Small Room Acoustics Ben Kok Nelissen ingenieursbureau b

Small Room Acoustics Ben Kok Nelissen ingenieursbureau b. kok@nelissenbv. nl AES tutorial, 2008 1

Introduction • What is a sound wave? AES tutorial, 2008 2

Sound wave AES tutorial, 2008 3

Sound wave F = 100 Hz → λ = 3, 4 m F= 1 k. Hz → λ = 0, 34 m F = 10 k. Hz → λ = 0, 034 m AES tutorial, 2008 4

When do we consider a room ‘Small’? AES tutorial, 2008 5

Small Rooms • • • Living Room Recording Studio Control Room Car Telephone Booth Headphone AES tutorial, 2008 6

Low frequencies in an enclosure AES tutorial, 2008 7

Low frequencies in an enclosure AES tutorial, 2008 8

Low frequencies in an enclosure “Golden” ratios: ASHREA 1: 1. 17: 1. 47 ASHREA 1: 1. 45: 2. 10 Bolt 1: 1. 28: 1. 54 IAC 1: 1. 26: 1. 60 Seppmeyer 1: 1. 14: 1. 39 Kok 1: 1. 12: 1. 41 AES tutorial, 2008 9

Room mode analysis AES tutorial, 2008 10

absorption • porous material • resonators • sandwich constructions AES tutorial, 2008 11

porous material AES tutorial, 2008 12

porous material AES tutorial, 2008 13

porous material AES tutorial, 2008 14

porous material Rule of thumb: AES tutorial, 2008 15

resonator AES tutorial, 2008 16

diafragmatic resonator AES tutorial, 2008 17

diafragmatic resonator flexible panels • thin • large • high internal loss excited over the full area AES tutorial, 2008 18

Helmholtz resonator AES tutorial, 2008 19

diffusion spatial and temporal distribution of energy AES tutorial, 2008 20

Specular reflection AES tutorial, 2008 21

Diffuse reflection 1 AES tutorial, 2008 22

Diffuse reflection 2 AES tutorial, 2008 23

diffuser example AES tutorial, 2008 24

diffusion repetition of the same sequence should be avoided!! > grating lobes! AES tutorial, 2008 25

phase modulated array of diffusers AES tutorial, 2008 26

installation example AES tutorial, 2008 27

microphone/ loudspeaker placement • early reflections (1 st 10 ms) cause coloration • specular reflections (narrow peak) cause comb filtering • diffuse reflections add ‘warmth’ AES tutorial, 2008 28

microphone/ loudspeaker placement • distant micing/ listening allows sound to develop • close micing/ listening minimizes room influence • a small room has no statistic sound field, strong variation between positions can exist AES tutorial, 2008 29

microphone/ loudspeaker placement • room modes have a significant influence on low frequency coupling; loudspeaker position can have a strong influence on low frequency response • distributed sub-woofers can create a smoother low frequency response • a small room has no statistic sound field, strong variation between positions can exist AES tutorial, 2008 30

conclusion • a small room behaves different because it’s dimensions are similar to the wavelength of the (re)produced sound • source and listening positions often are fixed -> the design can accommodate for this • changing positions can have a dramatic influence AES tutorial, 2008 31

QUESTIO NS AES tutorial, 2008 32