Akustisches Kolloquium Electroacoustic absorption: towards room equalization in the low- frequency range Dr. Hervé Lissek EPFL STI IEL LTS2

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Presentation transcript:

Akustisches Kolloquium Electroacoustic absorption: towards room equalization in the low- frequency range Dr. Hervé Lissek EPFL STI IEL LTS2

Akustisches Kolloquium What is this sound ? H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 2 10/28/2015

Akustisches Kolloquium Outline Context: room modes in the low-frequency range Presentation of the Electroacoustic Absorber concept Practical realization Application to room modes damping H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 3 10/28/2015

Akustisches Kolloquium 1. Context 4 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 5 Low-frequency in music 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Room modes characterization: standing waves In 1 dimension, with 2 ideally rigid walls 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 6 Problems of LF room acoustics 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Particle velocity Sound pressure nodes antinodes

Akustisches Kolloquium Room modes characterization: standing waves In 3 dimensions 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 7 Problems of LF room acoustics 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping nodes antinodes

Akustisches Kolloquium Room modes characterization: standing waves  uneven spatial distribution of sound energy, depending on frequency 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 8 Problems of LF room acoustics 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Room modes characterization: frequency response  dominated by strong peaks (resonances) and dips (anti-resonances) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 9 Problems of LF room acoustics 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Corner #2 Center of the room Source

Akustisches Kolloquium Room modes characterization: modal decay time  sustain at the various resonance frequencies once the source stops  definition of MT 60 (see RT 60 ) – may strongly vary with frequency 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 10 Problems of LF room acoustics 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Music rendering issue in the low-frequency range 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 11 Problems of LF room acoustics 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Low-frequency noise issue 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 12 Problems of LF room acoustics 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Optimal placement of subwoofers Solutions of the state of the art Source: 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 13

Akustisches Kolloquium In-line equalization Solutions of the state of the art 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 14

Akustisches Kolloquium Sound absorption: the room resonances are due to reflections on walls Solutions of the state of the art prpr fluid (air) material pipi 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 15  provide absorption in the LF range?

Akustisches Kolloquium State of the art sound absorbers  inefficient in the LF range (see /4 rule) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 16 Solutions of the state of the art Porous materials Helmholtz resonators Panel absorbers absorption LF 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium State of the art sound absorbers  bass-traps (membrane absorbers) Efficient LF narrow-band (1 resonance frequency) sound absorbers 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Context2. Electroacoustic absorber3. Realizations4. Room modes damping Solutions of the state of the art Source: T. Cox and P. D’Antonio, Acoustic absorbers and diffusers, Taylor & Francis Publ., 2009

Akustisches Kolloquium State of the art sound absorbers  bass-traps (membrane absorbers) Efficient LF narrow-band (1 resonance frequency) sound absorbers  e-traps (active bass traps) Efficient on 2 (adjustable) resonance frequencies 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 18 E-trap 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Solutions of the state of the art

Akustisches Kolloquium Active modal control with multiple subwoofers Opposite phase, opposite direction Controlled Acoustic Bass System (CABS) Active noise control solution Source: S. B. Nielsen and A. Celestinos. "Low frequency sound field control in rectangular listening rooms using CABS (Controlled Acoustic Bass System) will also reduce sound transmission to neighbor rooms." Forum Acusticum /28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 19

Akustisches Kolloquium 2. The concept of Electroacoustic Absorption 20 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Development of an active sound absorption solution with  >0.83 along the range [ Hz] Based on actuated membranes (loudspeakers) used as membrane absorbers The electric load of the loudspeaker acts as an additional acoustic impedance for the membrane 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 21 Electroacoustic absorbers H. Lissek, R. Boulandet, and R. Fleury, “Electroacoustic absorbers: bridging the gap between shunt loudspeakers and active sound absorption”, J. Acoust. Soc. Am., 129(5), , (2011). 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium The acoustic impedance at the diaphragm can be set as 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 22 Passive electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Diaphragm acoustic impedance

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 23 Passive electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Ex1: open circuit (i=0) Acoustic impedance

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 24 Passive electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Normalized acoustic admittance ParameterDescriptionValueUnit M ms Moving mass13.0g R ms Mechanical resistance0.8N.s.m -1 C ms Mechanical compliance120  m.N -1 ReRe Electrical resistance5.6  LeLe Electrical inductance0.9mH SdSd Membrane surface133cm 2 BlForce factor6.9N.A -1 VbVb Cabinet volume10dm 3  Air mass density1.2kg/m 3 cSound celerity in air343m.s -1 Ex1: open circuit (i=0)

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 25 Passive electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Normalized acoustic admittance Ex1: open circuit (i=0) ParameterDescriptionValueUnit M ms Moving mass13.0g R ms Mechanical resistance0.8N.s.m -1 C ms Mechanical compliance120  m.N -1 ReRe Electrical resistance5.6  LeLe Electrical inductance0.9mH SdSd Membrane surface133cm 2 BlForce factor6.9N.A -1 VbVb Cabinet volume10dm 3  Air mass density1.2kg/m 3 cSound celerity in air343m.s -1

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 26 Passive electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Sound absorption coefficient ParameterDescriptionValueUnit M ms Moving mass13.0g R ms Mechanical resistance0.8N.s.m -1 C ms Mechanical compliance120  m.N -1 ReRe Electrical resistance5.6  LeLe Electrical inductance0.9mH SdSd Membrane surface133cm 2 BlForce factor6.9N.A -1 VbVb Cabinet volume10dm 3  Air mass density1.2kg/m 3 cSound celerity in air343m.s -1 Ex1: open circuit (i=0)

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 27 Passive electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Sound absorption coefficient Ex2: shunt RLC s=js=j

Akustisches Kolloquium Ex2: shunt RLC 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 28 Passive electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Ex3: (p,v) feedback control (aka direct impedance control) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 29 Active electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Ex3: (p,v) feedback control (aka direct impedance control) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 30 Active electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Ex4: electric impedance synthesis approach 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 31 Active electroacoustic absorbers Characteristic equations Control law Lissek et al., Electroacoustic absorbers: bridging the gap between shunt loudspeakers and active sound absorption, JASA 129 (5), Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium After the duality between the acoustic and electric impedances, there exists:  a unique acoustic impedance for each electric load  a unique electric load for each acoustic impedance  the idea is to identify the electric load achieving a desired acoustic impedance  Methodology: 1.Define a target acoustic impedance Z at 2.Identify the corresponding electric load Y eq Active electroacoustic absorbers H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 32 Target resistance Need to set reactive terms for stability 10/28/2015 Ex4: electric impedance synthesis approach 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Note: we need to implement Y eq rather than Z eq for sake of causality

Akustisches Kolloquium Active electroacoustic absorbers H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 33 10/28/2015 Ex4: electric impedance synthesis approach 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Active electroacoustic absorbers Ex4: electric impedance synthesis approach Such loads are complex to realise with analog devices: Design of digital filters on FPGA platform to mimic a desired electrical admittance at the loudspeaker terminals Use a voltage-current converter to deliver a current to the loudspeaker H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 34 IIR filter generating CompactRIO® real-time controller 10/28/ Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Active electroacoustic absorbers Ex5: «specific feedforward» approach The synthetic electric admittance Y eq acts as a current command, based on the sensing of the emf e. What if we substitue the pressure p for the emf e as the input? This new technique has been recently developped in the lab, which shall improve the closed-loop stability (  bandwidth extension) H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 35 Source of instability 10/28/ Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium ptpt controller Ex5: «specific feedforward» approach Specification of a target acoustic impedance: Hybrid solution of the admittance synthesis and feedback control Use of sensor (microphone) and digital controller : usefull : source of instability Transfer function (p  i) Θ p : Always stable (only dependant on the coupling with the room) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 36 Active electroacoustic absorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping specific feedforward

Akustisches Kolloquium A desired acoustic impedance Z at can be assigned by identifying the controller transfer function: H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 37 ptpt v 10/28/ Context2. Electroacoustic absorber3. Realizations4. Room modes damping Electroacoustic absorbers Ex5: «specific feedforward» approach

Akustisches Kolloquium 3. Practical realization 38 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Eigenfrequency study with Comsol Multiphysics Room CAD of the targeted room Define a given uniform real acoustic resistance R wall for walls to fit with measurements Absorbers Same acoustic resistance R a on all diaphragms result: eigenfrequencies in [20 – 100 Hz] 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range FEM simulation R wall RaRa 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Eigenvalues  modal decay times 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range FEM simulation 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Karkar et al., Electroacoustic absorbers for the low-frequency modal equalization of a room: what is the optimal target impedance for maximum modal damping, depending on the total area of absorbers?, Forum Acusticum 2014

Akustisches Kolloquium Changing the value of resistance R a  for each mode, find the minimal value of MT60  translate as a frequency-dependant resistance R a (f) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Optimal acoustic resistance zoom 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Karkar et al., Electroacoustic absorbers for the low-frequency modal equalization of a room: what is the optimal target impedance for maximum modal damping, depending on the total area of absorbers?, Forum Acusticum 2014

Akustisches Kolloquium Changing the value of resistance R a  for each mode, find the minimal value of MT60  translate as a frequency-dependant resistance R a (f) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Optimal acoustic resistance 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Karkar et al., Electroacoustic absorbers for the low-frequency modal equalization of a room: what is the optimal target impedance for maximum modal damping, depending on the total area of absorbers?, Forum Acusticum 2014

Akustisches Kolloquium Changing the value of resistance R a  for each mode, find the minimal value of MT60  translate as a frequency-dependant resistance R a (f) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Optimal acoustic resistance 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Karkar et al., Electroacoustic absorbers for the low-frequency modal equalization of a room: what is the optimal target impedance for maximum modal damping, depending on the total area of absorbers?, Forum Acusticum 2014

Akustisches Kolloquium The function R a (f) serve as a specification for the electroacoustic absorbers impedance Z at (f)=R at (f)+i  X at (f) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Acoustic impedance specification 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Implementation in the prototype 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Implementation Voltage-driven current amplifier Filter implemented on a DSP platform DSP 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Implementation in the prototype 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 46 Electroacoustic absorbers CompactRIO® real-time controller Voltage-driven current amplifier 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 47 Electroacoustic absorbers ISO : acoustic impedance measurement technique Acoustic impedanceAbsorption coefficient 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium 4. Room modes damping: experimental assessment 48 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium 4x4 electroacoustic absorbers prototypes (total surface = 16x151 cm 2 = 0.24 m 2 ) In a reverberant chamber of m 2  evaluation of room modal damping 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 49 Experimental assessment 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium 1.Frequency response without and with absorbers  identify individual room modes  assess damping performance on peaks and dips amplitudes 2.Modal decay times without and with absorbers  assess damping performance in the time domain 3.Recording of music rendering, without and with absorbers  listen to the effect on music rendering 4.Recording of kick drum, without and with absorbers  listen to the effect on acoustic music playing 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 50 Experimental assessment 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Hardware Recorders/analyzers B&K Pulse (frequency responses) frequency resolution: 31.5 mHz M-Audio M-Track 8 soundcard (recordings) Microphones Sources Facility (reverberant chamber, V=215.6 m 3, S=226.9 m 2 ) Subwoofer Kick drum (Pearl Export) PCB 130D20 (frequency responses) Beyerdynamic M101 N (recordings) Supplementary panel absorber 4 electroacoustic absorbers at the 4 room corners 7 microphone positions 51 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 10/28/ Context2. Electroacoustic absorber3. Realizations4. Room modes damping Experimental assessment

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Frequency response (blue: «Hardwalls», red: «Absorbers») 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Modal damping (dB) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Frequency response 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Mode 8 – waveforms (hardwalls : Hz - absorbers : Hz) Mode 8 - echograms (hardwalls : Hz - absorbers : Hz) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Modal decay time 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Mode 8 – waveforms (hardwalls : Hz - absorbers : Hz) Mode 8 - echograms (hardwalls : Hz - absorbers : Hz) 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Modal decay time 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping Mode 8 - Hardwalls Mode 8 - Absorbers

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Modal decay time 1/6MT 10 1/3MT 20 1/2MT Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Modal decay time 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Modal decay time 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Peggy Lee «Fever»White Stripes «7 nation army» 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Music rendering HardwallsAbsorbers HardwallsAbsorbers What’s this tune? 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium WaveformsEchograms 10/28/2015 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range Kick drum HardwallsAbsorbers 1. Context2. Electroacoustic absorber3. Realizations4. Room modes damping

Akustisches Kolloquium Conclusions and perspectives 61 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range

Akustisches Kolloquium Conclusions and perspectives 4 electroacoustic absorbers prototypes achieve efficient room mode damping in the reverberant chamber Max damping: Hz, Global damping: 8 dB over [20 – 100 Hz], Max modal decay time reduction: 58 Hz (from 20 s down to 3 s), for a total absorber surface representing only 0.1% of the whole room walls surface 62 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 10/28/2015

Akustisches Kolloquium Conclusions and perspectives Even better performances achieved recently 63 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 10/28/2015 AES Swiss Section / SSA joint meeting dB 70 dB 30 dB 40 dB 65 dB

Akustisches Kolloquium Conclusions and perspectives Even better performances achieved recently The objective performances are under evaluation this week in a more conventional listening room (Goldmund Auditorium) Subjective assessments should also be undertaken (to be done in the coming weeks) 64 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 10/28/2015

Akustisches Kolloquium Conclusions and perspectives New product released by PSI Audio: AVAA (Active Velocity Acoustic Absorber) 65 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 10/28/2015

Akustisches Kolloquium Thank you for your attention This work has been supported by the Swiss Commission for Technology and Innovation (CTI), under the project INTERACTS, agreement number: PFNM-NM. Thanks to : Dr. Sami Karkar Dr. Romain Boulandet Etienne Rivet 66 H. Lissek - Electroacoustic absorption: towards room equalization in the low-frequency range 10/28/2015