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

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 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

The project: a ”sonic chandelier” • S.Elisabetta church (reverb time 5 sec ) • Sonic chandelier: o Moving virtual sources (WFS) o Active insulation 1 2 3 10/09/2008

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

Sound focalization by WFS (Delft University of Technology, 90’s) Array Sensible parameters: concave r A Set the beam A focus λ λ width.. Δ x Spatial aliasing , convex λ secondary lobes.. The front curvature is obtained by means of a gain ‐ delay set .. Delays Common filter Gains 10/09/2008

The spatial aliasing problem The spatial Nyquist theorem: λ λ = > ⋅Δ Sampling condition: 2 x ϕ x sen c ⇒ ≤ f antialiasing sampling filter Δ ϕ max 2 xsen Reconstruction condition: c ϑ ≤ 2 sen ( f ) Δ em xf Omnidirectional Rigid pistons 10/09/2008

Our choice: single transducer, extended range c ϑ ≤ 2 sen ( f ) Δ em 10/09/2008 xf

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

Chandellier: design, manifacturing and assembling 10/09/2008

Lifting up.. 10/09/2008

Speakers to channel connection Special 32 Ohm model by Ciare, Italy 228 loudspeakers 1 channel 64 channels 10/09/2008 Frounhofer distance for a group of speaker at 10 kHz is about 4 meters

More on the sound field.. 500 Hz concave 1 kHz A λ main focus convex 2 kHz Absorbtion 10/09/2008

The feeding system 64 output channels 10/09/2008

From WFS to filter structure Common WFS EQ Antialiasing Antialiasing Single Gains and and speaker EQ sampling reconstruction speaker delays (mag and phase) filter filter relative EQ Dynamic Array delays ‐ gains Speaker Input FIR Output FIRs shape matrix , directivity Output FIRs concave A λ main focus 256 taps 4096 Inverse filtering.. taps 10/09/2008 convex

Output FIR design Output FIRs Inverse filtering (Ole Kirkeby) 10/09/2008

Input FIR design 10/09/2008

From filter to SW structure Array Dynamic Speaker Input FIR Output FIRs shape delays+gains directivity WFS focus “WFS focus” SW _ _ _ _ _ _ Brutefir SW input FIR WFS focus : dynamic gains and delays By Daniele Torelli and Fons Adriaensen 64 BRUTEFIR Ch “WFS focus” 64 Ch 64 Ch By MADI S1 Anders OUT S2 + “WFS focus” Torger 64 Ch ….. … “WFS focus” 64 Ch S5 10/09/2008

Moving the focus: “WFS focus” concept Spatial information 64 Input FIR Sample rate DYNAMIC Ch Output convolution, doubling, FRACTIONAL DELAY FIRs SR = 48 kHz 96 kHz and GAINS Effect of a fractional delay with linear interpolation. 10/09/2008

User interfaces MIDI MADI inputs OSC controller (external sources) MIDI “WFS focus” 64 Ch Mono + signals “WFS focus” ….. 64 Ch ….. “WFS focus” 64 Ch AUDIO signal SPACE control Audio OSC application, I.E. “ARDOUR” ARDOUR Spherical coordinates centered on main “WFS focus” focus � fractional delay and gains 10/09/2008 plugin

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 one shell) . Tested with filtered pink noise. • Very sensible increasing of the active insulation with people beneath the array 10/09/2008

Thank you ! 10/09/2008