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In order to understand how the Human Ear and hearing works, it is imperative to  first understand how sound waves work.

Sound waves are a acoustical phenomena which are created from the vibrations and following displacement of particles in whatever body in which the vibration is occurring.

Sound waves are Longitudinal in nature, meaning that the displacement of particles is parallel (and anti parallel) to the source of the energy transfer, which caused the vibration.

Wavelength-This is the time taken for a sound wave to carry out one full “cycle” through whichever body of matter in which it is traveling, a “cycle” refers to the wave completing one “compression”, (therefore rising in amplitude  displacement before culminating in a peak/crest) before descending back to the basal amplitude (then engaging in a refraction, which follows essentially the same path, but in reverse).In short, the Wavelength is the actual length of the wave, with higher frequencies having shorter wavelengths and lower frequencies having longer ones. The speed of sound is 1125 feet per second, with this we can work out the wavelength of any frequency, eg: 1125/440hz (A4)=2.5 feet. 1125/110hz (A2)=10.2 feet. Wavelength is symbolized by a Lambda ("λ")  and is generally plotted along the "X" axis of a graph.

Amplitude-This is the actual strength of a sound wave, the higher the amplitude is, the higher the volume of the sound vibration wave. This is dependent on the intensity of the vibration which created the sound wave. Amplitude is generally plotted against the "Y" axis of a graph and is displayed as the distance between the sound waves "crest" and the sound waves "trough".

Frequency-this term refers to how many times that the wavelength "cycles" occur per second, the unit used for frequency is "Hz" or "kHz", each "Hz" refers to one complete cycle, sounds which are higher in pitch are higher in frequency and pitches lower in pitch are lower in frequency; eg: 110hz is the second octave of the note "A", and its frequency is 110 full cycles in a second, 440hz is the fourth octave of the note "A" and is therefore a higher frequency than the aforementioned "A2" and its frequency is 440 cycles per second.
fig.1

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The harmonic series is a sequence of pitches which are mathematically related positive integers derived from the fundamental pitch (aka: first harmonic) or root note.
The term 'Overtone' is used to describe any frequency above the lowest 'partial' (any one of the many sine waves which make up a 'complex tone'-the timbre of an individual instrument). The term 'Overtone' does not imply whether a tone is harmonic or inharmonic. 'Inharmonic' tones are tones which are not mathematically related to the integer of the fundamental pitch, or deviate from he multiples of this pitch (harmonic series) as a result, these tones may affect the sound of the instrument but are not necessarily unpleasant. Inharmonic tones may be prevalent in untuned percussion instruments and to a lesser extent, string instruments (which have a sawtooth wave form).
Generally, the more Harmonics from the Harmonic Series that are present in a tone, the richer and fuller its tone, this is referred to as a "Complex Tone" and it defined as a tone specific to the instrument being played

The formulae for working out the harmonic series is as follows:

Fundamental pitch (Hz) x degree of harmonic series  (1,2,etc) = frequency of degree of harmonic series (Hz)

Eg: 110 Hz x 2 = 220Hz (2nd harmonic/1st overtone)

Whilst individual overtones can be difficult to discern from the fundamental pitch , with ear training it is possible to do this.

fig.2

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The human ear is an organ which allows humans to systematically detect, distinguish and determine the distance/direction of sound pressure waves.
The anatomy of the human ear is generally broken down into three sub sections, the outer ear, the middle ear and the inner ear.

The Outer Ear-the outer ear is shaped rather like a funnel and has a large surface area, along with a series of curves and ridges (such as the Pinna). These aid in the triangulation of the source of the sound pressure waves, the Pinna, for example, aids in locating the source of a sound pressure wave in terms of the vertical plain (whilst also protecting the ear to an extent).
When Sound pressure waves are received in the outer ear, they travel up the 'Acoustic Meatus' or 'Ear Canal' towards the middle ear.

The Middle Ear-the middle ear is tunnel like structure through which sound pressure waves travel after passing through the outer ear, the sound pressure waves travel through the Ear Canal (Acoustic Meatus) before coming into contact with the Ear Drum (Tympanum), this in turn causes the Ear Drum to vibrate and converts the acoustic energy of the Sound Pressure Waves into Kinetic energy/vibrations.
These Vibrations, in turn cause the chain movement of the three smallest bones in the human body (the Malleus/Hammer, Incus/Anvil and the Stapes/Stirrup), this is referred to as the Ossicular Chain
The last bone in the middle ear (Stapes) then strikes the fluid in the membrane in the Cochlea.

The Inner Ear -The Cochlea is a tunnel like structure (it has a single main chamber and two smaller ones) which is coiled around itself, resembling a snail shell in appearance. When the membrane of the Cochlea is struck by the Stapes, the fluid inside the Cochlea travels further through the the main chamber, the distance which this fluid travels into the Cochlea is dependent on the Wavelength of the Sound Pressure Wave which is triggering the reaction (Lower frequency waves have a longer wavelength and therefore travel farther down the chamber, Higher frequency waves have a shorter wavelength and do not travel as far down the Cochleas chamber). The movement of this fluid (Perilmyph) triggers the movement of tiny, Wavelength sensitive hair cells inside the Cochlea (Stereocilia), the movement of these hair cells is converted into electrical signals which trigger the auditory nerve and send the information to the brain where all of the information (timbre, pitch,etc)  is processed in milliseconds.

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The causes of hearing loss and preventative measures against it

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The causes of hearing loss and preventative measures against it

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Hearing loss is defined as the partial or total inability to hear, it can be temporary or permanent, painful or painless, affecting one ear or both and can be contracted through natural or man made causes, the following is list of causes which Musicians are most likely to experience.

* NIHL (Noise Induced Hearing loss)-This is one of the most common and relevant causes of hearing loss among musicians, this type of hearing loss is caused by sustained periods of exposure to noises over 85 decibels (City traffic/motorcycle engine/loud headphones/venue speaker systems/etc). It can also be caused by one-time exposure to extremely loud noises eg; bursts of feedback, explosions, etc.
These two types of exposure can null the effectiveness of the "Acoustic Reflex" (AKA: Stapedius Reflex, the ear internal mechanism for preventing damage to its sensitive inner workings and therefore hearing loss), without this system, loud noises can damage or kill off the Stereocilia, resulting in a lack of clarity or volume this can result in conditions such as tinnitus, partial/total hearing loss.
Prevention: The best solution to combat hearing loss is to take preventative measures, if you or other musicians are working in a live setting or any other setting in which the volume you'll experience will be over 85 decibels hearing protection should be worn, the following is a link to UK based organisation which offfers quality, custom earplugs for musicians for the novel fee of £40  (£30 for Musicians Union members). https://www.hearformusicians.org.uk/.
There is however some medical therapy available to individuals who have already suffered hearing loss, from simple acoustic therapy and medication to ensure damaged hair cells dont die, to wholly innovative regenerative research techniques pioneered by 'Frequency Therapeutics'.

* Ear infection (Otitis Media)- This is when the ear contracts an infection, this results in a buildup of fluid inside the Middle Ear which prevents the Eardrum or the Ossicular Chain  from functioning properly, this phenomena is quite painful, though the type of hearing loss that occurs from this is generally short term, however if left untreated, the buildup of fluid can cause the ear drum to rupture.
Recurring ear infections can also lead to 'tympanosclerosis', this is the thickening and scarring of the tympanic membrane. A perforated eardrum and/or 'tympanosclerosis' can severely impede the movement and function of the ear drum and consequently your hearing.
Prevention: To prevent ear infections, it is advisable for musicians to practice good aural hygiene to prevent the buildup of wax/dirt (which can also cause hearing loss) and lower the risk of infection. If you do suffer from an injury/ infection of the ear it is advisable to contact your local GP and seek professional medical help.

*Other Causes: It is noteworthy that hearing loss is inevitable and the degradation of the Stereocilia is natural occurrence, we can only seek to prolong the lifespan of them. Other factors which may cause hearing loss include:
* Medication-Large doses of Aspirin, Ibuprofen and certain antibiotics
*Hereditary-Genetics play a prominent role in the lifespan and durability of Stereocilia.

fig.4

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Myself and a fellow class mate conducted an experiment to show how placing the microphones in a manner similar to the position of the human ear would affect how sound was perceived. We used 2 DPA 4090 microphones and placed them at either side of my classmates head (beside his ears, again to simulate how sound is picked up by the human ear).
During the experiment I played guitar in the left side of the room first, then moved to the front and then to the right side of the room.
Our hypothesis was that the microphones would simulate how the human ears pick up sound waves and therefore the left microphone would pick up the sound waves before the right microphone (when I played at the left side of the room).
We noticed when the sound source (me playing guitar) was in front of the microphones the sound waves were picked up by the microphones at the same time, therefore the audio sounded more equal in terms of panning (implying that the sound source had moved in front of me, which it had) compare this when the sound source was at the left or right of the microphones, in which case the sound of the guitar was more dominant in the respective microphone
After analyzing  the audio that was recorded we could conclude that our hypothesis was infect correct. To show this was the case I have included a screenshot of the audio that was recorded. In this screenshot the top sound wave was the right microphone and the bottom the left microphone, at the time of this screenshot, the sound source was in the left side of the room. You can clearly see that the left microphone picked up the sound first and right microphone (top) had a delayed effect, this is called inter-aural delay and this is how humans can perceive sound being from different directions.

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fig.5
-top line=Right Microphone
-bottom line=Left Microphone

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Picture showing mic position in relation to classmate

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Picture showing mic position in relation to classmate

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fig. 6

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Picture showing source of sound in relation to microphones:

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Picture showing source of sound in relation to microphones:

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fig.7

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I was tasked with producing a padlet document which accomplished the following:
.1 Explain the physiology of hearing and the causes for loss of hearing |
| 2.2 Explain the principles of localization and perception of distance
I believe that I have competently explained both of these criteria, however if I could redo the task I would've started earlier in order to create a more comprehensive and extensive Bibliography, one in the Harvard referencing style.
Ideally, I would have also completed the pass criteria from previous assignments, as I found it quite difficult to integrate the harmonic series into the topic of human hearing.
I believe that myself and my classmate carried out our experiment to the best of our ability considering the time constraints.

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* https://www.nidcd.nih.gov/health/noise-induced-hearing-loss
* https://www.starkey.com/blog/2017/05/Ear-infection-caused-hearing-loss
* https://www.hearformusicians.org.uk/
* https://www.webmd.com/a-to-z-guides/tc/medicines-that-cause-hearing-loss-topic-overview
* http://www.hearingreview.com/2017/02/study-shows-hair-cell-regrowth-new-drug/
* https://www.youtube.com/watch?v=8KgtQHbQnDk
* https://www.youtube.com/watch?v=XPbLYD9KFAo
* https://www.nhs.uk/conditions/hearing-loss/
* http://www.hearingloss.org/content/types-causes-and-treatment
*http://zone.ni.com/reference/en-XX/help/372416B-01/svtconcepts/human_perception_sound/
*http://www.sengpielaudio.com/calculator-harmonics.htm
* https://youtu.be/3G5jiXl2LSM
* https://www.mayoclinic.org/diseases-conditions/hearing-loss/symptoms-causes/syc-20373072