Acoustics

Question 1

The Boston symphony hall was acoustically designed by _______

Answer 1

Wallace Sabine

Question 2

DEF: antinode

Answer 2

the point where the amplitude of a standing wave is at is maximum

Question 3

DEF: node

Answer 3

point of no vibration, essentially the zero crossing of a waveform

Question 4

DEF: mode

Answer 4

a room resonance, a standing wave

Question 5

DEF: axial modes

Answer 5

a resonance between two room parallel surfaces (one pair)

Question 6

DEF: tangential modes

Answer 6

a resonance between four room surfaces (two pairs)

Question 7

DEF: oblique modes

Answer 7

a resonance between all six room surfaces (3 pairs)

Question 8

The Schroeder Frequency of a room determines:

Answer 8

the point at which resonances become less problematic reflections

Question 9

Reduction of reflections to an imperceptible loudness is called:

Answer 9

RT60

Question 10

DEF: RT60

Answer 10

The time requird for the sound in an enclosure to decay 60 dB from an initial steady-state level

Question 11

An absorption coefficient of 0 equals:

Answer 11

total reflection

Question 12

In order to take an impuse response a room may be excited by ________

Answer 12

a sine sweep or a loud click (ie. gunshot)

Question 13

In order to catch a wavefront at maximum velocity an absorber must be equal to what fraction of a wavelength?

Answer 13

1/4 wavelength

Question 14

How does an air cavity between an absorber and a boundary affect its acoustic performance?

Answer 14

It increased the performance at lower frequencies

Question 15

Describe a Tom Hidley control room design

Answer 15

a reflective front wall

Question 16

In a control room do you want parallel or non-parallel surfaces?

Answer 16

Non parallel

Question 17

What is the Sabine Equation?

Answer 17

Question 18

What do we use Sabine’s equation to calculate?

Answer 18

reverb time

Question 19

Identify the type of control room design

Answer 19

a Tom Hidley design

Question 20

How does thickness of a material affect it’s absorption coefficient at lower frequencies?

Answer 20

thicker abosrbes more of lower frequencies as they have larger physical soundwaves

Question 21

DEF:

absorption

Answer 21

When sound energy is converted into heat energy as it passes through a medium

Question 22

how can you increase diffusion?

Answer 22

• non parallel surfaces
• use of geometric irregularities
• use of concave surfaces or diffusion panels
• use of every day objects (ie. book cases)

Question 23

name this diffuser

Answer 23

MLS ( Maximum length sequence) Diffuser

Question 24

DEF:

room mode

Answer 24

the normal modes of vibration in an enclosed space

Question 25

name this diffuser

Answer 25

skyline diffuser

Question 26

name this diffuser

Answer 26

QRD (Quadratic Residue Diffuser)

Question 27

name this diffusor

Answer 27

Schroeder's Diffusor

Question 28

What constitutes a perfectly diffuser environment?

Answer 28

- no measured frequency or level irregulariries - smooth reverberation decay - same rever decay for all frequencies and from all directions - same reverb time at all points in the room

Question 29

name this acoustic treatment

Answer 29

bass trap

Question 30

name this acoustic treatment

Answer 30

perforated panel absorbers

Question 31

name this acoustic treatment

Answer 31

Helmholtz Resonator

Question 32

name this acoustic treatment

Answer 32

Helmholtz Resonator

Question 33

What equation is used to calculate the maximum frequency that can be absorbed by a substance?

Answer 33

Question 34

with porous absorbers, what dictates the degree of absorption?

Answer 34

the space between the fibres if fibres are not packed closely enough, little energy will be lost as heat if fibres are packed too closely, sound may not penetrate absorber sufficiently

Question 35

name this acoustic treatment

Answer 35

porous absorbers

Question 36

DEF: acoustic absorption

Answer 36

the process by which a medium takes in sound energy as opposed to reflecting it. Part of the absorbed energy is transformed into heat and part is transmitted through the absorbing body

Question 37

What word do we use to discribe the sound energy that has been converted to heat via acoustic absorption

Answer 37

energy transformed into heat is said to have been 'lost'

Question 38

Who developed the quadratic residue diffuer (QRD)?

Answer 38

Manfred R. Schroeder

Question 39

In a QRD the well depth dictates \_\_\_\_\_\_\_

Answer 39

the lowest frequency for diffusion

Question 40

In a QRD the well width dictates the \_\_\_\_\_\_\_\_

Answer 40

highest frequency for diffusion

Question 41

what equation is used to calculate the well depth sequence in a QRD?

Answer 41

Question 42

what does the 'modulo' refer to?

Answer 42

the remainder

Question 43

What is the use of a Helmholtz resonator?

Answer 43

used to achieve absorption at lower frequencies

Question 44

DEF: STC

Answer 44

Sound Transmission Class a single number used to describe a series of transmission loss measurements made at frequency intervals throughout the frequency range. A standardised class system based on how well a medium attenuates sound.

Question 45

what does MLS stand for?

Answer 45

Maximum length sequence

Question 46

What are the three godlen room ratios?

Answer 46

Question 47

What equation is used to calculate a room mode?

Answer 47

Question 48

What equation is used to calculate the Schroeder frequency?

Answer 48

Question 49

What equation do you use to calculate standing waves?

Answer 49

Question 50

DEF: standing wave

Answer 50

a resonance condition in an enclosed space in which sound waves travelling in one direction interact with those travelling in the opposite direction , resulting in a stable condition

Question 51

DEF: reflection

Answer 51

sound is reflected much like light, with the angle of incidence equaling the angle of reflection

Question 52

DEF: Helmholtz resonator

Answer 52

a reactive, tuned sound absorber