Noise and Vibration

Question 0

Accordingly, the Occupational Health and Safety Administration has limited permissible exposure of sound for a worker over a career to _______ dB for eight hours a day over a 40 hour work week.

Answer 0

90 dB

Question 1

The most aeromedical significant frequencies for communications are in the ________ to __________ range.

Answer 1

500 to 4,000 Hz range

Question 2

A helpful noise comparison guide for airmen is provided by the National Institute for Occupational Safety and Health: 
Whisper   30 dB
Normal conversation 60 dB
Lawn Mower     90 dB
Chain Saw   110  dB
Ambulance Siren   120 dB
Jet Engine     140 dB

NIOSH permissible exposure time limits: 
8 hours    85 dB (5 dB lower than OSHA standard)
4 hours    88 dB
2 hours    91 dB
1 hour     94 dB

Answer 2

85 dB

Question 3

Wax impregnated foam polyurethane ear plugs provide how much noise protection on average?

Answer 3

30-35 dB

Question 4

Hearing is covered under what section of FAA regulations?

Answer 4

14 Code of Federal Regulations Part 67

Question 5

The frequencies most important for human speech are:

a) 20 to 500 Hz
b) 500 to 4,000 Hz
c) 3,000 to 6,000 Hz
d) 6,000 to 20,000 Hz

Answer 5

b) 500 to 4,000 Hz

Question 6

The mechanism of the ear for converting the sound pressure waves from an air to a fluid medium without signficant loss of energy is called impedance matching and this is done through:

a) rapid fatigue of the auditory nerves.
b) movement of the otoliths in the cochlear canals
c) size differential between the eardrum and the footplate of the stapes and the lever action of the ossicles.
d) the property of binaural hearing and that sound waves do not strike the ears at the same intensity.

Answer 6

c) Only 1% of airborne sound enters the liquid medium whereas 99% is reflected away. The middle ear has two arrangements to narrow this potential energy loss. The first is the size differential between the eardrum and the footplate of the stapes. The second is the lever action of the ossicles amplifies the intensity of sound as it traverses the middle ear by 2.5 dB.

Question 7

Noise exposure is commonly thought to be a combination of time and exposure level. What is the criterion noise exposure level which would give a person a daily limiting noise exposure for an 8 hour period with the associated exchange rate according to the US military and US EPA?

a) 84 db for 8 hours with 4 db per doubling
b) 85 db for 8 hours with 3 db per doubling
c) 90 db for 8 hours with 5 db per doubling
d) 78 db for 8 hours with a 6 db per doubling

Answer 7

b) 85 db for 8 hours with 3 db per doubling

Question 8

Loudness is a psychoacoustic phenomenon. When a listener judges a sound to be twice (or half) as loud when compared to another sound, the difference is sound pressure level between the two sounds is approximately ___________.

Answer 8

10 dB

Question 9

Parameters describing an oscillatory motion are:

a) amplitude
b) frequency
c) period
d) acceleration
e) all the above

Answer 9

e) all the above

Question 10

When excited with certain input frequencies, resonances of body parts can occur, ie- the deformation or displacement of the organ is much larger at the resonance frequency than at other frequencies. The body’s lowest tolerance to vibration is:

Answer 10

4-8 Hz

Question 11

Many noise control problems require a practical knowledge of the relationship between pressure, intensity, and power. In measuring noise levels in locations that are reverberant, one can expect that the noise levels will be:

a) lower than predicted values
b) higher than predicted values
c) at the predicted values
d) none of the above

Answer 11

b) higher than predicted values

Question 12

The limiting factor for the toleration to vibrations of 2-12 Hz is:

a) Chest pain
b) Dyspnea
c) Tachyarrhythmia
d) abdominal pain

Answer 12

a) Chest pain

Question 13

A simplified model for the representation of a vibratory system is made up of:

a) a mass, a spring, and a shock absorber
b) a mass, a spring, and a damper
c) a mass, a filter, and a damper
d) a mass, a spring, a damper, and a filter

Answer 13

b) a mass, spring, and a damper

Question 14

Whole body vibration occurring in flight concerns primarily those frequencies between:

a) 20-20,000 cycles/second
b) 0.5-200 Hz
c) 0.01-1.0 Hz
d) greater than 100 cycles/second

Answer 14

b) 0.5 -200 Hz

Question 15

The effects of vibration at frequencies of less than 2 Hz include all of the following EXCEPT:

a) motion sickness
b) fatigue
c) inability to maintain control of the aircraft
d) hearing loss
e) structural aircraft damage

Answer 15

d) hearing loss

Question 16

The ordinary sound level meter:

a) gives a direct measurement of loudness
b) cannot accurately measure impulse noise
c) is capable of accurate frequency analysis
d) is the preferred instrument for detailed monitoring and specific analysis of sound content.

Answer 16

b) cannot accurately measure impulse noise

Question 17

Resonance of a system exposed to forced vibration exists when any change, however small, in the frequency of excitation causes ________________.

Answer 17

A decrease in a response of the system.

Question 18

The only specific vibration induced disease with well supported evidence is:

a) whole body vibration syndrome
b) vibration induced back pain
c) White Finger syndrome
d) retinal detachment
e) vibration induced menstrual disorder

Answer 18

c) Vibration Induced White Finger Syndrome.

Question 19

According to the vibration exposure criteria presented in ISO 2631, the seated or standing human exposure to whole body vibration in the VERTICAL direction is most sensitive to vibration frequencies occuring between ___________.

Answer 19

4-8 Hz

Question 20

According to the vibration exposure criteria presented in the ISO 2631 the seated or standing human exposed to whole body vibration in the HORIZONTAL direction (lateral, fore and aft) is most sensitive to vibration frequencies occurring between ___________.

Answer 20

1-2 Hz