Noise & Vibration Flashcards
Sound Power
The total energy radiated by the source per unit time
Sound Pressure
The root mean square value of the pressure changes above and below atmospheric pressure.
White Noise
Random Spectrum with a random energy per unit frequency over a specified frequency band.
Pink Noise
Greater energy per frequency
Pure Tone
Single frequency
Reverberant field
reflected sound from walls
Free field
no reflective surfaces
Direct Sound Field
direct path to receiver
Outside noise
can be perceived as annoying if it exceeds background noise by 10 dB
Signals
Sounds 10-15 dB above background
Doubling Sound Power
6 dB change in SPL
Vibration
Most damaging frequency 1-125 Hz
3 intities of sound
Power (W) = Time rate of work (Watts) , Constant
Intensity (I) = Amount of Work over area (Watts/Area), Follows Inverse Squares
Pressure (P) = Usually what is measured ,I P2 , Follows inverse squares
Outer parts of the ear
Pinna (sound gathering/directional),
Ear Canal, (excretes wax, acts as a tubular resonator)
Tympanic Membrane (eardrum)
Middle parts of the ear
Ossicles - mallus, Incus, and Stapies (attached to oval window)
Estuation tube – equalizes the pressure between the oval and round windows
Inner Transduction
liquid to electro-chemical
Parts
- Cochlea
- Organ of corti (attached to 8th cranial nerve)
Transmission of sound
Stapedial footplate moves the oval window in and out moving the perilympth of the scala vestibule Vibratory activity moves up the scala vestibule causing a downward distortion in the reissner‘s membrane and displacement of the endolympth of the organ of corti.
Vibration of the basilar membrane causes a shearing (pulling) force on the hair cells against the tectorial membrane (process is called transduction). This force activates the nerve endings of the hair cells.
Activity is transmitted through the basilar membrane to the scala tympani. The oval window acts as a relief point by bulging out as the oval window bulges in.
Conductive Hearing Loss
- Condition interfering with transmission of sound to the cochlea
- Can be due to wax, blockage of estuation tube, interruption of ossicular chain due to
trauma or disease, infection of inner ear, otosclerosis
Sensor neural Hearing Loss
- Almost always irreversible
- Organ of corti or neural impacts of auditory nerve
- Exposure to excessive noise, presbycusis, viruses (i.e. mumps) and drug toxicity
Mixed hearing loss
Elements of both conductive and sensor neural
Central hearing loss
- Ability to interpret speech
- Localized between brain and auditory nerve
Psychogenic
“Non-Organic”, malingering or hysteria causes
Sound Level Meters
Dynamic – mylar
Ceramic – crystals – Piesoelectric sound, moisture effects it
Condenscer - capacitor (best type)
Sound Level Meter Types
Type I (precision) ±1 dB @ 1000 Hz Type II (general Survey) ±2 dB @ 1000 Hz Type III ( Field) ±3 dB @ 1000 Hz Type IV (Special) ±4 dB @ 1000 Hz
Noise Induced Hearing Loss (NIHL)
predominate @ 3000-4000 Hz, Hearing loss occurs – 10-20 years
Presbycusis
A gradual loss of hearing due to age. A person with presbycusis can often not hear frequencies > 3,000Hz.
Recruitment
condition, which impairs the ability to hear faint or moderate sounds but leaves the detection of loud sounds intact. An increase of 3 dB represents a doubling of the sound intensity (loudness)
Standard Threshold Shift
A change in hearing relative to the baseline audiogram of an average of 10 decibels or more at 2000, 3000 and 4000 Hz in either ear.
Temporary Threshold Shift
Fatigued Hair cells that need more energy to simulate them, reverses in 16 hrs. (OSHA 14 hrs)
PSIL (Perceived Speech Interference Level)
Average (dB) of the SPL in the Octave band center frequencies (500,1000,2000 Hz) < 60 satisfactory 60-70 difficult >70 impossible
