PDX_28_Acoustics Part 3

Question 0

A unit of sound of sorption, 1 ft.² of 100% absorbing material is one unit

Answer 0

Sabin

Question 1

The ratio of the sound intensity absorbed by the material to the total intensity reaching the material. Varies with the frequency of sound/material

Answer 1

Coefficient of absorption (A)

Question 2

The persistence of sound in an enclosed space after the source of stopped. Continuous reflection.

Answer 2

Reverberation

Question 3

The time it takes the sound level to decrease 60 dB after the source is stopped producing sound

Answer 3

Reverberation time

Question 4

The return of soundwaves from a surface

Answer 4

Reflection

Question 5

Soundwave that is been reflected with sufficient magnitude in delay so that its heard as a sound as distinct from that transmitted directly

Answer 5

Echo

Question 6

Random distribution of sound from a surface that occurs when the surface dimension is equal to the wavelength of the sound striking it

Answer 6

Diffusion

Question 7

The bending of a soundwave around an object or through an opening

Answer 7

Diffraction

Question 8

Tendency of a system to vibrate at increasing amplitude at certain frequencies

Answer 8

Resonance

Question 9

Result of multiple reflections and enclosed space in a short period of time

Answer 9

Persistence

Question 10

Reduction of sound energy levels through the use of material that absorbs reverberant sound and block airborne sound because of their high sound transmission loss factor.
Example: acoustical panels, foam curtains, fibrous material.

Answer 10

Sound insulation

Question 11

Minimizing sounds transmission from one area of the building to another through building design.

Example: location mechanical rooms, partition detailing, using dampers/pads/insulating materials

Answer 11

Sound isolation

Question 12

Process of dissipating sound energy by converting it to heat

Answer 12

Sound absorption

Question 13

Indicates a soundwave on the opposite side of the wall

Answer 13

Wall vibration

Question 14

Room who’s boundaries absorb all of the sound

Answer 14

Free Field Road (Anechoic Room)

Question 15

Phenomenon which occurs when sounds in a room that are within a narrow band of frequencies tend to sound louder and sounds of other frequencies

Answer 15

Room resonance

Question 16

Surface area of room

x Absorptivity of surfaces

Answer 16

Sabins

Question 18

(Total surface area of Barrier or component Between rooms, S) x (Coefficient of absorption, a)

Answer 18

Acoustical Absorption A (sabins)

Question 19

(Total sabins, sound observing units, A)

/ (Total service area in the room, S)

Answer 19

Noise reduction coefficient

Question 20

0.05 (the speed of sound) x

[ (Room volume, V)
/ (total acoustical absorption at that frequency, ∑A) ]

Answer 20

Reverberation time (Tr)

*speed of sound depends on material

Question 21

Low-frequency control usually requires allowance for:

Answer 21

Thicker partitions or more space to apply detailing that absorbs low-frequency sounds.

Question 22

A sized furred panel @ certain distance from wall to absorb low-frequency energy + reflecting mid & high frequency energy:

Answer 22

Panel Resonator

Question 23

A large airspace filled with absorptive material and a sized small opening to absorb specific low frequency range:

Answer 23

Cavity resonators (Helmholtz)

Ex. A CMU block, with narrow slit opening into the cavity of block

Question 24

Tipping point of reflective and absorptive in regards to ‘coefficient of absorbency’ occurs @ value:

Answer 24

0.2

Less is reflective.
More is absorbing.

Question 25

Changing room reverberation characteristics WITHIN the room effects noise level in adjoining spaces:

Answer 25

Minimally effect on adjoining spaces

Question 26

Absorptive materials are usually better at reducing the transmission of:

Answer 26

High frequencies better than low frequencies

Question 27

The effectiveness of absorptive materials dependents on:

Answer 27

The type of material, the method of installation, the area, rather than the thickness

Question 28

The absorptivity per sqft of given surface varies 0 to 1:

Answer 28

0. 0, all sound reflected

1. 0 Sabin, all sound absorbed

Question 28

Offices might have reverberation times between

Answer 28

0.3–0.6 seconds

Question 29

Very reverberant spaces often called:

Spaces with short reverberation times called:

Answer 29

‘Live’ = long reverberation

‘Dead’ = short reverberation

Question 30

Concert halls might have recommended reverberation times between:

Answer 30

1.6–2.1 seconds

Question 31

Two measures intended only for open office situations where speech is the primary sound concern:

Answer 31

Articulation class (AC)
Articulation index (AI)

Question 32

Gives a rating of system component performance does not account for masking sound

Answer 32

Articulation class (AC)

Question 34

Measure the performance of all the elements of a particular configuration working together:

Answer 34

articulation index (AI)

Ceiling absorption, wall partitions, space dividers, background masking systems, furniture, HVAC systems, light fixtures

Question 35

Critics the intelligibility of speech for a group of talkers and listeners and gives a result in a single number rating:

Answer 35

Articulation index (Ai)

Ranges from 0.00, complete privacy

To 1.00, no privacy

Question 36

Ai 0.30 =

Answer 36

No privacy

Question 36

Each doubling of the amount of absorption in a room results in:

Answer 36

Noise reduction of only 3 dB

Reduced reverberation time by 50%

Question 37

The average absorption coefficient for a room should be at least:

Answer 37

0.2

Typically above 0.5 is not desirable or economically justified.

Question 38

The amount of absorption of a porous type of sound absorber (EX: fiberglass, mineral wool) is dependent on:

Answer 38

Material thickness, density, porosity and orientation of fibers

Question 39

Ceiling treatments are best for ___,

Wa treatments are best for____.

Answer 39

Ceiling treatments @ large rooms

Wall treatments @ small rooms

Question 41

To reduce mechanical noise from vibrating device in direct contact with structure:

Answer 41

– Resilient mountings & flexible bellows
– Flex connections between ducts/pipes/equipment
– Maximize distance between diffusers in adjacent spaces
–locate noisy equipment away from quiet spaces

Question 42

To limit noise at plumbing systems:

Answer 42

– Use expansion valves & FlexLoop connections to reduce rattle
– Seal pipe penetrations through walls & floors w/ flexible packing

Question 43

Limit noise with building materials by:

Answer 43

– Use fibrous materials
– Deep air space w/in wall cavity
– Stagger studs
– Seal openings in wall
– Avoid back/back wall outlets
– Sound attenuation above headers