AUD175 Project 2

SPL Measurements

Introduction:

As an audio engineer it's important to understand noise pollution and how it can affect our recordings, safe listening levels to avoid permanent hearing damage along with psychoacoustics' the study of how humans perceive sound. The task for this project is in a group of 2-3 people record and log the dBSPL of different locations and discern whether or not they would make for a good recording location based on the results and the surrounding environment. Along with describe what and how dBSPL is and measured along with details on how humans hear and perceive sound.

Psychoacoustics:

Psychoacoustics is the study of how humans hear and perceive sound. Sound is comprised of high and low pressure waves that move through a medium such as air or water and make contact with our ear drums which we then perceive as sound. "Sound waves follow physical principles that can be applied to the study of all waves" Berg, R. (1998).

"The Fletcher Munson Curve is a graph that illustrates an interesting phenomenon of human hearing." and "As the actual loudness changes, the perceived loudness our brains hear will change at a different rate, depending on the frequency". E-Home Recording Studio (na). The range of Human hearing is on average 20hz to 20,000hz however our perception of the loudness verse's the actual intensity of the sound is very different depending on the frequency. The graph shows how the louder the sound is the more flatter out hearing response to the frequencies are while the more quieter the sound is the more skewed our perception on the sound becomes.

H., J. (2021)

dBSPL - Sound Pressure Level:

dBSPL or Decibel Sound Pressure Level is the pressure level in pascals of a sound source. Every time a sound source doubles in volume the dBSPL will increase by 3 and for every time the sound source is halved the dBSPL will decrease by 3.

The dBSPL Meter's we used for this project was a TENMA Sound Level Meter (2021) and a Decibel Meter iPhone application (2021).

The difference between A and C weighting is an A weighing has a bias against lower frequencies and is meant to simulate human hearing. While C weighting has a more flat frequency response. "The A-frequency-weighting scale is useful in describing how complex noises affect people. Thus, the scale is recognized internationally for measurements relating to prevention of deafness from excessive noise in work environments". Hosch, W. (2006).

Tenma. (2021)

Decibel Meter. (2021)

NTI. Audio. (na)

How Human's Hear Sound:

The human ear is made up many different components which each play a vital part in allowing us to determine the direction and pitch of any given sound.

Outer Ear:

The outer ear also know as Pinna is physical extremity of the ear. "The pinna also performs a crucial function in imprinting directional information on all sounds picked up by the ear." (Everest & Pohlmann. 2009). The shape of the Pinna Reflects incoming sound and prepares it for the inner ear. "It also allows differentiation of sound from all around the listener." (Everest & Pohlmann, 2009).

Auditory Canal:

The Auditory Canal is a tube like structure between the Pinna and the Eardrum. "The primary pipe resonance amplifies the sound pressure at the eardrum by approximately 12 dB at the major resonance at about 4,000 Hz." (Everest & Pohlmann, 2009).

Eardrum:

The eardrum is the first step in the process of converting air pressure waves into a liquid fluid movement. This movement is then converted to electrical impulses that are then sent to the brain to be processed as sound. "The conical eardrum at the inner end of the auditory canal forms one side of the air-filled middle ear." (Everest & Pohlmann, 2009).

Middle Ear:

The Middle Ear connects the Eardrum to the inner ear mechanisms. "The action of the middle ear is likened to two pistons with area ratios of 27:1." (Everest & Pohlmann, 2009). The middle ear is made up of "three ossicles (hammer, anvil, and stirrup) form a mechanical linkage between the eardrum and the oval window, which is in intimate contact with the fluid of the inner ear." (Everest & Pohlmann, 2009).

Round Window:

It provides pressure relief as the piston like mechanism of the middle ear moves the fluid in Cochlea. "The round window separates the air-filled middle ear from the practically incompressible fluid of the inner ear." (Everest & Pohlmann, 2009).

Cochlea:

Located in the inner ear is "The cochlea, the sound-analyzing organ, is in close proximity to the three mutually perpendicular; semicircular canals of the vestibular mechanism, the balancing organ." (Everest & Pohlmann, 2009). The mechanism of the middle ear creates movement "in the fluid-filled duct of the inner ear to stimulate hairlike nerve terminals that convey signals to the brain in the form of neuron discharges." (Everest & Pohlmann, 2009).

Semicircular Canals:

The Semicircular Canals are positioned above the Cochlea and consist of the "three sensory organs for balance that are a part of the cochlear structure." (Everest & Pohlmann, 2009).

Everest & Pohlmann (2009)

Safe dBSPL Exposure Time's:

The ability to hear is an important part of life. From detecting incoming danger to listening about a loved ones day its important to protect your hearing as its can be very easy to damage it. Organisations like Safe Work Australia have set standards for safe exposure time's at varying SPL's. They have outlined that being exposed to 85 dBA for 8 Hours per day is a safe level to prevent permanent hearing loss for most people. For every 3dBA over 85 dBA the exposure time is halved and every 3 dBA under 85 dBA the exposure time is doubled. (Safe Work Australia, 2015).

"Research shows that 8-hour average daily noise exposure levels below 75 dB(A) or instantaneous peak noise levels below 130 dB(C) are unlikely to cause hearing loss."(Safe Work Australia, 2015).

The (A) and (C) that they are referring to is the measurement weighting.

Safe Work Australia. (2015)

Group SPL Recording's and Data:

The following data was collected as a group effort on the 16th of November 2021. For each location we recorded with two TENMA Decibel Meters and the Decibel Meter iPhone application. One of the TENMA Meters was set to A weighing and the other was set to Z weighing along with the iPhone application was also set to Z weighing. All the meters were set to low level sensitivity and slow metering speed.

Through out all the measurements we as group noticed that the TENMA Meter I was using was displaying largely different readings to the iPhone application which was set to the same settings. We decided to test my meter against the other two and we discovered that even when set to the same settings my TENMA meter was significantly higher then the others. 3db difference. re calibration time is 1 yeah

https://drive.google.com/drive/folders/1-5uZC5izdDvBzl6GVBkyRmPt--QICL4e

SAE building rooftop:

TENMA - A Weighting dBSPL Average: 49 | Highest: 50.9 | Lowest: 48.8

TENMA - C Weighting dBSPL Average: 71 | Highest: 73.7| Lowest: 70.4

Decibel Meter - C Weighting dBSPL Average: 62 | Highest: 66 | Lowest: 61

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

Suitable recording location: No

The location is next to a road with light traffic and next to a river with heavy traffic on the other side. Besides man made sounds due to its elevation the wind is also a large issue and since its next a park you can hear it blowing through the trees along with the wildlife in them.

IMG_9806.MOV

Classroom/ Studio room:

TENMA - A Weighting dBSPL Average: 35 | Highest: 36.7 | Lowest: 34.3

TENMA - C Weighting dBSPL Average: 57 | Highest: 60.8 | Lowest: 55.2

Decibel Meter - C Weighting dBSPL Average: 46 | Highest: 52 | Lowest: 46

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

Suitable recording location: Yes

Beside this specific room being a "quiet" room if you were allowed to use it as a recording space it would be suitable noise pollution wise. Beside the general low hum of the buildings AC system if you turn off rooms dedicated AC It becomes an audibly quiet space. Although the foundation of a quiet room is present the acoustics are very lacking. There has been an attempt at acoustic treatment through the use of absorption panels on the walls how ever having a concrete wall on one side and glass windows on the other means these hard surfaces are very reflective to sound. This can be over come with the use of more acoustic treatment or in a pinch a blanket or two over the recording subject.

IMG_9810.MOV

Sidewalk next to a busy road:

TENMA - A Weighting dBSPL Average: 60 | Highest: 65.1 | Lowest: 56

TENMA - C Weighting dBSPL Average: 77 | Highest: 81.6 | Lowest: 74.7

Decibel Meter - C Weighting dBSPL Average: 72 | Highest: 79 | Lowest: 70

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

Suitable recording location: No

This location is next to a main road with construction occurring on the other side. Besides the sound of cars driving past the intersection also has pedestrian crossings with a rather loud alarm for when its safe to cross. The location is also in an industrial district surrounded by residential estate and park lands which each contribute their own noise pollution.

IMG_9812.MOV

Road across a river:

TENMA - A Weighting dBSPL Average: 52 | Highest: 65.6 | Lowest: 50.4

TENMA - C Weighting dBSPL Average: 69 | Highest: 74.3 | Lowest: 67.8

Decibel Meter - C Weighting dBSPL Average: 65 | Highest: 75 | Lowest: 63

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

Suitable recording location: No

Similar to the roof top location its positioned next to a lightly trafficked road and there is a heavy trafficked road across a river. It's also next to a park with wildlife and trees that pick up the wind. There is also a city cat terminal across the river which means ferries frequently passes by.

IMG_9811.MOV

Inside of a car:

TENMA - A Weighting dBSPL Average: 35 | Highest: 39.4 | Lowest: 33.7

TENMA - C Weighting dBSPL Average: 60 | Highest: 62.2 | Lowest: 60.1

Decibel Meter - C Weighting dBSPL Average: 53 | Highest: 60 | Lowest: 49

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

Suitable recording location: Yes

Although the car was parked on the lightly trafficked road next to the river with a busy road on the other side it was able to deaden most of all these noise sources. It's not perfect however but its protection against the wind and the acoustic absorption/ reflection of the cars interior makes a great recording location in a pinch if parked in the right place.

IMG_9813.MOV

Inside of a fire escape:

TENMA - A Weighting dBSPL Average: 39 | Highest: 81.4 | Lowest: 38.3

TENMA - C Weighting dBSPL Average: 62 | Highest: 95.6 | Lowest: 62

Decibel Meter - C Weighting dBSPL Average: 51 | Highest: 88 | Lowest: 50

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

Suitable recording location: No

The high verticality and use of concrete construction means this location has a lot of reflective surfaces and due to its size a large amount of reverb occurs with even the smallest of sounds. However if your looking for a natural reverb effect this location could be an interesting place to start. An idea could be to place a speaker at the top and place a microphone at the bottom or on different levels depending on the desired effect.

IMG_9808.MOV

Inside of a fire escape while making noise:

TENMA - A Weighting dBSPL Average: 75 | Highest: 87.4 | Lowest: 40.8

TENMA - C Weighting dBSPL Average: 87 | Highest: 100.8 | Lowest: 65.4

Decibel Meter - C Weighting dBSPL Average: 84 | Highest: 91 | Lowest: 56

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

Suitable recording location: No

This location was identical to the last however we decided to make a large amount of noise to see what the peek dBSPL we could produce was.

IMG_9814.MOV

Personal SPL Recording's and Data:

Inside my work's freezer room:

Decibel Meter - C Weighting dBSPL Average: 74 | Highest: 86 | Lowest: 73

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

Suitable recording location: No

The droning sound of the AC units is overpowering and makes it difficult to communicate with other people sometimes. And since its the inside of a freezer section at a super market there are doors that lead to the shop floor with customers who aren't always gentle when closing them. Along with the general fact that the room is at -20 decrees means you need PPE gear to be in there for any period of time. This gear also covers the ears adding to the difficulty to communicate.

Work_Freezer.mp4

Inside a club venue:

Decibel Meter - C Weighting dBSPL Average: 85 | Highest: 92 | Lowest: 63

Safe exposer time: Unsafe

The average dBA does exceed 85 meaning you should limit the exposure time to 8 hours per day to reduce permanent hearing loss.

Suitable recording location: No

Besides the fact that its a club that hosts live performances there is also a busy major road directly out side the building. Meaning even if you turned down or off the main speakers there will still be the presents of noise pollution from the road outside and neighboring clubs. If however you are looking for that grungy live performance sound this could be a suitable location but for any other types of recordings if would not be. The room itself is very long and narrow with drywall on all sides and concrete flooring.

Club.mp4

The ambient room noise of my office:

Decibel Meter - C Weighting dBSPL Average: 32 | Highest: 41 | Lowest: 32

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

Suitable recording location: Yes

The only issue with this location is its positioned near a train line with constant freight trains passing by. Other then that its located at the end of a residential street and next to large open fields resulting in very low noise pollution. The room itself in located in the middle of the house on one side meaning its as far away from the front and rear of the building as possible. There has also been an attempt to acoustically treat the room with the use of DIY absorption panels and carpeted flooring. The position of the three computer monitors is not optimal for recording as they reflect a large amount of sound if recorded that the desk as is usually the case along with the hard wood desk.

Office_Ambient.mp4

In my office listening at a high level:

Decibel Meter - C Weighting dBSPL Average: 80 | Highest: 87 | Lowest: 73

Safe exposer time: Unsafe

The average dBA does exceed 80 meaning you should limit the exposure time to 16 hours per day to reduce permanent hearing loss.

This is an example of the average max volume used when I am listening to music at my computer during the day when I want to really listen to a song.

Office_Music_Loud.mp4

In my office listening at a normal level:

Decibel Meter - C Weighting dBSPL Average: 70 | Highest: 79 | Lowest: 54

Safe exposer time: Safe

The average dBA does not exceed 80 meaning there is no exposure time limit.

This is an example of the average volume used when I am listening to music or watching YouTube at my computer normally or at night time. This is also the volume used when editing videos.

Office_Music_Normal.mp4

Conclusion:

It was interesting looking at the ambient noise of different locations and how loud they actually are to record in. This project has tempted me into getting an actual level meter so I can keep track of my recording space over time and keep it constant. I spend a bit of time in the work freezers so it's good to know that they aren't damaging to the ears. It was also good to see that my office has a low enough ambient noise floor that i'm happy with as a recording and leisure place. The biggest take away I've gained from this project is that cars make for great recording locations if parked in the place for instance if it were in a garage you could probably walk away with some vary usable takes.

Reflection on DATA, Process and Feedback:

As this was the first project I was able to work with others on it was enjoyable to collect and reflect on data with like minded people. The data collection process went really smoothly as the three of us had similar ideas about recording locations and went to work collecting the data. Granted it was a little awkward having the three of us in the fire escape making a lot noise for half a minute but it was fun and we got some interesting data from it. As for the other locations we all understood how to use the equipment and what data we needed and worked well together to collect it.

Initially I was partnered with someone who had left so I started to work on the project alone and collected some of my own data that I thought could be interesting to analyse for instance my work freezers and my home office. It was good to see that I wasn't damaging my ears with the volumes that I sometimes listen to music at nor that my works freezer were damaging them either. This project has made me even more aware of little sounds and their sources and has opened my ears and understanding on how to measure them/ negate them. As feedback goes in class Beau helped me again with intext referencing and helped me with referencing as a whole in my data section.

Initially I had struggled to find authoritative sources of information regarding the human ear that were written in a way I could comprehend. David suggested the book "Master Handbook of Acoustics 5th ed". (Everest & Pohlmann, 2009). This book provided me with all the information I needed in a way that was easy for me to comprehend and learn from. At first I had no interest in learning about the human ear due to my disliking of biology (its gross). However after doing research I started to find it interesting how all the different mechanisms work together and how complex of a structure it is. The middle ear was intriguing to me in how "The action of the middle ear is likened to two pistons with area ratios of 27:1." (Everest & Pohlmann, 2009). I've always had a deep interest in mechanics so being able to see similarities between physical and biological mechanisms was interesting.

References:

Berg, R. (2000). acoustics | Definition, Physics, & Facts. Encyclopedia Britannica. Retrieved 25 November 2021, from https://www.britannica.com/science/acoustics#ref527537.

Centers for Disease Control and Prevention. (1998). Occupational Noise Exposure [Ebook]. Retrieved 21 November 2021, from https://www.cdc.gov/niosh/docs/98-126/pdfs/98-126.pdf?id=10.26616/NIOSHPUB98126.

Decibel Meter. (2021). Decibel Meter Sound Detector. App Store. Retrieved 21 November 2021, from https://apps.apple.com/au/app/decibel-meter-sound-detector/id1254994873.

E-Home Recording Studio. (na). Fletcher Munson Curve: A Must-Know for Audio Recording. E-Home Recording Studio. Retrieved 25 November 2021, from https://ehomerecordingstudio.com/fletcher-munson-curve/.

Everest, F., & Pohlmann, K. (2009). Master handbook of acoustics (5th ed.). McGraw-Hill.

H., J. (2021). Fletcher Munson Curve: The Equal Loudness Contour of Human Hearing. LedgerNote. Retrieved 25 November 2021, from https://ledgernote.com/columns/mixing-mastering/fletcher-munson-curve/.

Hawkins, J. (2002). human ear | Structure, Function, & Parts. Encyclopedia Britannica. Retrieved 22 November 2021, from https://www.britannica.com/science/ear.

Hosch, W. (2006). sound-level meter | instrument. Encyclopedia Britannica. Retrieved 25 November 2021, from https://www.britannica.com/technology/sound-level-meter.

Humes, L., Joellenbeck, L. M., Durch, J., & Institute of Medicine (U.S.). Committee on Noise-Induced Hearing Loss and Tinnitus Associated with Military Service from World War II to the Present. (2006). Noise and military service : implications for hearing loss and tinnitus. National Academies Press. Retrieved November 19, 2021, from https://ebookcentral.proquest.com/lib/sae/reader.action?docID=3378025#.

Humes, L., Joellenbeck, L., & Durch, J. (2006). Noise and military service. The National Academies Press. Retrieved 21 November 2021, from https://ebookcentral.proquest.com/lib/sae/reader.action?docID=3378025.

NTI. Audio. (na) Frequency-Weightings for Sound Level Measurements. Nti-audio.com. Retrieved 25 November 2021, from https://www.nti-audio.com/en/support/know-how/frequency-weightings-for-sound-level-measurements.

Safe Work Australia. (2015). MANAGING NOISE AND PREVENTING HEARING LOSS AT WORK. [ebook]. Retrieved 22 November 2021, from https://www.safeworkaustralia.gov.au/system/files/documents/1702/managing_noise_preventing_hearing_loss_work.pdf.

Suzuki, Y. (2003). Precise and Full-range Determination of Two-dimensional Equal Loudness Contours. Web.archive.org. Retrieved 25 November 2021, from https://web.archive.org/web/20070927210848/http://www.nedo.go.jp/itd/grant-e/report/00pdf/is-01e.pdf.

TENMA. (2021). Sound level Meter. Element14. Retrieved 21 November 2021, from https://au.element14.com/tenma/72-942/meter-sound-level-30db-130db-1/dp/2083810.

Van, D. W. T. R. (2012). Historical aspects of inner ear anatomy and biology that underlie the design of hearing and balance prosthetic devices. Anatomical Record (Hoboken, N.j. : 2007), 295(11), 1741–59. https://doi.org/10.1002/ar.22598.

Page updated

Google Sites

Report abuse