Alice in Chains	Rooster	1992	74.93313
Alice in Chains	Grind	1995	82.3233
Alice in Chains	Heaven Beside You	1995	80.7176
Pearl Jam	Spin the Black Circle	1994	82.52034
Pearl Jam	Not for You	1994	81.56941
Matchbox 20	Push	1996	81.01531
Matchbox 20	3 AM	1996	80.34982
Creed	What's This Life For?	1997	82.12753
Creed	My Own Prison	1997	81.7389
Eve 6	Inside Out	1998	81.673
Eve 6	Leech	1998	81.26283
Blink-182	What's My Age Again?	1999	81.42304
Blink-182	All the Small Things	1999	84.00382
Godsmack	Awake	2000	83.70529
Godsmack	Greed	2000	84.43933
Creed	Higher	2000	81.97862
Creed	With Arms Wide Open	2000	80.63681
3 Doors Down	When I'm Gone	2002	82.67307
3 Doors Down	Here Without You	2002	81.51279
Red Hot Chili Peppers	By the Way	2002	82.677
Red Hot Chili Peppers	Can't Stop	2002	83.40131
Green Day	American Idiot	2004	85.26495
Green Day	Boulevard of Broken Dreams	2004	84.52495
3 Doors Down	Let Me Go	2005	83.46834
3 Doors Down	Behind Those Eyes	2005	83.43522
Red Hot Chili Peppers	Dani California	2006	84.32203
Red Hot Chili Peppers	Hump de Bump	2006	83.05219
Audioslave	Revelations	2006	84.6185
Audioslave	Original Fire	2006	85.04295
Hurt	Wars	2009	82.28482
Hurt	Pills	2009	83.17376
The Killers	Human	2008	82.96131
The Killers	Spaceman	2008	83.87393

*dB SPL values arbitrary in the table and are only useful for comparison with each other. dB SPL levels were calculated from Pa using the formula 20LOG₁₀(X/2x10^-5). Actual decibel level would depend on the volume setting of the music device.

 

 

A trend toward increasing intensity was found for the forty rock music samples. dB levels of samples from 1990 to 1993 were averaged (78.92 dB) and subtracted from the average of 2005 to 2009 samples (83.83 dB), and a 4.9 dB SPL change overall was found.

 

Discussion of Potential Hearing Risk

 

The National Institute for Occupational Safety and Health (NIOSH) sets a standard for hearing safety in noise in an effort to prevent occupational hearing loss. NIOSH specifies that the maximum permissible level of noise is 85 dB SPL. At 85 dB, workers are allowed a 100% noise dose, which is defined as “noise exposure expressed as a percentage of the allowable daily [work day] exposure.” So, a 100% noise dose at maximum permissible level means hearing 85 dB noise for 8 hours. NIOSH considers this to be the safety cutoff for noise. To determine noise dose for sounds louder or softer than 85 dB, NIOSH uses a 3 dB exchange rate, sometimes referred to as a doubling rate. NIOSH specifies that for every 3 dB increase in intensity, noise dose is considered to double. This means that for every 3 dB increase, safe listening time is halved. An 85 dB noise can be listened to for 8 hours without damaging hearing, but an 88 dB noise can only be listened to for 4 hours. http://www.cdc.gov/niosh/docs/96-110/appA.html

 

What does this mean for music intensity and hearing damage? Zalewski and Baur (2008) measured Preferred Loudness Levels (PLL) of men and women who used portabe mp3 devices. They found that when listening to music devices in noise (similar to the experience of wearing earbuds in an outdoor or public setting) men set their devices at 91.94 dB and women at 84.53 dB SPL. Applying NIOSH standards, men can only safely listen to their music for less than 2 hours, and women safely around 8. If listeners set their PLL for a song released in 1990 during shuffled play, music released later, which may be 4.9 dB louder, can damage their hearing in much less time.