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Auditory transduction, ear anatomy, and SPL
External, or outer, ear:
Auricle (pinna): “collects sound waves and channels them into the ear canal” (Johns Hopkins Medicine, n.d.).
External auditory canal: responsible for amplifying and channelling the sound towards the tympanic membrane (Johns Hopkins Medicine, n.d.).
Tympanic membrane: vibrates due to the sound that has been channelled to it. This vibration is not actually what we hear, although we often simplify the explanation as such: it will simply repercuss on the auditory ossicles.
Middle ear:
Auditory ossicles: malleus (hammer), incus (anvil), and stapes (stirrup) vibrate (in that order) following the tympanic membrane.
Oval window: this membrane, behind which sits the fluid-filled inner ear, is made to vibrate due to the “piston-like action” of the stapes (Scientific American, 2008).
Inner ear:
Bony labyrinth: Grouping of the vestibule, cochlea, and the semicircular canals (the latter being a collection of liquid-filled tubes dedicated to the sense of balance) (Davies, 2020)(The Nemours Foundation, n.d.).
Vestibule: The vestibule is responsible for balancing our bodies: “the vestibular system is the sensory apparatus of the inner ear that helps the body maintain its postural equilibrium” (Best For Neet, 2017)(Hawkins, n.d.)
Cochlea: Three liquid-filled channels are housed in the cochlea's cone-shaped structure. Movement is detected by an organ called Corti, which is placed between two of the canals, as sound travels through the ducts and the liquid therein vibrates. The minute hairs in the Corti are sensitive to the movement of fluid within the ducts, causing electric signals to be delivered through the nerves and then to the brain. This is the final stage of auditory transduction, in which the brain detects these pulses and translates the sound.
The cochlea, and its organ named Corti, is involved in the human hearing loss process. The cochlea is divided into sections that are responsible for hearing different frequencie. The part closest to the oval window and the middle ear is responsible for hearing high frequencies, while the part closer to the oval window and the middle ear is responsible for hearing low frequencies. Lower-frequency perception is controlled by the "upper" part of the cochlea, which is shown as being closer to the center of the spiral.
The hairs from the Corti organ can be located all around the organ and so follow the complete cochlear spiral. Hearing loss is defined as the inability to hear, or the difficulty in hearing certain frequencies, as a result of damage to a specific set of hairs in various sections of the Corti organ, and thus corresponding to the hearing of different frequencies.
The cochlea is depicted on the left hand side, with the various frequencies that make up the average human hearing range placed roughly around the regions of the cochlea that are responsible for their hearing.
Stereocilia, are hair-like cells that are present throughout the body and within the ear. The image inserted above indicates the way in which dead or injured stereocilia look like, whereby hearing loss is prevalent as a result of this. Hearing loss can occur when safe sound levels are exceded makinging for the human ear. Auditory loss does not occur randomly; it usually occurs in relation to specific frequency or set of frequencies.
Tinnitus can be caused by transient hearing loss in some situations, according to an interaction in class with our facilitator: this is due to the fact that sometimes receptor cells are not entirely dead, but simply damaged, resulting in tinnitus. Their attempt to rise up may have created a resonance within the ear, which we perceive as an unique ringing noise.
Safe exposure to sound
The concept of a "sound dose" can be used to describe sound exposure in terms of hearing impairment and safe exposure levels. Fundamentally, this means that the human ear can only tolerate a specific "amount" of sound per day, which varies depending on amplitude (decibel levels) and time.
In the diagram above we can see different amplitudes, as well as the amount of time we may safely be exposed to sound at particular levels. In terms of the idea of "sound dosage," we're frequently advised that noises louder than 85dB might be detrimental. However, this isn't quite true: one may safely expose oneself to sounds over 100 decibels. However, if someone were to listen to a sound at 115dB for 30 seconds, they would have effectively "consumed" or experienced 100% of their daily permitted exposure to sound, or sound dosage, at any level.
In order to avoid harm, one would have to spend the following 23 hours, 59 minutes, and 30 seconds in total stillness (Kardous et al., 2016). In essence, sounds are not intrinsically dangerous; but, prolonged exposure to specific sound levels might result in hearing loss. With the exception of a recording when Marc clapped to test the acoustic qualities of the space we were in, the noises recorded for this project are much below what might be deemed dangerous. Even back then, the clapping generated peaks in the sound's amplitude, indicating that the sound was emitted in brief bursts of high amplitude rather than in longer or even continuous bursts of sound.
First recording: EMP Studio
Because the studio has been acoustically treated, there is little reverberation: it is an absorptive space.
The EMP clap test, like the rest of the recordings, had a few issues: we hadn't yet figured out what the difference between slow and rapid response times was at the time of the initial recording. Furthermore, we only had a basic comprehension of the difference between frequency weightings A and C, if not a distorted one. As a result, for both the silent recording and the clap test, we used a quick response time with frequency weighting A. Later, when we were about to take a photo of the studio, we realised that we should also record the clap test utilising frequency weighting C and the rapid response time that we had been using, in order to interpret the clapping on the measurements as precisely as possible. The objective of the clap test was largely to evaluate the reverberation inside an acoustically treated space, so this wasn't exactly a priority, but we figured we may as well be as precise as possible in our work.
Because we were capturing a burst of sound, a transient, we needed frequency weighting C and a quick response time for the clap test. The A weighting is great for capturing background noise or generating a broad measurement in relation to acceptable exposure levels, but the C weighting looked like a better, more reasonable alternative for something like a clap, especially in the context of testing. The quick reaction time is only to ensure that the microphone and software do not ignore the sudden/transient sound, as they could if we used a slower response time.
In terms of safe exposure, the records reveal that the EMP studio poses no harm to one's hearing when it is not in use: one could stay in the studio for the whole day without risking their hearing. The clap test is useless here, but if we wanted to talk about it, we might say that claps are brief bursts of sound; the measurements surpassed 100dB, reaching 105.8dB, but it would be impossible to clap enough times to achieve 15 minutes of exposure to 100dB. Given that safe exposure at 103dB is restricted to 7.5 minutes, and at 106dB is limited to little less than 4 minutes (3.75 minutes precisely). Even so, it is quite doubtful that this will occur. And, in the end, the risk must be controlled by the people who use the studio: they get to adjust the monitors to whatever volume they want and applaud as loudly as they want: "amplitude is objective, but loudness is subjective."
In retrospect, it would have been fascinating to analyze both sound pressure levels and reverberation within the studio by playing a sound or possibly music on the monitors. Using clapping instead provided us with the opportunity to learn about and think on what settings are ideal for different types of sounds.
Second recording: Knowledge Park food court
The recording was originally done with frequency weighting C and a quick response time. However, because we were primarily interested in recording background noise or the aggregation of everyone's voices in the food court, we decided that frequency weighting A with a slow response time would be preferable: a fast response time and C weighting, on the other hand, would be ideal for recording bursts of sounds or impulse. However, A would be better to record continuous background noise, and the slow response time, this would be better for recording continuous background noise, and any transient or burst would not affect the measurements: a chair being dragged for a short distance, someone clapping (which actually happened during the "optimal" recording), a short scream or shout would theoretically not be picked up because of the slow response time.
In terms of sound levels, if we take the average of 73.3dB and assume that it remains constant throughout the day (which, to be honest, is probably an incorrect assumption), we are still within the acceptable exposure thresholds. All of the scales we identified seemed to start at 85dB, which is usually regarded as the lower limit, or commencement, of dangerous sound levels. However, because 73.3dB has a lower amplitude than 85dB and is calculated on a logarithmic scale, it is possible to expose oneself to such sound for considerably longer than 8 hours without harming one's hearing.
To address the nature of the recording site, the food court provides us with a huge, open, square-shaped indoor area and no soundproofing, even passively. In that manner, sound may readily echo throughout, and this effect is particularly noticeable in the early afternoon when the crowds are at their greatest, indicating that this is a more reflecting place.
Third recording: Marc's room
Shelter, a song by Porter Robinson and Madeon in conjunction with A-1 Pictures and Crunchyroll, is placed to the side since it is the song I used to collect measurements for listening to music at a comfortable level with a speaker in the room. However, I did not embed the recording because the quality sounded rather low. Furthermore, I strongly encourage everyone who hasn't already done so to view the video, since it is widely regarded as a masterpiece in the "anime" community.
Three takes were required to obtain a quiet environment measurement for this set of recordings (by now, we've clearly established that obtaining a single, unique recording was impossible): on the first attempt, my index finger cracked, which was picked up by my smartphone's microphone and resulted in an amplitude peak. The second attempt at a fully quiet recording was cut short by a clicking sound caused by the room's A/C shutting off automatically.
The third option is a completely quiet recording. There is one essential difference: all recordings were done using the A frequency response, which is the most appropriate in that situation: it matches human hearing in a quiet atmosphere. However, the reaction time was set to fast on the first two recordings, but I learned from my mistakes and changed it to slow for the final recording. There are also two more recordings, Shelter 1 and 2, where I chose to record music on a speaker at a level I considered comfortable and collect measurements from the two areas around the room where I would normally be when listening to music on a speaker.
Due to a variety of factors and conditions, my room is normally kept as quiet as possible. Since a result, there is no risk of detrimental exposure, as such sound levels can be subjected to for a whole day with no risk. When it comes to speaker recordings, I only utilize them on a few instances. When I do this, I keep the music at the same or lower volume. We can observe that there is no substantial danger of injury at that level as well: we average 68.4 and 63.9dB, with maxima at 75.8 and 68.3dB, respectively. It is safe to listen to music from the speaker at the same volume level for more than 8 hours. In my particular instance, I may only utilize the speaker for an hour or two. As a result, we are still well below permissible exposure limits.
Because of the nature of my room, which is rather square and fairly small, as well as the carpeting and bedding, as well as the curtains that cover a good portion of the walls and then the pieces of fabric that cover the curtains and part of the walls themselves, it is fairly well soundproofed, albeit passively. There is some reverb, although it is quite subtle and only present for bigger sounds. As a result, it would be an excellent recording spot. Opening the closets, which are stuffed with garments, emphasises the location's absorptive character even more.
Fourth recording: gym (barbell)
This recording was done fairly haphazardly. We can hear a weighted barbell repeatedly striking the floor.
In the photo, just about half of the gym is visible. It is vital to emphasize the gym's size, which spans a whole warehouse/hangar, if not two. The walls are built of concrete on the bottom half and metal on the upper half, with no covering that may potentially provide absorption. Essentially, there is a lot of sound reflection going on: as one would expect from a vast hangar, there is some reverb. In terms of its potential as a recording place, depending on what one is aiming to capture, and with correct tuning and a suitable setup, this gym, in particular, may make for a fascinating recording site, especially if we were to attempt to capitalise on the reverb.
The recording was configured to utilize the C weighting with a rapid reaction time because we wanted to capture the "banging" of the weights in the barbell area in the far corner of the gym (seen in the image above), which is a transitory sound. There were few people practicing at that time because it was early on a Saturday morning, which was disappointing because it would have been interesting to observe whether there were any noticeable impacts on the amplitude owing to potential constructive interference. At one point, we hear another patron's weights smashing against Marc's, which would have made for a fascinating case study if everything had been synchronized.
In terms of sound levels and exposure, the gym may appear to be more dangerous than one may imagine. This form of thumping is, in fact, rather frequent. Furthermore, the hammering recorded is rather mild in compared to what other people do when they fully drop their barbells or "send them to hell" (purposely slam them into the ground after their repetitions). The phone was positioned to record at roughly the same distance as one's head would be at the end of an eccentric deadlift. Nonetheless, despite the relative softness, we reached peaks of approximately 108dB, with an average of 83dB.
The average is, of course, far from the peak because there were clear periods of stillness between the hammering and all other recorded noises were far lower in volume (for example, a discussion at the end of the recording, which has been cut out of the embedded audio but was still taken into account by Decibel X during the initial recording and measurement). The gym can be considered relatively dangerous because pounding is widespread and rather loud, and one may be exposed to a higher sound dosage than they would expect. According to safety rules, the maximum exposure period at 100dB is 15 minutes.
As previously stated, at 106dB, this is reduced to less than four minutes, and at 109dB, it is reduced to little less than two minutes (1.875 minutes to be precise). As a result, unlike the clap test, this appears to be a far more real and credible instance of hazardous sound exposure than 15 minutes of continuous clapping at 100dB. However, as previously noted, pounding is a transitory sound, which means it has an incredibly quick assault but also a very brief decay, duration, and release. Essentially, it is a sound that lasts a fraction of a second, and the fact that it is tied to a physical repetition means that one can only slam their weights so many times before physical tiredness sets in. As a result, the risk to one's hearing may look significantly more serious than it is. The conclusion is that you should not forego exercise, particularly barbells, merely because you are afraid of hearing damage and loss: there are more tangible health advantages to be achieved than prospective losses.
Comparative Conclusions
The resemblance between the various recordings is one concern that instantly arises with our endeavor. Indeed, because most recordings were made in silence, comparing and contrasting them would be pointless. However, we've tried to provide some diversity by playing music throughout one of the recordings.
We can tell that Marc's room was quieter than the EMP studio when we compare the EMP and bedroom recordings. This is most likely owing to the fact that we heard some movement in the EMP recording, which caused the average sound level to rise. With this in mind, comparing the EMP studio to other environments becomes a little more challenging. The click from the A/C is undoubtedly an issue to consider, but it was the quietest recording of the bedroom, even quieter than the completely silent one.
That discovery is particularly intriguing because we have yet to discover what may have generated such a disparity. At least during the "actual silence" recording, there was no visible peak in loudness, but there was one in amplitude. However, the peak isn't the only odd data; the failed A/C recording's minimum and average were both lower than the purportedly quiet recording, raising issues with no apparent answers.
To compare the food court with the recording during which Shelter (Robinson, 2016) was playing, we may look at the noisier settings. According to NIOSH criteria, none of these records have reached dangerous levels.
At 79.7 decibels, the highest peak was recorded in the Knowledge Park food court. With a measurement of 75.8dB, the initial recording of Shelter (Robinson, 2016) is nearly 4dB lower in this regard. However, there is an 8.2dB difference in the minimum: the lowest measured value in the food court is 68.9dB, which is quite a deal higher than the first music recording's minimum of 60.7dB.
The minimal difference between the second and first recordings of Shelter (Robinson, 2016) is only 1.2dB. The peak, however, is a long way from both the first recording of the song and the peak in the food court: there's a 7dB difference between the first recording and this recording, and a 11.4dB gap between the food court and this recording. The difference in averages is significant, with a difference of 4.5dB between Shelter 1 and Shelter 2.
However, there is a 9.6dB disparity between Shelter 2's average and the food court recording once again. It was amusing to watch this because the first idea was that the music would be louder: it was effectively set by Marc to be at what would seem like a comfortable level, but the food court was merely background noise, therefore it was not considered to be particularly loud. The outcome was unexpected, whether it was related to perceived loudness and the equal-loudness contour or simply because we prefer to "tune out" background noise.
The problem with comparing the gym to the other noisy venues was that we were seeking for a measurement of ambient noises, background noise, and other similar things, but the gym recording was especially focused towards the transient created by the weights. Although the implications and conclusion are rather clear, it may still be fascinating to look at the statistics.
The shift in dynamic range is one of the first things we expected: the gym recording would go from a relatively low 64.1dB to a peak created by the weights, reaching heights of 107.6dB. The difference is then 43.5dB, compared to Shelter 1's now meager 15.1dB dynamic range and the food court's meager 10.8dB. Both of these are sufficient to generate a significant change in loudness, but 43.5dB is enormous. The difference in dynamic range pushes the gym recording's average to 83dB, which may seem surprising given how quiet it is on Saturday mornings.
When the weights are removed, the values are likely to be far lower than on the other two recordings, which makes the increased amplitude pretty humorous. Another amusing aspect is that, despite the peaks, the release and subsequent silence between each transient at the gym was enough to keep the average low enough to avoid being classified as harmful by NIOSH standards, implying that, despite everything, we were unable to obtain any measurement that would indicate harmful exposure in a specific location. If you want to see it, though, you may look at my earlier project, notably the Japanese restaurant KY.
Finally, while this is not a comparable conclusion, we would like to explain more explicitly why we employed different frequency weightings, namely weightings A and C.
We can read and see a graphic depiction of the differences between the A and C frequency weightings in the accompanying screenshot, which was acquired from NoiseMeters' website.
Both are intended to mimic the human ear's reaction to sound. Our hearing, on the other hand, responds differently to different sound intensities and frequencies. The goal of having these two independent weightings (along with a few others) is to be able to describe and quantify sound levels as precisely as possible, much like the human ear.
By default, my group used frequency weighting A, which isn't always a bad thing: in most circumstances, contexts, and applications, this weighting approximates human hearing. However, at the start of week 7 we concluded that frequency weighting C was better for loud noises, peak level measurements, and transient and pulse measures. When clapping hands or pounding weights at the gym, for example, the noises are not just transients, but they also approach or exceed 100dB.
When it comes to clapping, this might vary: it can occasionally be somewhat lower than 100dB, more in the 90dB area. Weights, on the other hand, typically, if not always, reach 100dB or more, if not much more, depending on who is using/slamming them. As a result, in these two specific circumstances, and particularly in the gym recording, utilizing weighting C is particularly important. Not only that, but both of these noises - clapping and weights pounding - were recorded at their highest volume levels. And because we were seeking to quantify precisely that, it was only natural to employ weighting C.
Weighting A, on the other hand, made sense for the other measures because we weren't trying to quantify any impulsive, transient, or peak sound levels, but rather the overall sound level at a specific place.
PROJECT REFLECTION
The major goal of this second study was to understand and assess how sound is measured and how various weightings are employed in different contexts. We were needed to utilise exploration and learning approaches to effectively describe and evaluate our findings while reporting the output reading of each acquired sound utilising a decibel measuring device to reach and satisfy the project's aims. I appreciated working on this group project with Marc since we were able to gain a lot from one other's existing expertise. Despite not being completely within lessons at the start of this project, I was able to thoroughly comprehend the project objective and rapidly come up with a recoding and evaluation through Marc's advice. It was an amazing pleasure to be able to discuss each of our discoveries.
I feel that having the chance to not only learn how to accurately define our track audio levels but also perform in-depth study on the elements of the ear and how they work together to hear sound was an incredible learning curve. At the start of my analytical process, I found it difficult to comprehend the work at hand, but with more study, I was able to successfully use my knowledge to describe, compare, and contrast my recording results.
Following input from my peers and instructor, my next steps will be to identify what may be done better for future project submissions and to incorporate the suggestions obtained. However, I believe that I could improve my communication skills with my partner, since I believe that we were sometimes unaware of how the process and project we’re developing. In the future, I hope to perform more detailed study on each of the several connected subtasks to be able to coherently explain and comprehend how different components of the audio world and track analysis interact with one another. This will allow me to do a more in-depth examination and will aid me in drafting up my comparative section.
Overall, I believe that the most well-reflected transferrable abilities taught and implemented during this project have been critical thinking, problem solving, and time management. I feel skills were represented in this assignment since I was forced to conduct cohesive study on all of the numerous features that comprise this project's analysing process. In terms of time management, I believe that this transferrable ability was shown in my project through the limited periods that we were given to finish the project owing to other continuing units. Overall, I had a fantastic learning experience and am looking forward to the next assignment.
REFERENCES
24 Fitness. (n.d.). Facility - 24 Fitness Gym in Al Quoz Dubai. 24FITNESS. Retrieved March 26, 2022, from https://www.24fitnessdubai.com/our-facilityBest For Neet. (2017, August 7). CBSE Class 11 Biology || The Ear [Video]. YouTube. https://youtu.be/m2AzmoVCB6IDavies, K. (2020, December 14). The Inner Ear - Bony Labyrinth - Membranous Labryinth. TeachMeAnatomy. Retrieved March 21, 2022, from https://teachmeanatomy.info/head/organs/ear/inner-ear/Decibel X (8.0.1). (2022). [Mobile application]. SkyPaw Co., Ltd.https://play.google.com/store/apps/details?id=com.skypaw.decibel&hl=en&gl=USHawkins, J. E. (n.d.). human ear - The physiology of balance: vestibular function. Encyclopedia Britannica. Retrieved March 21, 2022, from https://www.britannica.com/science/ear/The-physiology-of-balance-vestibular-functionJohns Hopkins Medicine. (n.d.). How the Ear Works. Johns Hopkins Medicine. Retrieved March 21, 2022, from https://www.hopkinsmedicine.org/health/conditions-and-diseases/how-the-ear-worksKardous, C., Themann, C. L., Morata, T. C., & Lotz, G. (2016, February 8).Understanding Noise Exposure Limits: Occupational vs. General Environmental Noise | Blogs | CDC. CDC Blogs. Retrieved March 21, 2022, from https://blogs.cdc.gov/niosh-science-blog/2016/02/08/noise/NoiseMeters Inc. (n.d.). Frequency Weightings - A-Weighted, C-Weighted or Z-Weighted. NoiseMeters. Retrieved March 28, 2022, from https://www.noisemeters.com/help/faq/frequency-weighting/Robinson, P. [Porter Robinson]. (2016, October 18). Porter Robinson & Madeon - Shelter (Official Video) (Short Film with A-1 Pictures & Crunchyroll) [Video]. YouTube. https://www.youtube.com/watch?v=fzQ6gRAEoy0&feature=youtu.beScientific American. (2008, January 31). How do the hammer, anvil and stirrup bones amplify sound into the inner ear?Scientific American. Retrieved March 21, 2022, from https://www.scientificamerican.com/article/experts-how-do-the-hammer-anvil-a/The Nemours Foundation. (n.d.). Word! Semicircular Canals (for Kids) - Nemours KidsHealth. Kids Health. Retrieved March 21, 2022, from https://kidshealth.org/en/kids/word-semicircular-canals.html
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