Sound Flashcards
Define the term Sound
sound is defined as vibrations emitted from a source that excites similar movement in air molecules and results in pulses of increased pressure that moves out from the original source. This vibratory energy travels in waves that move through the air or any other medium and from one medium to another.
What is meant by the terms frequency
Frequency and Sound are characteristics of sound
Frequency is defined as the number of times a periodic quantity repeats itself. It is a physical expression of quantity a rate of which wave disturbances that repeat itself.
The measuring unit the second is one of time and frequency is expressed as hertz but pitch is subjective and expresses sensory perception in the mind of the listener the normal human ear can hear sounds from 20 to 20000hz or cps
What is meant by the term Intensity
Intensity relates to power or pressure of the sound wave. The greater the power or pressure the louder the sound. Loudness is a sensory perception in the mind of the listener
What are sounds called that occur at only one frequency
Puretones
What is noise
Noise is unwanted sounds. Sound as noise is subjective assessment and often depends on the individuals attitude about the source and the nature of the sound
Explain the two primary features of the decibel scale
- The decibel scale is based on ratios. The reference quantity for expressions of decibel in sound pressure is 0.00002 N/M/2 0.00002N/M2 is 0 db. decibel is a ratio between a given sound pressure and a specified reference pressure the faintest sound a human can hear 0db
2 The decibel scale is logarithmic and based on powers of ten. Thus each 10db increase is equal to increasing the relative energy, intensity tenfold
Why cant decibel levels be added combining noise level readings to determine whether workers are noise exposed
Because the decibel is based on logarithms two or more decibel levels cannot be added to arrive at a sum of decibels
if two adjacent machines have a sound level reading of 90dba the combined noise level will increase by 3 decibels not by 90dba the level is not the two individual decibel readings.
Which weighing network has the frequency response characteristics closest to those of the human ear
The A-Weighted network has frequency response characteristics that are most similar to those perceptible to the human ear. A sound level survey includes measurements of sounds in decibels on the a weighted network DBA
What is the purpose of DRC
to protect the majority of workers from becoming hearing impared
What are 2 major sets of DRC
- The 5db trading relationship
- The 3db trading relationship
Damage risk criteria is expressed as allowable exposure times relative to dba levels
The trading relationship trades allowable time which always decreases by half for each 3 or 5 increased noise levels
What is the basis for 5db trading relationship
The 5 db. trading relationship is based on lab studies of temporary threshold shifts the relationship considers the fact that hearing loss or threshold shift due to noise exposure is temporary, provided that the ear has time to rest this means experiences no noise exposure then it will recover. The TTS studies demonstrated that greater TTS is generated by continuous exposure to noise than from intermittent exposure therefore intermittent exposure was determined to be less hazardous
What is the basis for 3 db. trading relationship
The 3 db. trading relationship is based on equal energy theory that states that equal amounts of A weighted energy cause equal amounts of hearing loss regardless so whether the exposure is constant or intermittent and regardless of whether the Nosie is impact noise or steady state noise when using this type of DRC, exposure to 85 DBA for 8 hours is equivalent to 88 DBA for 4 hours or 91 DBA for 2 hours 94 DBA for 1 hour and so on
What is a threshold shift
A threshold change at any frequency is known as a threshold shift. To find out if a workers hearing threshold has changed, you will need at least two hearing tests for that worker on which to base the comparison
What is a common complaint with someone who has noise induced hearing loss
I can hear you just fine but its just not clear the words are distorted
In speech and conversation what are the high frequency sounds
the frequency sounds include the consonants S, K, t, th, ch, P
How is the occupation injury in noise induced hearing loss described
Painless,
No Visible Signs
Slow to progress
100% permanent
Preventable
What are two parts of the external ear
The external ear is made up of the pinna the Auricle and the external auditory canal
what is the function of the external ear
to collect and funnel sound waves and to protect the ear drum
What are some of the problems that can occur in the external ear
impacted wax
skin issues like dermatitis
Stenosis narrowing of the auditory canal from injury or infections
What does the sound conducting mechanism of the middle ear consist of
The eardrum, Malleus, Auricle, Incus, the ligaments, tensor timpani, stapedial
How does the sound conducting mechanism work
The eardrum is sensitive to minute sound pressure disturbances that cause the eardrum to vibrate. The vibration of the eardrum is transferred across the ossicles to the oval window and thus from the outer ear canal to the inner ear. Sound energy in air is transformed to mechanical energy in the middle ear.
What happens to the sound energy as it is transmitted from the outer ear to the inner ear
As sound is transmitted it is amplified
The eardrum where vibration occurs enters the middle ear (which is much larger than the oval window where the vibration exits the middle ear
The ossicles which act as levers increasing the sound energy because of these two mechanisms the sound is increased by 20 times the original volume
What are some common middle ear disorders
infection
perforated ear drum
otosclerosis
break in the ossicles
What structures make up the inner ear(labyrinth)
The bony Labyrinth consist of the cochlea, , semicircular canals, vestibule a fluid called perilymph fills the bony labyrinth, the other is called the membranous labyrinth is within the bony labyrinth and consist of the balance organs the cochlear duct a fluid called end lymph fills the membranous labyrinth
What are two functions of the inner ear
Maintaining balance and hearing
How does the inner ear transfer sound energy
at the oval window fluid conduction of sound energy begins
Vibration of the oval window causes vibration in the perilymph this vibration is transferred to the endolymph within the cochlear duct The membranous cochlear duct contains the receptors or hair cells that are attached to the nerve endings when the fluid vibrates the hair cells stimulate the nerve endings that send an electrical impulse to the brain
Where in the cochlear are high frequencies detected and where are low frequencies detected
High frequencies are detected by the hair cells that are close to the oval window Hair cells that are further away from the oval window detect lower frequency sounds and the lowest frequency sounds are detected at the apex of the cochlea the furthest from the oval window
What type of hearing loss is generally caused by problems in the external ear and middle ear
Conductive
What types of hearing loss is generally caused by problems in the inner ear
Sensor neural
What are the most common causes of sensorineural hearing loss in adults
Noise induced hearing loss and aging
What are the two main causes of hearing loss in the workplace
Excessive noise exposure and acoustic trauma from blast or explosion
Acoustic trauma can damage the middle and inner ear
Noise effects the hair cells within the ear
temporary and permanent threshold shifts can result from noise and acoustic trauma
What is temporary threshold shift
It is a hearing loss that will recover
the recovery depends upon the extent of the damage to the ear and the extent of the shift. the greater the TTS from noise exposure the longer the recovery time is needed until pre exposure thresholds are returned The rest period for moderate exposure is 12-14 hours
What are some characteristics of NIHL
- NIHL is gradual it occurs from repeated exposure over many years. Permanent loss can occur between 5 to 20 Years
- The first shift is between 4000HZ and or at 6000HZ this is called a notch or a dip the hearing loss at the lower frequencies will remain the same then at 4000 and or 6000 there will be a drop
- the worker is not usually aware of the early effects of NIHL its only at the speech frequencies that NIHL is evident to the individual even at the speech range many people still get by and don’t acknowledge the seriousness of the damage.
- NIHL is not painful
- NIHL is permanent and can’t be corrected with medication or surgery
- Hearing aids don’t restore normal hearing
- NIHL is not evident externally the damage is not visible to others
What are some direct extra auditory effects of noise
Noise is a source of stress and the body reacts as it does to other stressful situations direct physical effects include: Increase in blood pressure , changes to heart rate, hormone levels and blood cholesterol. excessive noise can cause irritability and fatigue
effect work performance and put worker at risk
What do you think are some extra auditory effects
NIHL effects Interpersonal communication workers can lose their ability to communicate in many social situations and may begin to progressively isolate themselves. This can effect them not only psychically, but emotionally and socially.
What is the sudden loud noise from gunfire called
Impact
What is the technical term for ringing in the ears
Tinnitus this is a otological condition in which sound is perceived by a person without the external auditory stimulation
Name two sources of noise that could contribute to hearing loss
chain saw, motor bike, rock concert, hunting rifle,
