Guest Article: Can Noise Impulses From Softball Hitting Negatively Affect Your Hearing?

Can Noise Impulses From Softball Hitting Negatively Affect Your Hearing?

Editor’s Note: From time to time The Hearing Blog presents interesting guest articles for our Readers. Today’s post is the eighth in our Guest Article series, written by Roseangela Moura, AuD of Houston.

Hearing damage can occur from a variety of ways in the realm of sports activities. From the blasts of instruments to the roar of the crowd, it would seem that one takes their hearing health in their hands at many events. One of the newest concerns that have arisen as a result of this discussion about hearing damage is whether the sound of a softball being hit can afflict hearing damage though impulse noises. Using data gathered through studies of various bat materials hitting softballs compared with known hearing damage thresholds, the evidence is compelling in its suggestion that long-term hearing damage does not occur via softballs being hit by any type of bat.

The study used a setting that is consistent for many softball games: An outdoor playing field that had standard distances between pitcher and batter. This was crucial for the understanding of whether the pitcher or batter was at more risk for potential impulse sounds. All of the softballs used in the original experiment were standard, 12’’ circumference softballs with a 0.40” core, and were presented to the hitter with slow, underhand pitch that would be seen in a softball game. This was important for maintaining the integrity of the collected data (Cook, K., & Samuel, A.).

These measurements of sound presented an opportunity to measure and quantify decibel intensities as well as the pressure level that was exerted through each successful hit. The scale of dB SPL (re 20 µBar) was used to designate the energy present in an impulse wave in each hit. In order to garner an understanding about this designation, Figure 1 compares the dB SPL designations for some common sounds. Understanding the threshold between discomfort and pain is significant because it outlines a model for where hearing loss occurs, which is generally understood as starting at 105dB SPL for at least one five minute duration of exposure (adolescent). This is akin to standing in a loud nightclub, close to the sound source.

Figure 1: Table of loudness of various sounds, and corresponding acoustic pressures Ψa and energy density ε in watts/meter²

Figure 1: Table of loudness of various sounds, and corresponding acoustic pressures Ψa and energy density ε in watts/meter²

In terms of the study that took place, there were three experiments performed to measure the decibel levels that were recorded as well as if the material from which the bat was made would make any difference in the outcome. The three different materials used were aluminum, composite, and then wooden bats, each of which is used in competitive play.

Figure 2: Softball-bat sound measurements in dBC

Figure 2: Softball-bat sound measurements in dBC

The first bat material used was aluminum, which hit a low-velocity pitch that was sent to the hitter underhand. The initial dB rating for this bat was 124.6 dBC, decibels for the specific carrier. The sound pressure at 124.6 dBC was significant, and was presented through the common ringing noise that is heard following a hit by an aluminum bat (Cook, K., & Samuel, A.).

The second bat type, composite material, was faced with the same conditions in terms of location and softball and managed to produce 121.2 dBC, less than the previous aluminum. The sound pressure was not as significant, and elicited a less distinctive sound upon striking the ball.

The third, and final, bat type that was used in this experiment was a wooden bat, which was again subjected to the same conditions and produced a sound impulse that rated 120.0 dBC. Also, the sound produced by this bat had a lower sound when struck than the aluminum or the composite wooden bats. A visual representation of this data is available in Figure 2.

There are many implications that can be drawn from this data. The first is that the sound levels produced by any type of bats hitting softballs are optimized at less than 130 dBC, the threshold for pain in human beings. The information used in conjunction with CDC guidelines for exposure to loud sounds, see Figure 3, suggests that it would take several seconds of consistent levels of impulse sounds at this level to cause hearing damage (decibel). The sounds produced by a bat striking a softball have a duration of less than one second. Therefore, it can be concluded that hearing damage is very unlikely to occur from softballs being struck by any type of bat that is used in traditional softball games.

Figure 3

Figure 3

Figure 4: Sound spectra of wood, composite and aluminum bats striking a softball thrown with an underhanded pitch

Figure 4: Sound spectra of wood, composite and aluminum bats striking a softball thrown with an underhanded pitch

One of the other concerns that were raised through this research is about the specific impulse sound that is produced when a bat strikes a ball. The spectra for the three types of bats were also measured during this study to see the level of Hertz (Hz) produced over time. While each of the bats was able to cover a range of Hz, the aluminum bat produced unusual results during the 0.1 seconds duration of the bat striking the ball. This appeared as two distinct peaks of energy around 1700 Hz and 2260 Hz, which is thought to be the result of the higher amplitude-frequency response of the metallic “ring” that is heard when the bat strikes the ball (Cook, K., & Atcherson, Sam). This data, outlined in spectral analysis on Figure 4, served to corroborate the conclusion that even though aluminum bats could produce higher impulse sounds, short exposures posed no serious threat to the hearing of the players.

 

References:

  1. Adolescent And School Health. (2013, February 27). Retrieved September 29, 2014
  2. Cook, K., & Atcherson, Sam (2014, March 20). Impulse Noise: Can Hitting a Softball Harm Your Hearing? Scientific World Journal. Vol. 2014, Article ID 702723, 4 pages, 2014. doi:10.1155/2014/702723
  3. Decibel Level: Loudness Comparison Chart. (2007, January 14). Retrieved September 27, 2014

 

About the author:

Roseangela Moura AuD, Premier Audiology and Hearing Aid Center, Houston, Texas

Roseangela Moura AuD

Roseangela Moura, AuD has 30 years of experience as an audiologist. She has been with Premier Audiology and Hearing Aid Center since 1999 and currently directs thr audiology department and hearing aid practice. Rose has a Bachelor of Arts degree in Communication Disorders from Texas Tech University in Lubbock, a Master of Science in Audiology from the University of Texas at Dallas, and a Doctor of Audiology degree from Salus University in Elkins Park, PA.

Dr Moura is certified by the American Speech-Language-Hearing Association (ASHA) and is a Fellow of the American Academy of Audiology (FAAA). She is fluent in Portuguese and has a working knowledge of Spanish and French.

 

Bootnote:

Astute readers of The Hearing Blog will notice this switch from db SPL (re 20 µBar) and dBC, with the C-weighting scale corresponding to filtering matching the equal loudness contour of sound at 90dB SPL presented to the human ear.

A, B, and C-weighting transfer function curves

A, B, and C-weighting transfer function curves

Most sound meters are calibrated to display A (dBA) and C (dBC) weighting; but only expensive sound analyzers display true dB SPL. For the purposes of this article, convolving the acoustic pressures Ψa spectra in figure 4 with the C-weight filtering curve yields results that are close enough for this analysis. Our friends at Engineering Toolbox have a more detailed explanation of sound pressure weighting here~

 

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About the author

Dan Schwartz

Electrical Engineer, via Georgia Tech

4 Comments

  1. Samuel Atcherson
    October 3, 2014 at 8:03 am

    Thank you for mention and summary of my former student’s capstone project. I’m not sure, however, why the reference is Cook & Samuel, when it is, in fact, Cook & Atcherson.


    • Dan Schwartz
      October 3, 2014 at 9:52 am

      Sam, thank you for bringing this to our attention. I didn’t write this article, but it has been corrected. Do you have a link to the article?


  2. Paradise Hearing
    February 16, 2015 at 1:57 pm

    Interesting article. Though this research indicates that no serious damage could occur from the sound, it leads an interesting train of thought that should be applied to other sports. Protecting our hearing is important, especially for our youth!


  3. Allison
    March 1, 2015 at 11:18 am

    Thanks for posting. If think you’re suffering from hearing loss, it’s important to get an accurate test so you can take the necessary steps.


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