ERGONOMICS - Hearing (auditory sense)

Hearing as an auditory sense.

1. HEARING

2. Acoustics The science and technology of sound, including its production, transmission, and effects

3. T ransmit desired sounds reliably and pleasantly to the hearer S atisfactory to the human regarding noise Minimizes sound-related annoyance and stress Minimizes disruptions of speech P revents hearing loss Acoustical design goal

4. Psycho-Acoustics Describe how we perceive sound in relation to their physical properties (pitch , timbre, loudness, noise and speech comprehension)

5. SOUND Any vibration (passage of zones of compression and rarefaction through the air or any other physical medium) that stimulates an auditory sensation .

6. Ear Anatomy and Hearing

7. HOW DO WE HEAR?

8. A single-frequency oscillation , while a sound contains a mixture of frequencies The frequencies (frequency distributions) are measured in hertz (Hz ) . The intensities (amplitude and sound pressure levels) in logarithmic units known as decibels (dB ) . TONE The human HEARING range

9. can rarely hear frequencies above 12 kHz ADULT can hear tones of about 16 Hz to 20 kHz YOUNG The minimal pressure threshold of hearing is about (or 20 micropascals ; ) in the frequency range of 1,000 to 5,000 Hz  

10. RANGES OF ADULT HUMAN HEARING

11. Sound Pressure Level or   Where: P ₒ = the threshold of the hearing P = root-mean-square ( rms ) sound pressure for the existing sound Sound Intensity Level   Where: I ₀ = I = root-mean-square ( rms ) sound intensity  

12. SOUND INTENSITY LEVELS

13. Airborne sound travels through the ear canal and excites the eardrums and the structures behind it Sound may also be transmitted through the bony structures to the head and ear The velocity V of sound in solids, liquids, and gases is determined by the modulus of Elasticity E of medium and its density D Where: E = N/ Pa D = kg/   Pathways of Sound

14. Fox (1983) distinguished between two different kinds of music : background and industrial. Background Music is like “acoustical wallpaper” in shops, hotels, waiting rooms, etc. Such music is meant to create a welcoming atmosphere, to relax costumers, to reduce boredom, and to cover other disturbing sounds . Its character is subdued, its tempo intermediate, and vocals are avoided. Industrial Music or “Music while you work ” is not continuous, but programmed to appear at certain times. It has varying rhythms with vocals, and it may contain popular “hits.” Human Responses to Music

15. “White” noise has equal power per hertz throughout all frequencies. It sounds like electronic static . “Pink” noise has power per hertz which decreases as the frequency increases. It sounds more like a waterfall S ound that is unwanted, objectionable, annoying, or unacceptable to a person, which is often but not always loud NOISE

16. Noise can create negative emotions, feelings of surprise, frustration, anger, and fear Noise can delay the onset of sleep, awaken a person from sleep, or disturb someone’s rest; Noise can make it difficult to hear desirable sounds Noise can produce temporary or permanent alterations in body chemistry Noise can temporarily or permanently, change one’s hearing capability Noise can interfere with some human sensory and perceptual capabilities and thereby degrade the performance of a task HUMAN RESPONSE TO NOISE

17. The damage is probably due to an overstimulation of cell metabolism, leading to oxygen depletion and destruction, or to exceeding the elastic capacities of the physical structures. R esults of damage to the cochlear cilia, the organs of Corti at the basilar membrane in the inner ear, or the nerves leading to the CNS. Temporary Threshold Shift (TTS ) and Permanent Threshold Shift (PTS) The muscles of the middle ear contract, mostly affecting the stapes and thereby reducing the transmission of force to the cochlea Abnormal heart rhythms have been associated with exposure to noise The concentration of corticosteroids in the blood and the brain is increased and the also affects the size of the adrenal cortex. Electrolytes in the body become imbalanced, and the blood glucose levels change. Sex hormone secretion and thyroid activity may also be affected by noise. Physiological Effects of Sound Other physiological effects

18. PHYSIOLOGICAL EFFECTS OF NOISE

19. A permanent hearing impairment resulting from prolonged exposure to high levels of noise It can be caused by a one-time exposure to an intense “impulse” sound, such as an explosion, or by continuous exposure to loud sounds over an extended period of time, such as noise generated in a woodworking shop Recreational activities that can put you at risk for NIHL include target shooting and hunting, snowmobile riding, listening to MP3 players at high volume through ear buds or headphones, playing in a band, and attending loud concerts Harmful noises at home may come from sources including lawnmowers, leaf blowers, and woodworking tools Noise-induced Hearing \ Loss ( NIHL ) ) What causes NIHL?

20. Psychological effects of noise include anxiety, helplessness, narrowed attention, and other adverse effects that degrade task performance. As noise becomes more intense, we become more aroused and our performance of certain tasks can improve. Beyond a certain level of intensity, however, task performance degrades. Sudden, unexpected noise can produce a startle response that interrupts one’s concentration and physical performance of a task. Continuous periodic or aperiodic noise interferences with the performance of complex tasks, such as visual tracking: performance is diminished with increasing noise levels. EFFECTS OF NOISE

21. EFFECTS OF NOISE ON HUMAN PERFORMANCE

22. Three Strategies to PREVENT NIHL Impede the transmission of sound from the source to the listener A void the generation of sound by properly designing machine parts such as gears or bearings, reducing rotational velocities, changing the flow of air, or replacing a noisy apparatus with a quieter one R emove humans from noisy places altogether, at least for parts of the work shift

23. HEARING PROTECTION DEVICES An earplug is a device worn in the external ear canal which is commonly made from vinyl, silicone, elastomer formulations, cotton and wax, spun glass wool, and slow-recovery closed-cell foam A semi-insert earplug , also called an ear-canal cap. This sort of device is held in place by a lightweight headband with mild tension . An earmuff is a device composed of a headband and two circumaural cups that are usually made of plastic