A digitally controlled two dimensional loudspeaker array Paolo - - PowerPoint PPT Presentation

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A digitally controlled two dimensional loudspeaker array Paolo - - PowerPoint PPT Presentation

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A digitally controlled two dimensional loudspeaker array Paolo Martignon (paolo.martignon@inwind.it) Fons Adriaensen (LAE Group) Daniele Torelli Angelo Farina (LAE Group) AES 32th Conference 10/09/2008 DSP for loudspeakers The full staff: LAE

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SLIDE 1

A digitally controlled two dimensional loudspeaker array

Paolo Martignon (paolo.martignon@inwind.it) Fons Adriaensen (LAE Group) Daniele Torelli Angelo Farina (LAE Group)

10/09/2008 AES 32th Conference DSP for loudspeakers

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SLIDE 2

The full staff: LAE and..

Project management, geometry and filter design SW development on Linux PC Consultance on SW, HW and algorithms Wiring design and realization Place, instrumentation, hardware help and consultance Chandelier iron structure realization

10/09/2008

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SLIDE 3

The project: a ”sonic chandelier”

  • S.Elisabetta church (reverb time 5 sec )
  • Sonic chandelier:
  • Moving virtual sources (WFS)
  • Active insulation

1 2 3 10/09/2008

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SLIDE 4

Presentation outline

  • Wave Field Synthesis concepts, spatial

aliasing

  • Speakers choice and line array prototype
  • 2D array design and realization
  • HW description and signal processing scheme
  • Filters structure, design and implementation
  • Validation test and measurement

10/09/2008

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SLIDE 5

Sound focalization by WFS

(Delft University of Technology, 90’s)

Array Sensible parameters: The front curvature is obtained by means of a gain‐delay set ..

A λ

convex focus concave

A λ

x λ Δ

Set the beam width.. Spatial aliasing, secondary lobes.. Gains Delays Common filter r

10/09/2008

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SLIDE 6

The spatial aliasing problem

max

2 2

x

x sen c f xsen λ λ ϕ ϕ = > ⋅Δ ⇒ ≤ Δ

xf c f sen

em

Δ ≤ 2 ) ( ϑ

The spatial Nyquist theorem:

Sampling condition: Reconstruction condition: antialiasing sampling filter

10/09/2008

Omnidirectional Rigid pistons

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SLIDE 7

Our choice: single transducer, extended range

xf c f sen

em

Δ ≤ 2 ) ( ϑ

10/09/2008

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SLIDE 8

A simplified prototype

  • 24 channel line array
  • Plays the role of a scale model of the

disc, though it is not

  • Diametral section of the disc
  • The 3D effect of the disc is projected on a

plane

  • Algorithm production and testing, speaker

testing

10/09/2008

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SLIDE 9

Chandellier: design, manifacturing and assembling

10/09/2008

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SLIDE 10

Lifting up..

10/09/2008

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SLIDE 11

Speakers to channel connection

1 channel

Special 32 Ohm model by Ciare, Italy

228 loudspeakers 64 channels Frounhofer distance for a group of speaker at 10 kHz is about 4 meters

10/09/2008

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SLIDE 12

More on the sound field..

Absorbtion 1 kHz 2 kHz 500 Hz

A λ

convex main focus concave

10/09/2008

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SLIDE 13

The feeding system

64 output channels

10/09/2008

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SLIDE 14

From WFS to filter structure

Common WFS EQ and speaker EQ (mag and phase) Antialiasing sampling filter Gains and delays Antialiasing reconstruction filter Single speaker relative EQ Input FIR Array shape Dynamic delays‐gains matrix , Output FIRs Speaker directivity Output FIRs

A λ

convex main focus concave 256 taps 4096 taps

10/09/2008

Inverse filtering..

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SLIDE 15

Output FIR design

Output FIRs Inverse filtering (Ole Kirkeby)

10/09/2008

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SLIDE 16

Input FIR design

10/09/2008

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SLIDE 17

From filter to SW structure

“WFS focus” SW _ _ _ WFS focus SW _ _ _ Brutefir Input FIR Array shape Dynamic delays+gains Speaker directivity Output FIRs

WFS focus: By Daniele Torelli and Fons Adriaensen input FIR dynamic gains and delays

“WFS focus” BRUTEFIR By Anders Torger MADI OUT “WFS focus” “WFS focus” ….. S1 S2 … S5

+

64 Ch 64 Ch 64 Ch 64 Ch 64 Ch

10/09/2008

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SLIDE 18

Moving the focus: “WFS focus” concept

Sample rate doubling, 96 kHz Input FIR convolution, SR = 48 kHz DYNAMIC FRACTIONAL DELAY and GAINS Output FIRs 64 Ch Effect of a fractional delay with linear interpolation. Spatial information

10/09/2008

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SLIDE 19

User interfaces

“WFS focus” “WFS focus” “WFS focus” …..

+

64 Ch 64 Ch 64 Ch ….. MADI inputs (external sources) Audio application, I.E. “ARDOUR” OSC MIDI controller MIDI ARDOUR “WFS focus” plugin OSC AUDIO signal SPACE control Spherical coordinates centered on main focus fractional delay and gains

10/09/2008

Mono signals

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SLIDE 20

Results

  • Precise and smooth, “click” free sound moving
  • Appreciable Doppler effect
  • “Objective” sound scene
  • Good distance perception
  • 22 dB decay at medium frequencies between the

center and a peripheral point 5 m distant (center of

  • ne shell) . Tested with filtered pink noise.
  • Very sensible increasing of the active insulation

with people beneath the array

10/09/2008

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SLIDE 21

Thank you !

10/09/2008