Chapter 20 Noise and vibrations in Mechanical and Electrical Systems
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) Which of the following are commonly required in general office space? Select all that apply. 1) _______
A) Reverberation control. B) Reasonable control of mechanical noise.
C) Speech intelligibility. D) Soundproof walls.
2) Which of the following are commonly required in executive conference rooms? Select all that
apply.
2) _______
A) Speech intelligibility. B) Reverberation control.
C) Soundproof walls. D) Reasonable control of mechanical noise.
3) The reference pressure fluctuation used in calculating decibel ratings is which of the following? 3) _______
A) The optimal level of hearing sensitivity.
B) The threshold of audibility.
C) The inverse of the threshold of pain.
4) What are the low and high centers of frequencies of octave bands most common in engineering? 4) _______
A) 125 to 4000. B) 62.5 to 8000. C) 31.3 to 8000.
5) What is the relationship of two frequencies which are an octave band apart? 5) _______
A) The higher frequency is 6x the lower.
B) The higher frequency is 2x the lower.
C) The higher frequency is 8x the lower.
6) Overall sound levels are commonly reported as dBA. What is the significance of this value? 6) _______
A) Reports octave band readings as they are measured, without adjustment.
B) Adjusts sound measurement more to resemble the response of the ear at much higher
levels.
C) Adjusts sound measurement to approximate the response of the ear at modest sound
levels.
7) The human ear is most sensitive to sounds at which of the following frequencies? 7) _______
A) 63 Hz. B) 1000 Hz. C) 500 Hz. D) 250 Hz.
8) Which of the following is true? Select all that apply. 8) _______
A) A 3-dB change in sound pressure level is barely perceptible.
B) A 1-dB change in sound pressure level generally goes unnoticed.
C) A 6-dB increase in sound pressure level is generally perceived as twice as loud.
9) Which of the following is most effective at absorbing low frequency sound? 9) _______
A) Concrete.
B) Porous materials.
C) Single layer gypsum panels.
10) How is the quantity “noise criteria“, or NC, used? 10)
______
A) To assess the background noise in a space.
B) To quantify the dbA in a space from a piece of equipment.
C) To measure the frequency distribution of noise in a space.
11) For speech intelligibility in spaces where this is a primary requirement–churches, auditoriums, etc. –the
backgrou
nd
sound
level
should
be at
least
how
many dB
below
the voice
level?
11) ___
___
A) 15 dB. B) 5 dB. C) 10 dB.
12) How would you design to avoid duct noise from above the ceiling? Select all that apply. 12)
______
A) Increase aspect ratio to achieve larger duct absorption surface.
B) Avoid sharp, abrupt edges at takeoffs.
C) Install sound traps at the beginning of the supply main.
D) Restrict velocities to 3000 fpm maximum.
13) Which of the following will be effective in reducing low frequency noise from a mechanical
room?
13)
______
A) Sound batts in the stud space.
B) Mounting the drywall on resilient channels.
C) Acoustical liner on the walls.
14) What would be the effects of elevating a rooftop unit above the roof? Select all that apply. 14)
______
A) Breakout noise from the casing would be increased by eliminating the curb.
B) Air noise would increase due to extra ductwork to get from unit to roof.
C) Decoupling it from the roof would reduce transmission of vibration.
15) Which of the following values would be the best ratio of the forcing frequency to the natural
frequency of a vibration base design?
15)
______
A) 2.0. B) 1.0. C) 3.0.
16) What’s a good rule of thumb for sizing an inertia base? 16)
______
A) At least 2x the weight of the equipment.
B) About 1/2 the weight of the equipment.
C) Equal to the weight of the equipment.
17) What is the purpose of a snubber in a seismic design? 17)
______
A) To minimize vibration by constant contact.
B) To stop the equipment as it hits the snubber.
C) To hold the equipment in place tightly and prevent movement.
