ar2ae045-ra1 room acoustics 1

ROOM ACOUSTICS ROOM ACOUSTICS ROOM ACOUSTICS ROOM

Acoustics

Room AcousticsRoom Acoustics

Lecture AR2AE045-D1-1

Martin Tenpierikp

DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 1


Introduction Architectural Acoustics can be subdivided into

Room Acoustics / Spatial Acoustics

Traffic Noise and Urban Acoustics

Sound Insulation and Sound Proofing



Content This lecture focuses on Room Acoustics.

Room Acoustics includes acoustics of concert halls, theaters and auditoria.

But also:- Noise reduction in noisy spaces- Speech intelligibility in rooms / offices / schoolsSpeech intelligibility in rooms / offices / schools- Sound propagation through “Coupled Rooms”

Concert halls only once per 10 year ??Restaurant nearly every day



Room Acoustics

Sound Reflection in EnclosuresSound Reflection in Enclosures



Thousands of Rays!

longer path

later arrival

“reverberation"

direct sound

microphone



Measuring a Room

Past:- Use alarm pistol or clap your hands: “impulse”And listen or register on tapeAnd listen or register on tape

Nowadays:Use loudspeaker and microphone- Use loudspeaker and microphoneCalculate impulse response on computer

Different signals can be used:Different signals can be used:- Digital noise (white noise, pink noise)- Sweep signals



Impulse Response

An Example direct

echoecho reverberation

100 ms time axis00 s time axis



Our Ears + Brains

They are sensitive to Energy or Power

And are a logarithmic ‘device’And are a logarithmic device



Energy ~Pressure SquaredSquared

linear

direct

scale

0.3 stime axis

echo

time axis



Echogram

direct

echolog-

scale

0.6 stime axis

20 dB

time axis



Often drawn as

80direct

ude

[dB

]“reverberation"

60

Am

plitu

400 0 0 1 0 2 0 3 0 40.0 0.1 0.2 0.3 0.4

time [s]



Backward Integration:

Schröder

1 stime

20 dB

time



Reverberation Time:

Sabine’s Definition (1900)

reverberation time T

(1900) 60 dB decreasedraw straight line

1 stimetime



Example: Reverberation time

Reverberation in a room

T = 0 6 s in a small roomtime T = 0.6 s in a small room

T = 1.0 s in a small room

T = 2.0 s in a big room

T = 2.5 s in a big room



Reverberation Time:

From the energy balance of a room, Sabine derived an equation for the reverberation time as:

Sabine’s Definition (1900) 0

55.3 0.1616

V V VTc A A A

(1900)

c0 = speed of sound wave in air (=340 m/s)

l f ( 3)V = volume of room (m3)A = total absorption in room (m2 sabin) = sound absorption coefficient of a surface (-)1

n

i ii

Sp ( )

S = area of a surface (m2)

This equation can be derived from the energy balance of the


This equation can be derived from the energy balance of the room in case of a diffuse sound field.


Reverberation Time:

Energy balance equation of a room:

dEW V IA Derivation

W = power of sound source (W)

W V IAdt

V = volume of room (m3)E = energy density in room (J/m3)t ti ( )t = time (s)I = acoustic intensity in room (W/m2)A = total absorption in room (m2 Sabine)A total absorption in room (m Sabine)



Reverberation Time:

Reverberation time is the decay of acoustic energy after a source is switched off (thus W =0 W):

dDerivation 0 dEV IAdt

Since and in a diffuse field,2

2effp

Ec

2

4effp

Ic

the equation becomes

0c 04 c

22 0( )

( )4

effeff

dp t c Ap tdt V



Reverberation Time:

Assuming p2eff(t) = p2

eff(0) at t = 0, the solution to this equation becomes

Derivation 02 2 4( ) (0)

c AtV

eff effp t p e

or024

2

( )10 log 10log

(0)

c Ateff Vp t

e

which equals

2g g(0)effp

02 24

2 20 0

(0) ( )10log 10log 10log

c Ateff eff Vp p t

ep p


0 0


Reverberation Time:

Since T is defined for a decay of 60 dB, the term on the left hand side of the equation is 60 dB

Derivation 0460 10logc AT

Ve

or

6 55.3 55.34ln 10 V V VT 0 0 0

4 ln 10

tot

Tc A c A c S



Reverberation Time:

Sabine’s definition however gives problems for high average absorption coefficient. Eyring therefore derived another reverberation time as:

Eyring’s Definition (1930)

derived another reverberation time as:

55.3

V VT(1930)

d f d i i ( 340 / )

0 ln 1 6 ln 1 tot totc S S

c0 = speed of sound wave in air (=340 m/s)

V = volume of room (m3)Stot = total surface area in room (m2)Stot o a su ace a ea oo ( ) = average absorption coefficient (-)

Th d i i ill b d h


The derivation will not be presented here.


Reverberation Time

Sabine versus Eyring

55 3 VSabine:

55 3 V0

55.3

tot

VTc S

Eyring: 0

55.3ln 1

tot

VTc S

- Note the minus sign in Eyring’s equation

- Differences are small if is small

- Differences become bigger if approaches 1


gg pp


Reverberation Time:

Sabine’s and Eyring’s reverberation time:

Example Room size: 13 x 10 x 6 m3

Average sound absorption coefficient: 0.21

Total Absorption: 0.21 x 536 = 113 m2 sabin

55 3 78055.3 780 1.1340 0.21 536sabT s

55.3 780 1.0340 536 ln(1 0.21)eyrT s



4

Sabine vs.Eyring

A room with V/Stot = 3 m

2 5

3

3,5m

e, T

[s]

1,5

2

2,5

rber

atio

n tim

0

0,5

1

Reve

r

SabineEyring

00 0,2 0,4 0,6 0,8 1

average absorption coefficient [-]



Reverberation Time:

60 dB??

Extrapolation only allowed if

1 stime

y

straight line!

time



Reverberation Time:

Sometimes therefore other intervals are used for characterising a room:

T i t l f 30 dBOther definitions

- T30 uses an interval of 30 dB multiply the found value with 2

- T15 uses an interval of 15 dB 15

multiply the found value with 4- EDT (Early Decay Time) uses the first 10 dB decay

multiply the found value with 6multiply the found value with 6



Reverberation Time

T is often used as a measure for acoustical quality

- 1.5 - 2.2 s for music- 0.8 - 1.0 s for speech- 0.8 s for an office (too high ??)( g )- 0.4 - 1.2 s in dwellings- 0.3 - 0.4 s maximum for the ‘hearing impaired’- 0.1 - 0.2 s is often disliked



Reverberation Time

Problem however is that T depends on volume:

- 0.4 s for a living room

- is 1.8 s for a sports facility if scaled-up

Therefore a better measure is needed:Therefore a better measure is needed:- STI (Speech Transmission Index): from 0 to 1;- C50 , U50 (clarity): from -15 dB to +15 dB;- average (average absorption coefficient): 0 to 1

ll l dStill, T is most commonly used.



Room Acoustics

Influence of Sound Absorbing MaterialsInfluence of Sound Absorbing Materials


ROOM ACOUSTICS ROOM ACOUSTICS ROOM ACOUSTICS ROOMabsorbed + transmitted

Absorbing Surface absorbing material

sound sound

microphone



Increasing Absorption

80 Multiple reflections:Direct sound not affected

Decrease of reverberation time ud

e [d

B]

Multiple reflections:

extra energy loss

time60

Am

plitu

400 0 0 1 0 2 0 3 0 40.0 0.1 0.2 0.3 0.4

time [s]



Speech Intelligibility and Musical Clarity 80Musical Clarity

Boundary:50 ms: Speech ud

e [d

B]

50 ms: Speech80 ms: Music 60

Am

plitu

400 0 0 1 0 2 0 3 0 40.0 0.1 0.2 0.3 0.4

time [s]

early: energy increase late: disturbing noise



Increasing Absorption

80However, total energy

ude

[dB

] Is reduced

60

Am

plitu

400 0 0 1 0 2 0 3 0 4

Ratio of early to late increases

0.0 0.1 0.2 0.3 0.4time [s]

early: energy increase late: disturbing noise



Reverberation Time Revisited

Should we choose reverberation time as low as possible?

Revisited

Yes, reverberation decreases speech intelligibility

Maybe, but sound pressure level might get too low

No, people do not like anechoic music



Reverberation Time Revisited

Yes Maybe or No

RevisitedAcoustic design is a compromise!

E.g., a theatre is not the same as a concert hall.



Room Acoustics

Absorption MechanismAbsorption Mechanism



Types of Absorption

Three types of sound absorption are distinguished:

- Friction of molecules in porous material;

- Panel resonance (mass-spring system)

- Perforated panels: Helmholtz resonance + panel resonance



Types of Absorption:

transmissionFriction of Molecules

transmission

absorption

reflectionincident

abs. + transm. + refl. = incident




Hole size (or specific flow resistance) is essential.

Friction of Molecules

Too open hardly any friction

OKOK

Too dense hardly any entrance




Reflection at back wall reduces absorption…


reflection at backsiderigid layer, like concrete

absorption material

reflectionincident reflectionincident

… but mostly needed as structure and for reducing


y gsound transmission.



Absorption as a function of frequency

1.0laagdikte 4 cmLayer thickness 4 cm


0 6

0.8ci

ent

g20 000 Ns/m4

Layer thickness 4 cmFlow resistance 20000 Ns/m4

0.4

0.6

sorp

tieco

effic

harmonics

0 0

0.2

abs

fundametalsspeech

harmonics

speech

0.050 100 200 400 800 1600 3150

frekwentie [Hz]



1.0stromingsweerstand 20 000 Ns/m4


Thickness of absorption layer is important as well

Flow resistance 20000 Ns/m4

0 6

0.8ci

ent

16


Flow resistance 20000 Ns/m

0.4

0.6

sorp

tieco

effic

laagdikte 1 cm24

8

Layer thickness 1 cm

0 0

0.2

abs

Acoustic wall paper does not exist

Carpet needs to be thick

0.050 100 200 400 800 1600 3150

frekwentie [Hz]Modern plaster ??




Paint layers or thin protective films cause shielding of the material from acoustic waves above the following frequency:

Panel Resonance

following frequency:

0 0 4102 2shield

cft t

th ifi ti i d (k / 2/ )

2 2f f f ft t

0c0 the specific acoustic impedance (kg/m2/s)

ftf the mass of the film (kg/m2)




Absorption due to resonance of mass-spring system.

Panel Resonance

rigid layer, like concrete

thin panel(filled) cavitySPRING

MASS

reflectionincident




Absorption highest near resonance frequency:

'1 60sPanel Resonance

1 602 0.6

tres

plate cav

sfm m a b d

with m the mass of the system (kg/m2)

mplate the mass of the plate (kg/m2)

s’t the stiffness of the spring (air layer) (N/m3)

dcav the thickness of the cavity (m)

a, b the dimensions of the plate (m)





1.0laagdikte 4 cm

Panel Resonance

0 6

0.8ci

ent

g20 000 Ns/m4

0.4

0.6

sorp

tieco

effic

0 0

0.2

abs

0.050 100 200 400 800 1600 3150

frekwentie [Hz]




Absorption due to resonance of mass-spring system.

Perforated Panels

rigid layer, like concrete

perforated panelporous absorber

reflectionincident




Absorption highest near:

ePerforated Panels

54resplate cav

efd d

with e the degree of perforation (-)

dcav the thickness of the cavity (m)

dplate the thickness of the perforated plate (m)

e should be smaller than 30%





1.0laagdikte 4 cm

Perforated Panels

0 6

0.8ci

ent

g20 000 Ns/m4

0.4

0.6

sorp

tieco

effic

0 0

0.2

abs

0.050 100 200 400 800 1600 3150

frekwentie [Hz]



Room Acoustics

Some Examples of Absorption MaterialsSome Examples of Absorption Materials



Examples of Absorbers:

Standard Office


© Lau Nijs



Integrated Ceiling


© Lau Nijs



Absorbing Plasters


© Lau Nijs



Perforated Panels


© Lau Nijs



Carpets


© Lau Nijs



Panels


© D. Bankersen en L.M. Schaberg



Plants??

Yes but youYes, but you need a lot of them


© Roby van Praag



Baffles


© Lau Nijs


Room Acoustics

Sound Power LevelSound Power Level

Sound Pressure Level



Recapitulation from Previous Lectures

Several Sound Levels can be defined:

2p LecturesSound Pressure Level:

20

10 log effp

pL

p

W Sound Power Level:

0

10 logWWLW

and many more.

p0 = 2·10-5 Pa

W0 = 1·10-12 W


0


Recapitulation from Previous Lectures

Sound power is extremely low.

W WLLectures

0

10 logWWLW

100 10

W

W W

Example:

If the source has a sound power level of 80 dBre10-12

then the sound power equals 10-4 W.



One Source in a Room

diffuse field

source

diffuse field

direct sound

microphone



Direct Sound Only

2 0 0c Wp

source

; 24eff directpr

direct sound

microphone



Diffuse Field

2 0 04 1c Wp ; 1eff diffusepA

microphonemicrophone



Addition of Sound Pressures

2 0 0; 24eff direct

c Wpr

2 0 0;

4 1eff diffusec WpA

Pressures

2 2 2; ; ;eff total eff direct eff diffusep p p

thus (Sabine-Franklin-Jäger theory)

2

4 1110 log4p WL L

A

2g

4p W r A




2 0 0 0 0; 2

4 14eff total

c W c Wpr A

Pressures

Divide by p02

2

; 0 0 0 02 2 2 20 0 0

4 14

eff totalp c W c Wp r p A p

Since p02 equals 0c0W0, this becomes

0 0 0

2

;2 20 0 0

4 14

eff totalp W Wp r W AW


0 0 04p r W AW



This can be rewritten as

2;

4 11ff t t lp W Pressures ;

2 20 0

14

eff totalp Wp W r A

Take the log on both side and multiply with 10

2 4 11p W ;

2 20 0

4 1110log 10log4

eff totalp Wp W r A



Sound pressure level according to

If we rewrite, we get

2 4 11ff t t lp W according to Sabine-Franklin-Jäger theory

;2 20 0

110log 10log 10log4

eff totalp Wp W r A

theory

This equals

4 11 2

4 1110 log4p WL L

r A



Reverberation Radius

The reverberation radius is defined as the distance from the source where both the direct and diffuse sound pressure are equal:sound pressure are equal:

2 2; ;eff direct eff diffusep p

and thus

16 1g

Ar



Example(given earlier)

Ceiling

S (m2)

130

0.5

A (m2)

65

Floor

Side wall left

Side wall right

130

78

78

0.1

0.1

0 2

13

7.8

15 6Side wall right

Front

Back

78

60

60

0.2

0.1

0.1

15.6

6

6

Totals 536 113.4

113.4 0.21536

Room

13 10 6 m3



85

90

ExampleSound Pressure

Lecture room of 13 x 10 x 6 m3 and LW = 86 dB

70

75

80

85

[dB]

Pressure Level 0.02

0.050.100.20

50

55

60

65

SPL,

Lp

[

0.50

1.00 4 11

40

45

50

0 2 4 6 8 10 12

2

110 log4p WL L

r A

distance from source [m]



85

90



70

75

80

85

[dB]

Pressure Level 0.02

0.050.100.20

50

55

60

65

SPL,

Lp

[

0.50

1.00 4 11

High value is not necessarily a good room

40

45

50

0 2 4 6 8 10 12

2

110 log4p WL L

r A

High level means a lot of reverberation

distance from source [m]So again: compromise must be found



Sound Pressure Level with

According to Sab.-Fr.-Jäg. theory SPL reaches a constant level far from the sound source. However, SPL keeps decreasing with increasing distance fromLevel with

Michael Barron’s correction

SPL keeps decreasing with increasing distance from source. Therefore Barron made following correction

correction

2

1 4 0.04010 log exp4

p W

rL Lr A T

which can be written as

/ r mfp /

2

4 1110 log4

r mfp

p WL Lr A

4

tot

VmfpS



85

90



70

75

80

85

[dB]

Pressure Level: Sab-Fr-Jag

0.020.050.100.20

50

55

60

65

SPL,

Lp

[

0.50

1.00

40

45

50

0 2 4 6 8 10 12




85

90



70

75

80

85

[dB]

Pressure Level: Barron 0.02

0.050.100.20

50

55

60

65

SPL,

Lp

[

0.50

1.00

40

45

50

0 2 4 6 8 10 12




Room Acoustics

SpeechSpeech

Noise in Rooms

Multi-Source Situations



Wanted Speech + Noise

wanted speech receiver

wanted speech:Noise a ted speec

- heavily depends on direct sound,

- so room not very important

perceived noise:

noise source

- very often in diffuse field,

- so it depends on the room



Example: Speech with Noise

Reverberation chamber speech + radio

“Ik sta hier in de nagalmkamer op 1 m afstand van deNoise Ik sta hier in de nagalmkamer op 1 m afstand van de mikrofoon. Op 5 meter afstand van de mikrofoon bevindt zich een spelend radiootje. Kunt U mij nog verstaan?”

… Music …………………….

Translation: I am standing here in a reverberation chamber at a distance of 1 m from a microphone At 5 m from thisdistance of 1 m from a microphone. At 5 m from this

microphone a radio is playing. Can you still understand me?




Anechoic room speech + radio

Noise“We bevinden ons in de dode kamer. Op 5 meter afstand van de mikrofoon staat een spelende radio; zelf sta ik op 1 m van de mikrofoon. U merkt wel dat de radio hier

i d hi d lijk i d i d l k ”minder hinderlijk is dan in de nagalmkamer.”

… Music …………………….

Translation: We are now in an anechoic room. At 5 m distance from the microphone a radio is playing; I myself am standing afrom the microphone a radio is playing; I myself am standing a 1 m distance from this microphone. You probably observe that the radio is less annoying than in the reverberation chamber.




Living room speech + radio

Noise“Dit is een stukje tekst opgenomen in een huiskamer die een tikkeltje galmt. De spreker bevindt zich op 1 m van de mikrofoon; op 5 m staat een spelend radiootje. U

kt d t i d t d ij t k t l tmerkt dat, voor iemand met goede oren, mijn tekst wel te volgen is, maar aangenaam is anders, zeker als mijn tekst ook nog veel langer zou duren.”

… Music …………………….

Translation: This is a piece of text recorded in a living roomTranslation: This is a piece of text recorded in a living room which is slightly reverberant. The speaker is distanced 1 m from the microphone; At 5 m from this microphone is a radio. You observe that for someone with good ears my text is intelligible


observe that, for someone with good ears, my text is intelligible, though not pleasantly, particularly if there would be more text.


Example: Speech Levels

Vocal effort Measured at 1 m in front of mouth

Maximum .......................... 90 dB(A)Shouting ........................... 84Very Loud ......................... 78yLoud ................................. 72Raised Voice ...................... 66Normal .............................. 60Relaxed ............................. 54



Some Noise Levels

Some Noise Levels

Damage to the ears ....................... >80 dB(A)Normal speech at 1 m ................... 60

Sleep disturbance ........................ 40Difficult tasks at school or office .... 35-45Traffic noise ................................ 55-75Restaurant .................................. 55-85



Signal to Noise RatioS/N Wanted soundS/N

Noise

Difference between both levels is excellent first estimation



Noisy space Signal strength (= direct sound)

110 logL L 210 log4p WL L

r

n ‘noise’ sources with equal sound strength

4 1

4 110 log 10 logp WL L n

A

4 110 logp W

nL L

A



S/N ratio Signal

110 logL L 210 log4p WL L

r

Noise

4 110 l

nL L

10 logp WL LA

S/N= Signal – Noise

Th ll ti f L


Thus a cancellation of LW


S/N ratio Signal to noise ratio is then defined as

4 11 n 2

4 11/ 10 log 10 log4

nS N

r A

S/N depends on:- distance to wanted speaker r- distance to wanted speaker r- number of noise sources in the room n- total absorption (including guests) A- mean absorption coefficient



Speech Intelligibility

Minimum level for good ears S/N = -6Fair S/N = 0Good S/N =+6Good S/N +6

For a whole day at school, higher values required

Also for the hearing impaired S/N = +15 !!!!!



Example of a Restaurant

r n gem lbh Signal Noise S/N

1 10 0 1 13 10 6 59 0 68 3 9 31 10 0.1 13106 59.0 68.3 -9.3

The person speaking here is inaudible.

Yet, such spaces are still designed and built.

l l f d S/ 6Minimum level for good ears S/N = -6Fair S/N = 0Good S/N =+6



Example of a Restaurant (1)


1 10 0 1 13 10 6 59 0 68 3 9 31 10 0.1 13106 59.0 68.3 -9.3

0.5 10 0.1 13106 65.0 68.3 -3.3

0.25 10 0.1 13106 71.0 68.3 2.70.25 10 0.1 13106 71.0 68.3 2.7

Distance to source is an important factor.






1 1 0 1 13 10 6 59 0 58 3 0 71 1 0.1 13106 59.0 58.3 0.7

1 5 0.1 13106 59.0 65.3 -6.3

1 25 0.1 13106 59.0 72.3 -13.21 25 0.1 13106 59.0 72.3 13.2

Number of unwanted sources is important.






1 5 0 1 13 10 6 59 0 65 3 6 31 5 0.1 13106 59.0 65.3 -6.3

1 5 0.2 13106 59.0 61.3 -2.3

1 5 0.3 13106 59.0 59.4 -0.41 5 0.3 13106 59.0 59.4 0.4

Mean absorption coefficient is important.






1 5 0 2 6 5 5 3 59 0 67 8 8 81 5 0.2 6.553 59.0 67.8 -8.8

1 5 0.2 13106 59.0 61.7 -2.7

1 5 0.2 262012 59.0 55.5 3.51 5 0.2 262012 59.0 55.5 3.5

Total area is important as well.




S/N ratio Lombard effect (1911)

People tend to talk louder in a reverberant space.

And the more people are present, the louder they speak.

However,

this effect is not reflected in the S/N ratio.



Room Acoustics

Auditorium Acoustics: Strength / LoudnessAuditorium Acoustics: Strength / Loudness



Strength / Loudness (1)

One measure often used to characterise auditoriums for music is strength, G.

It is defined as the amount of energy at a certain iti i th l ti t th t fposition in the room relative to the amount of

energy at a distance of 10 m from the source in an anechoic room.

2 ( )t

effp t dt0

2,10

0

10 log( )

t

A m

Gp t dt


0



G (dB) characterises the influence of the room on sound pressure level relative to an anechoic situationsituation.

It b ittIt can be written as

1 4(1 ) 2

2

( )410 log 1

r AG

24 10




At a large distance from the sound source (r >2rg) this can be approximated as

21 4(1 )

4(1 )410 log 10 log 31r AG

2

10 log 10 log 3114 10

GA



30

ExampleLoudness / Strength

Concert Hall of 20 x 50 x 14 m3

15

20

25dB

]

Strength

0.02 0 05

too loud,headaches

5

10

15

Stre

ngth

, G [ 0.05

0.10 0.20

0 505.5 dB4 0 dB

-10

-5

00 10 20 30 40 50

S 0.50

1.00 too weak,inaudible

4.0 dB

10





According to this classical theory, the strength/loudness becomes constant at large distance from the sourcedistance from the source.

I lit G k d i if iIn reality G keeps decreasing if r increases.

A i h Mi h l B ’ ti liAgain here Michael Barron’s correction applies.



Room Acoustics

Auditorium AcousticsAuditorium Acoustics




This book contains 100 concert halls from all over the world.

Among these halls are ‘het Concertgebouw’ in A t d d ‘d D l ’ i R tt dAmsterdam and ‘de Doelen’ in Rotterdam.

The book also contains questionnaires among musicians and audience.



Concert Halls

Concertgebouw


ConcertgebouwAmsterdam



Concert Halls

Doelen


Doelen Rotterdam



Concert Halls

Doelen

Amsterdam versus Rotterdam

1888Doelen Rotterdam

year 1888

2037 seats

18780 318780 m3

year 1966

2242 seats

24070 m3




Beranek uses among others 4 measures for characterising concert halls:

Parameters - Reverberation time

- Bass ratio

- Strength / Loudness

- Degree of diffusivity




A concert hall does not contain much absorption from its own. Absorption mainly results from audience

Absorptionaudience.

K t ’ ti ti (‘D l ’)Kosten’s reveration equation (‘Doelen’):

VT 6 1.07

Tseated area




Bass ratio is defined as a ratio of reverberation times at different frequencies:

Bass Ratio125 250

500 1000

T TBRT T

People tend to like that T is longer at lower f

500 1000

frequencies.

1.1 < BR < 1.45 for ‘short’ T (chamber music)

1.1 < BR < 1.25 for ‘long’ T (auditorium)




Strength / Loudness has already been defined previously.

Strength / Loudness




In a completely diffuse sound field a listener in the audience feels completely enveloped by the sound.

DiffusivityTo increase diffusivity use scattering elements with th i f l th i dit i ( 50 ?)the size of wave lengths in auditorium (…50 cm?)

h l d h k f h ’ (fl h ’ )This also reduces the risk of echo’s (flutter echo’s)




Very often concert halls are built in a shoebox shape, like the ‘Musikverein’ in Vienna:

Shoebox Shape

- Reduces risk of errors

- More constant distribution of important parameters thacross the room

- Seats below a balcony often notorious for bad soundsound

- Risk of flutter echo’s between opposite walls

Other shapes are of course possible too.




Two of Beranek’s parameters:

- Reverberation time, T: between 2.0 – 2.3 s

ParametersRevisited

- Strength / Loudness, G: between 4.0 and 5.5 dB

A simple Excel sheet can now be used as a first estimate.




With pencil and paper a good estimate of a concert hall can be made (70% ???)

Modern simulation software is an important tool (80% ???)(80% ???)

l d ll h l d l dFor large auditoriums still physical models are made and tested (90% ???)

The remaining 10% is pure psychology, PR and luck.



That’s it for today!End

More information on room acoustics can be found here

htt //bk ij t / b L Nij (D t h l )•http://bk.nijsnet.com/ by Lau Nijs (Dutch only)

•“Concert and Opera Houses – How they sound” by L.L. BeranekL.L. Beranek

•“Auditorium Acoustics and Architectural Design” by M. Barron


ar2ae045-ra1 room acoustics 1

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