1aes tutorial, 2008 small room acoustics ben kok nelissen ingenieursbureau [email protected]
TRANSCRIPT
AES tutorial, 2008AES tutorial, 2008 11
Small Room AcousticsSmall Room Acoustics
Ben KokBen KokNelissen ingenieursbureauNelissen [email protected]@nelissenbv.nl
AES tutorial, 2008AES tutorial, 2008 22
IntroductionIntroduction
• What is a sound wave?What is a sound wave?
AES tutorial, 2008AES tutorial, 2008 33
(peff)
Verdichting Verdunning
Sound waveSound wave
f
c
AES tutorial, 2008AES tutorial, 2008 44
Sound waveSound wave
f
c
(peff)
Verdichting Verdunning
F = 100 Hz → F = 100 Hz → λλ = 3,4 m = 3,4 m
F = 1 kHz → F = 1 kHz → λλ = 0,34 = 0,34 mm
F = 10 kHz → F = 10 kHz → λλ = 0,034 = 0,034 mm
AES tutorial, 2008AES tutorial, 2008 55
pressurezone
eigenmodes diffraction specular reflections
f1.0.0 f c 4×f c
When do we consider a room When do we consider a room ‘Small’?‘Small’?
A
VT
V
Tfc
6
2000
AES tutorial, 2008AES tutorial, 2008 66
Small RoomsSmall Rooms
• Living RoomLiving Room• Recording StudioRecording Studio• Control RoomControl Room • CarCar• Telephone BoothTelephone Booth• HeadphoneHeadphone
AES tutorial, 2008AES tutorial, 2008 77
length = l
Low frequencies in an Low frequencies in an enclosureenclosure
c
l
cf
20
02 f
.etc
AES tutorial, 2008AES tutorial, 2008 88
Low frequencies in an Low frequencies in an enclosureenclosure
222
,, 2
z
x
y
x
x
xnnn l
n
l
n
l
ncf
zyx
AES tutorial, 2008AES tutorial, 2008 99
Low frequencies in an Low frequencies in an enclosureenclosure““Golden” ratios:Golden” ratios:
ASHREAASHREA1:1.17:1.471:1.17:1.47
ASHREAASHREA1:1.45:2.101:1.45:2.10
BoltBolt1:1.28:1.541:1.28:1.54
IACIAC 1:1.26:1.601:1.26:1.60
SeppmeyerSeppmeyer1:1.14:1.391:1.14:1.39
KokKok 1:1.12:1.411:1.12:1.41
AES tutorial, 2008AES tutorial, 2008 1010
Room mode analysisRoom mode analysisEigenmode verdeling in rechthoekige ruimte
date 1,2589255,165 4,103 3,657 25-apr-08 1,778279
X Y Z Volume7 4,1 2,7 m 77 m 3̂Nx Ny Nz Fres Density 1/40 0 0 0,0 0,21 0 0 24,5 0,2 3,500 1 0 41,8 0,6 2,051 1 0 48,5 1,7 1,772 0 0 49,0 21,7 1,750 0 1 63,5 1,0 1,352 1 0 64,4 16,4 1,331 0 1 68,1 4,3 1,263 0 0 73,5 3,1 1,170 1 1 76,1 6,9 1,131 1 1 79,9 4,8 1,072 0 1 80,2 58,3 1,070 2 0 83,7 5,6 1,033 1 0 84,6 21,5 1,011 2 0 87,2 7,8 0,982 1 1 90,5 6,3 0,952 2 0 97,0 3,5 0,883 0 1 97,1 117,7 0,884 0 0 98,0 26,5 0,880 2 1 105,0 3,5 0,823 1 1 105,8 33,7 0,814 1 0 106,6 31,3 0,801 2 1 107,9 19,1 0,803 2 0 111,4 7,4 0,772 2 1 115,9 5,9 0,744 0 1 116,8 30,8 0,73
Optimum Eigenmode distribution
0,1
1,0
10,0
100,0
10,0 100,0 1000,0
Frequency
Density
Room OptimumSort
AES tutorial, 2008AES tutorial, 2008 1111
absorptionabsorption
•porous materialporous material• resonatorsresonators•sandwichsandwich constructionsconstructions
AES tutorial, 2008AES tutorial, 2008 1212
porous materialporous material
AES tutorial, 2008AES tutorial, 2008 1313
porous materialporous material40 mm
40 mm
40 mm 150 mm
AES tutorial, 2008AES tutorial, 2008 1414
porous materialporous material
0
0,2
0,4
0,6
0,8
1
1,2
125 250 500 1000 2000
200 mm spouw
50 mm spouw
AES tutorial, 2008AES tutorial, 2008 1515
porous materialporous material
Hzfmd
df
c
c
10010,0
10
Hzfmd c 5020,0
Rule of thumb:Rule of thumb:
Hzfmd c 20005,0
AES tutorial, 2008AES tutorial, 2008 1616
resonatorresonator
AES tutorial, 2008AES tutorial, 2008 1717
diafragmatic resonatordiafragmatic resonator
mdfc
60
Hzf
md
kgm
c 100
12,0
3
AES tutorial, 2008AES tutorial, 2008 1818
diafragmatic resonatordiafragmatic resonator
flexible panelsflexible panels
•thinthin
•largelarge
•high internal losshigh internal loss
excited over the fullexcited over the full areaarea
AES tutorial, 2008AES tutorial, 2008 1919
length = l
volume = v mass = m area = s
Helmholtz resonatorHelmholtz resonator
Vl
scfc 2
AES tutorial, 2008AES tutorial, 2008 2020
diffusiondiffusion
spatial spatial andand temporal distribution of temporal distribution of energyenergy
AES tutorial, 2008AES tutorial, 2008 2121
Specular reflectionSpecular reflection
AES tutorial, 2008AES tutorial, 2008 2222
Diffuse reflection 1Diffuse reflection 1
AES tutorial, 2008AES tutorial, 2008 2323
Diffuse reflection 2Diffuse reflection 2
AES tutorial, 2008AES tutorial, 2008 2424
diffuser examplediffuser example
AES tutorial, 2008AES tutorial, 2008 2525
diffusiondiffusion
repetition of the same sequence repetition of the same sequence should be avoided!!should be avoided!!
> grating lobes!> grating lobes!
AES tutorial, 2008AES tutorial, 2008 2626
phase modulated array of phase modulated array of diffusersdiffusers
0 90 270 180 90 0 270 180
270 90 0 180 270 90
0 90 180 270 0 90 270 180
Side Wall LeftRear Front
Front WallLeft Right
Side Wall RightFront Rear
AES tutorial, 2008AES tutorial, 2008 2727
installation exampleinstallation example
AES tutorial, 2008AES tutorial, 2008 2828
microphone/ loudspeaker microphone/ loudspeaker placementplacement• early reflections (1early reflections (1st st 10 10
ms) cause colorationms) cause coloration• specular reflections specular reflections
(narrow peak) cause (narrow peak) cause comb filteringcomb filtering
• diffuse reflections add diffuse reflections add ‘warmth’‘warmth’
AES tutorial, 2008AES tutorial, 2008 2929
microphone/ loudspeaker microphone/ loudspeaker placementplacement• distant micing/ listening allows distant micing/ listening allows
sound to developsound to develop• close micing/ listening minimizes close micing/ listening minimizes
room influenceroom influence• a small room has no statistic a small room has no statistic
sound field, strong variation sound field, strong variation between positions can existbetween positions can exist
AES tutorial, 2008AES tutorial, 2008 3030
microphone/ loudspeaker microphone/ loudspeaker placementplacement• room modes have a significant room modes have a significant
influence on low frequency coupling; influence on low frequency coupling; loudspeaker position can have a strong loudspeaker position can have a strong influence on low frequency responseinfluence on low frequency response
• distributed sub-woofers can create a distributed sub-woofers can create a smoother low frequency responsesmoother low frequency response
• a small room has no statistic sound a small room has no statistic sound field, strong variation between field, strong variation between positions can existpositions can exist
AES tutorial, 2008AES tutorial, 2008 3131
conclusionconclusion
• a small room behaves different a small room behaves different because it’s dimensions are similar because it’s dimensions are similar to the wavelength of the to the wavelength of the (re)produced sound(re)produced sound
• source and listening positions source and listening positions often are fixed -> the design can often are fixed -> the design can accommodate for thisaccommodate for this
• changing positions can have a changing positions can have a dramatic influencedramatic influence
AES tutorial, 2008AES tutorial, 2008 3232
QUESTIOQUESTIONSNS