(1) The design and electroacoustic simulation of headphones (or earphones) (2) Flat panel experiments. Mark Kahrs

Transcription

1 (1) The design and electroacoustic simulation of headphones (or earphones) (2) Flat panel experiments Mark Kahrs 1

2 Part (1) 1. Introduction 2. Headphones/earphones 3. Perceptual aspects 4. Design and Simulation with SPICE 5. Conclusion 2

3 Introduction - Why headphones? 1. Incredibly popular! (fan sites, etc) 2. Design is arcane 3. Few papers in open literature 4. Acoustic design + DSP = opportunity 3

4 External ear anatomy 4

5 Perception Freq. resp. is not flat not that phase sensitive HRTFs differ individually ILDs must not change 5

6 Headphones and earphones 1. Circum-aural (around) 2. Supra-aural (over) 3. Supra-concha 4. Intra-concha 5. Insert 6

7 Drive mechanisms Electrodynamic - armature, isodynamic, dynamic Electrostatic - electret, condensor Piezoelectric (old style) 7

8 Electrodynamic drives Heavier (coil weight) Larger displacement Compliance controlled - not mass Basic types: 1. Armature (easy to miniaturise) 2. Isodynamic(Ortho) or Dynamic 8

9 Electrostatic & Piezoelectric drives Condensor - Sennheiser Orpheus, Stax (HV needed) Electret - Pre-polarized (AKG-340) Piezoelectric - Pre WWII, Pioneer SE-700 9

10 Headphone design aspects Acoustical design: Closed or open? Equalisation? Electro-mechanical design: Drive choice 10

11 Strategy (reprise) Describe each domain with R,L,Cs Interconnect with controlled sources Insert meters at interesting points Label with node numbers Perform transient, AC analyses 11

12 Analysis strategy: (reprise) All volumes become acoustic compliances (C) with one terminal grounded Connect compliances with pipes (L) and resistors (R) Leaks are resistors (R) to ground Outside enclosure is radiated to radiation impedance 12

13 Simulation of IEC IEC711 test IEC711 is the standard coupler model Available from B&K in mechanical form 13

14 Modeling the loudspeaker R E L E L m C m Rm Z AF V S + Blv + Bli SP D + P D Z AB Force factor = Bli Back emf = Blv Diaphragm area = S D 14

15 Circum-Aural Oldest style Most comfortable (but heaviest) Best isolation (used for ANC) Open or closed in back 15

16 Design details Cushion - has compliance (and leaks) Transducer - size, weight, manufacturability Frequency response - equalisation (compensation) for resonances 16

17 Circumaural [JVC] Shown with electrodynamic driver Diaphragm (32) Voice coil (35) Damping material (23) 17

18 Supra aural (Bose, ANC) driver (40) microphone (42) resistive mesh (54) 18

19 AKG An iconic circumaural Passive diaphragms (5) Adds restoring force and mechanical resistance 19

20 AKG-250 circuit RL (B) - Leak behind transducer RL (3) - Mesh behind transducer C123 - Cavity compliances behind diaphram C0 - Ear transducer compliance RLC (bb) - Cushion RLC (pm) - Passive membranes RL (0) - Cushion leak Z AL - Loads 20

21 AKG-250 circuit RZ BAL RC B123 C 0 R bb R pm R 0 Z AL 21

22 Simulation of AKG-250 (with IEC711) Without passive membranes With passive membranes Parameters are given by designer (Poldy) Addition of passive membranes flattens out response 22

23 Isodynamic construction Permanent magnets (26, 26 ) Diaphragms (32, 34) 23

24 Isodynamic circuit (open supraaural) RL (R) - Radiation resistance (Bauer model) RH - Mesh behind transducer C1 - Cavity compliances behind diaphram C0 - Ear transducer compliance RLC (bb) - Cushion (ignored) RL (0) - Cushion leak Z AL - Loads 24

25 Isodynamic circuit R H R 0 Z AL C 1 C 0 Z AL 25

26 Isodynamic simulation AKG isodynamic Very linear (but not at the ear) 26

27 Supra concha earphone The most common headphone Model all leaks Fortunately, parameters are available 27

28 Supra concha circuit Holes - Subcircuit for hole openings (15*RL) RL (back) - Back opening C2 - Cavity compliances behind diaphram C7 - Ear transducer compliance RLC (9) - Foam RL (8) - Leak Z AL - Loads 28

29 Supra concha circuit R back Holes R 8 C 9R0 Z AL C 2 C 7 ZAL 29

30 Supra concha simulation Tikanders concha model All leaks modelled Note resonances 30

31 Conclusions SPICE simulation can be used to check headphone design But... nonlinear aspects are not simulated Simulation also includes ear model Parameters for existing headphones/earphones are difficult to obtain 31

32 Part (2) Flat Panel Experiments 1. Introduction 2. Transducers 3. Experiments 4. The future 32

33 Introduction: Flat panels Used sparingly in orchestral music (Wagner) Plate reverb 33

34 Acoustics (from Fletcher & Rossing) Can be: free, clamped or simpled supported f mn = 0.453c L h(( m+1 L x ) 2 + ( m+1 L y ) 2 ) c L = E ρ(1 ν 2 ) ν 0.3 (Poisson s ratio) E (Young s modulus) ρ (density) 34

35 Transducers Different from loudspeakers (no cone) Bought from boutique German speaker manufacturer (ELAC) 15 watt max, heat cutoff Affixed with adhesive (what kind?) 35

36 Experiments 1. Steel panel, removable glue 2. (thinner) Brass panel, removable glue 3. Brass panel, epoxy 36

37 The future... Speckle inferometry? Artist installation? Feedback system? 37

38 Particular thanks to... Stefan Murray David 38

39 The End. 39