• Pinna or auricle – external part

• Ear proper is divided into three parts : outer, middle and inner ear

•Ear canal and terminates at the ear drum (tympanum)

•Pressure variations in sound waves exert forces on the ear drum and cause it to vibrate.

•Hammer, Anvil and Stirrup (malleus, incus and stapes) – three small bones.

•Cochlea – converts sound waves into nerve signals.

• Sound waves ENTERS

PRESSURE

VIBRATIONS

HAMMER

ANVILSTIRRUP

OVAL WINDOW

Fluid Hair CellsHair CellsElectrical impulse

Auditory nerveBRAINBRAIN

•Awareness through the senses.

•The human ear has a remarkable sensitivity and range.

•It can detect sounds varying in intensity by a factor of 10^12.

•Frequency :

20-20,000 Hz (Hertz)

• is the perception of frequency.

•Frequencies usually must differ by 0.3% or more to be told apart.

•Example, 1000 and 1003 Hz are noticeably different in pitch.

•A person with a poor sense of pitch.

•Multiple frequency sounds are often perceived subjectively. A number of terms are used to describe multiple-frequency sounds such as:

•*Noise *Rich *Mellow•*Music *Shrill

•Most music utilizes frequencies whose ratio are integers/ simple fractions.

•Humans are able to recognize individual frequencies played simultaneously even though the combined sounds may be complicated in appearance.

•Is the perception of intensity, a well-defined physically measurable quantity.

•At a given frequency the more intense a sound is, the louder it seems. The ear does not respond linearly to intensity; a sound ten times as intense as another does not sound ten times as loud.

•Are physically measurable and are fairly representative of the comparative numbers that people would assign to the loudness of sounds.

•The smallest difference in intensity an average person can sense is about 1 dB, and an intensity difference of 3 dB is easily discernable.

•Loudness depends strongly on frequency as well as intensity. Two sounds of different frequencies but equal intensities rarely sound equally loud. This is because the ear is more sensitive to some frequencies than others.

•Vey large intensities are needed for sound audible near the extremes of the normal range of hearing- approximately 100 dB at 20 or 20,000 Hz, for example.

•The threshold for normal hearing is often defined as 0 dB at 1000 Hz, corresponding to 10^-12 W/m^2 (Iₒ in definition of decibels).

• One cause of the sensitivity of the ear to the frequencies in the 2000-5000-Hz range is resonance of air in the outer ear. The length of the ear canal is such that sounds of about 3000 Hz will cause the air in it to resonate, amplifying the sound and making the air more sensitive to frequencies around 3000 Hz.

• Perception of loudness depends on frequency as well as intensity.

• Loudness is at least as important as intensity.

• Loud sounds can be very irritating, to the point of increasing blood pressure. It is important to keep the sound level low in hospitals, for example, but it is not important to reduce the intensity of all frequencies by the same amount.

•Unit for loudness.•Phons and decibels are said to be the same at 1000 Hz. A 60-dB 1000 Hz sound has a loudness of 60 phons, for example.

•At high intensities the ear responds equally well to most frequencies, although it remains more sensitive in the region around 3000 Hz. For example a 100 dB 60 Hz sound and a 100 dB 800 Hz sound are both of equal loudness.

•Sound-level meters•Are designed to measure sound levels as humans would respond to them; their output is representative of loudness rather than intensity.

•The three internationally accepted weightings given to sounds in sound level measurements are…

• The A weighting makes the meter respond most like the ear at low intensities since it suppresses the response to low frequencies.

• The B and C weightings are more representative of the response of the ear to moderate and high intensities, with the C weighting being nearly equal at all frequencies.

•3 aspects1. Distance from a source2. Attenuation by absorption3. Reduction of sound output

from the source (most effective)

• The smaller the area of the object, the less air it can interact with and the lower level it will create. The more rigid the materials of which the vibrating object is made, the smaller amplitude its surface will have, producing smaller pressure waves in the air. The vibrating object should be cushioned from contact with other objects it might cause to resonate.

•Perception is traditionally the domain of disciplines other than physics. Knowledge of sound perception aids greatly in treating hearing loss, designing musical instruments and reducing noise.

•Age (most common)•Trauma (sudden injury)•Prolonged exposure to high sound levels

•Disease•Congenital birth defects

•Caused by defects in the structures that conduct sound to the inner ear

• Also called sensorineural, for sensory and neural

• Results from damage to the cochlea or neurons that send sound information to the brain.

• Like any nerve damage, it is generally difficult to correct.

•One step in evaluating hearing loss is to administer hearing tests. These tests not only determine the severity of a hearing loss but also aid in determining its type and correctability.

•The most common testing procedure is to place the patient in a soundproof room and ask him/ her to signal when a sound becomes audible. The intensity of sound is raised and lowered to determine the threshold of hearing for that person. Each ear is tested individually, usually using a headset.

• Using a bone conduction of sound rather than normal air conduction. In bone conduction tests a probe is placed against the skull behind the ear and sound vibrations of various frequencies and intensities are sent to the inner ear.

•Bone conduction tests bypass the outer and middle ear structures; if hearing is significantly better by bone conduction, then the hearing loss is conductive rather than neural.

• A graph of the results of a hearing test. The hearing threshold levels graphed on the vertical axis are the number of decibels above the normal threshold needed to be barely audible to the person tested ( A person with normal hearing will have a test result of 0 dB at every frequency)

• Attenuation of sound in bone varies with frequency and differs with from attenuation in air.

• At high intensities, bone conduction carries the sound to both ears, and the testing device may make significant air noises.

•Most of these difficulties are overcome by careful and consistent technique and by putting noise into the ear that is not being tested, this is called masking.

• Air conduction tests are more accurate because air attenuation is negligible for all frequencies and the equipment can be calibrated more easily. Sound conduction by air into one ear is attenuated by about 50 dB before it gets o the other ear, so there is little confusion as to which ear is responding.

•A 45-year old person usually has a 10 dB loss and cannot hear frequencies over 12,000 Hz at all. A person 65-years old typically has a 30 dB loss for frequencies above 3000 Hz.

• Conduction failures affect more than just a narrow range of frequencies. Bone conduction tests are considered unnecessary for such conditions. The loss is not easily treatable, because sound amplification at one frequency is not easy in a device as small as a hearing aid, and neural damage cannot be repaired surgically.