HEARING

AcousticsThe science and

technology of sound, including its production,

transmission, and effects

• Transmit desired sounds reliably and pleasantly to the hearer

• Satisfactory to the human regarding noise

• Minimizes sound-related annoyance and stress

• Minimizes disruptions of speech

• Prevents hearing loss

Acoustical design goal

Psycho-AcousticsDescribe how we perceive sound in relation to their

physical properties (pitch, timbre,

loudness, noise and speech

comprehension)

SOUNDAny vibration (passage of zones of compression and rarefaction through

the air or any other physical medium) that stimulates an auditory

sensation.

Ear Anatomy and Hearing

HOW DO WE HEAR?

The human HEARING range

can rarely hear frequencies

above 12 kHz

ADULTcan hear tones

of about 16 Hz to 20 kHz

YOUNG

RANGES OF ADULT HUMAN HEARING

Sound Pressure Level

or

Where:

Pₒ = the threshold of the hearing

P = root-mean-square (rms) sound pressure for the existing sound

SOUND INTENSITY LEVELS

Airborne sound travels through the

ear canal and excites the eardrums and

the structures behind it

Pathways of Sound

Fox (1983) distinguished between two different

kinds of music: background and

industrial.

Human Responses to Music

Sound that is unwanted, objectionable, annoying,

or unacceptable to a person, which is often but not always loud

NOISE

Noise can create negative emotions, feelings of surprise, frustration, anger,

and fear

HUMAN RESPONSE TO NOISE

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.

Results 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)

Physiological Effects of Sound

PHYSIOLOGICAL EFFECTS OF NOISE

A permanent hearing impairment resulting

from prolonged exposure to high levels

of noise

Noise-induced Hearing

\Loss (NIHL))

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.

EFFECTS OF NOISE

EFFECTS OF NOISE ON HUMAN PERFORMANCE

Three Strategies

to PREVENT

NIHL

Avoid 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

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