Download Inner Ear - Truth Recordings

AUD202
Audio and Acoustics Theory
The Human Ear and the Hearing Process
Noise Induced Hearing Loss
Hearing Protection
OH&S Principles
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Musical Instruments and Sound
Standing Waves in String and Pipes
Envelope of sound
NIHL report
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25 Days - NIHL Report
46 Days - Sound Observations Report
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Comb filtering is caused
by a wave combining with
a delayed version of itself
Comb Filters
The mathematical relationship between the nulls is they are odd
harmonics of the fundamental
The mathematical relationship between the
nulls of a comb filter is: they are odd
harmonics of the fundamental
The peaks are even harmonics of the
fundamental
ADSR (Attack, Decay, Sustain, Release)
Standing Waves in String Instruments
The standing wave constraint of string
instruments is that at each end of the medium
there must be a node.
String instruments produce a fundamental
plus odd and even harmonics
Standing Wave Constraints
String instruments have a node at each
end of the string.
Open wind instruments have an anti node
at each end of the pipe.
Open closed wind instruments have a
node and an anti node.
HEARING AND THE EAR
Fields Related to Hearing
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Artistic (Music, Sound Art)
Audio Engineering (Live, Studio)
Media (TV, Radio, Film, Games etc)
Physics (Properties of Sound)
Acoustics (Architecture, Sound Engineering)
Psychoacoustics (Research, Audio Codecs,
Localisation, Perception)
• Medical (Audiology)
• Communication
• Academic (Research, Teaching, Learning)
Absolute Threshold of Hearing
The threshold of hearing is the minimum sound level
of a pure tone that an average ear with normal
hearing can hear with no other sound present.
The reference for 0dB SPL is defined as the ‘threshold
of hearing’ of a young undamaged ear in the ears
most sensitive range - between 1kHz and 4kHz.
Threshold of Pain
The Threshold of Pain is the pressure at which sound
becomes painful for a listener
120dB is generally the threshold of pain
Anatomy of the Human Ear
• The three main sections of the ear are:
the Outer Ear, Middle Ear and Inner Ear
• The ear changes sound pressure waves from the
outside world into nerve impulses sent to the brain
Stereocilia
Stereocilia
Stereocilia
Figure: Dead receptor cells (n.d.)
Stereocilia
Malleus
Hammer
Incus
Anvil
Stapes
Stirrup
Tympanic
Membrane
Eardrum
Anatomy of the Human Ear
The outer ear collects sound. The sound pressure
is amplified through the middle ear and passed
from air into liquid. The inner ear changes
soundwaves into nerve impulses. The nerve
impulses travel along the auditory nerve to the
brain.
It also helps us with balance and positioning
Figure: The ear (Palmer 2003)
Outer Ear
The pinna and the external auditory canal are part of
the outer ear
Sound Waves travel through the external auditory
canal, strike the tympanic membrane (eardrum) and
causes it to vibrate
The external ear selectively boosts frequencies around
3 kHz. This makes humans most sensitive in this range
and makes us prone to acoustical injury and hearing
loss near this frequency
Middle Ear
Sound waves travelling through the external auditory
canal will:
(1) Hit the eardrum causing the
(2) hammer, anvil and stirrup bones to move
(3) the stirrup bone shakes part of the cochlea
changing the pressure in the air to pressure in liquid
(inside the cochlea)
Inner Ear
The cochlea converts sound pressure impulses
from the outer ear into electrical impulses which
are passed on to the brain via the auditory
nerve.
The vestibular system is dedicated to balance
EQUAL LOUDNESS CURVES
Equal Loudness Curves
Equal-loudness Curves are a measure of sound
pressure (dB SPL), over the frequency spectrum,
for which a listener perceives a constant
loudness when presented with pure steady
tones.
Equal Loudness Curves
The unit of measurement for loudness levels is
the phon and is arrived at by reference to equalloudness contours
NOISE INDUCED HEARING LOSS
Typical progression of NIHL (over 40 years) (n.d.)
In Australia it is estimated that 37% of all hearing
loss is a result of noise exposure (Access
Economics, 2006), and The Australian Safety
and Compensation Council estimates that 1
million Australian workers are potentially exposed
to dangerous noise levels each year and that
compensation claims in 2001/2 for occupational
noise induced deafness accounted for direct
costs of $30 million, which it further estimates to
be less than 10% of the total cost of noise.
(Australian Safety and Compensation Council,
2006).
According to Safe Work Australia (2004), the national standard for
occupational noise exposure is eight continuous hours at 85db at an Aweighted
sound pressure level, anything above this is deemed to be a high risk
cause of NIHL. Whilst not the number one work related health condition, NIHL is
still a fairly common occurrence amongst Australian workers with approximately
four hundred and sixty nine out of every one million employees having made a
compensation claim in the period between 2007 and 2008 (Australian Bureau of
Statistics (ABS) 2011). This makes NIHL the third highest work related health
condition in Australia and shows the extent of the problem within the workforce.
Thurston (2012) states that NIHL came about
with the invention of gunpowder and the arrival
of the Industrial Revolution in which introduced
new sounds of greater intensity than ever
before.
First signs of hearing loss are a notch or reduction of
hearing frequencies at around three, four and six
kilohertz (KHz) and are most commonly bilateral.
Tinnitus
Tinnitus is the condition of ringing in the ears when no
other noise is present.
Noise Induced Hearing Loss
• Hearing loss can be described as congenital (from
birth) or acquired. NIHL is acquired.
• Exposure to loud sound can cause the hair cells in
our inner ear to be damaged, resulting in noiseinduced hearing loss
• Hair cells are small sensory cells that convert sound
energy into electrical signals that travel to the brain.
Once damaged, hair cells cannot grow back.
Hearing Loss
• Conductive Hearing Loss is caused by
blockage or damage in the outer and/or
middle ear (i.e. middle ear infection)
• Sensorineural Hearing Loss is a result of
damage to, or malfunction of the cochlea or
the hearing nerve
Noise Damage Indicators
If sounds seem muffled or softer after noise
exposure, your hearing has been affected by a
temporary threshold shift, which warns that your
hearing has been overexposed.
If you repeatedly do this without protection, the
shift can become permanent and untreatable.
Incidence of hearing loss by profession (n.d.)
Hearing Protection
Earplugs
Earmuffs
Noise Isolating headphones
Noise-cancelling headphones
Preventing NIHL
Restrict exposure to less than 90dB for a maximum of eight
hours per day (Palmer 2003, p. 43).
Set volume levels on devices paired with headphones
(preferably over-ear type) up to 70% volume, for a
maximum session duration of around 4.5 hours (Levey et al.
2013, p. 300).
Use ear protection whilst attending loud events or doing
work in industrial environments (Reid 2005, p. 54).
OH&S Principles
• Understand the noise level exposure time chart and
recognise when you are damaging your hearing
• Limit your exposure to loud noise, otherwise protect
your ears with hearing protection
• Use your knowledge to help protect others, e.g.
young children, musicians etc
Audio Engineering Society
www.aes.org
Username: jmcacademy
Password: student1
Next Week >
The Decibel
dBSPL, dBV, dBu, dBm
The Inverse Square Law
SPL Meters
References
Dead receptor cells n.d., PNW Audiology, United States, viewed 15 November 2013,
<http://www.pnwaudiology.com/noise-induced-hearing-loss>.
Incidence of hearing loss by profession n.d., Audicus, United States, viewed 7 November 2013,
<http://www.audicus.com/blogs/hearing-aids-blog/6071738-the-shocking-data-about-noise-induced-hearingloss-in-the-workforce>.
Levey, S, Fligor, B, Cutler, C & Harushimana, I 2013, ‘Portable music player users: cultural differences and
potential dangers’, Noise & Health, vol. 15, no. 66, pp. 296-300.
Typical progression of NIHL (over 40 years) n.d., Better Hearing, United States, viewed 21 November 2013,
<http://www.betterhearing.org/hearing_loss_prevention/noise_induced_hearing_loss/>.
Palmer, AR 2003, ‘How the ear works and why loud sounds cause hearing loss’, paper presented at the AES UK
18th Conference: Live Sound, April 2003.
Reid, AW 2005, ‘Notes of caution’, The Safety & Health Practitioner, vol. 23, no. 9, pp. 51-55.