Accurate sound reproduction from two loudspeakers in a living room

Transcription

1 Accurate sound reproduction from two loudspeakers in a living room Siegfried Linkwitz 13-Apr-08 (1)

2 D M A B Visual Scene 13-Apr-08 (2)

3 What object is this? 19-Apr-08 (3)

4 Perception of sound 13-Apr-08 (4)

5 The Ear-Brain-Processor Sound stream segregation & integration using sound onset, timbre, duration, envelope, loudness, direction cues Precedence effect Head movement, HRTF Our perceptual acoustic horizon is variable and adapts by attention 13-Apr-08 (5)

6 Association Model of Perception Guenther Theile in Perception of Reproduced Sound, May-08 (6)

7 Visual & Auditory Scene 13-Apr-08 (7)

8 Accurate sound reproduction = creating an auditory illusion of the original auditory scene 13-Apr-08 (8)

9 Misleading auditory cues in Playback and Recording must be minimized to strengthen the illusion of Being There 13-Apr-08 (9)

10 Misleading cues from the loudspeaker On-axis frequency response variations Frequency dependent directivity Resonances / stored energy Non-linear distortion Cabinet edge diffraction 13-Apr-08 (10)

11 Potentially misleading cues from the room Low frequency modes / resonances Reverberation / RT60 Reflections Left-Right setup symmetry 13-Apr-08 (11)

12 The room becomes engaged in the reproduction of an auditory scene via the directional behavior of the loudspeakers 13-Apr-08 (12)

13 D M A B Measurement & listening room 13-Apr-08 (13)

14 Two types of loudspeakers 13-Apr-08 (14)

15 Room-Loudspeaker-Listener layout 13-Apr-08 (15)

16 Left speaker Room response at A Right speaker Dipole Dipole Monopole Monopole from 200 ms impulse response time record 13-Apr-08 (16)

17 Room reflections and their measurement Tone burst test signal 13-Apr-08 (17)

18 3 khz burst response at A during 50 ms 13-Apr-08 (18)

19 Power spectrum during 50 ms of 3 khz burst 13-Apr-08 (19)

20 3 khz burst with room reflections R 200 ms 13-Apr-08 (20)

21 OBSERVATION The dipolar and monopolar loudspeakers sound almost identical in spectral balance and clarity despite their differences in measured room response and burst response. Phantom imaging is very similar, precise, but with greater depth for the dipole. Loudspeakers and room disappear 13-Apr-08 (21)

22 POSTULATE To minimize misleading cues from the room requires: Spectrum of reflections = direct sound Delay of reflections >6 ms ( l > 6 ft) Symmetry of reflections rel. to direct sounds 13-Apr-08 (22)

23 Loudspeaker requirements Frequency-independent polar response Omni-directional Bi-directional, dipolar Uni-directional, cardioid Consistent acoustic illumination of the room at all frequencies 13-Apr-08 (23)

24 Room requirements Symmetrical loudspeaker-listener setup Loudspeakers >3 ft from large surfaces Frequency-independent absorption/diffusion 13-Apr-08 (24)

25 THE PRECEDENCE EFFECT IN A ROOM Localization Direct and reflected sound are heard as a single entity from the location of the direct sound. The Haas effect Integration of a direct sound with a delayed sound adding loudness De-reverberation We are not normally much aware of reverberated sound even when its energy is larger than that of the direct sound William M. Hartmann, Apr-08 (25)

26 Precedence Effect Parmly Hearing Institute 13-Apr-08 (26)

27 Clifton Effect Parmly Hearing Institute 13-Apr-08 (27)

28 Franssen Effect Effect with 1 khz tone Effect with noise 1 khz L&R 13-Apr-08 (28)

29 EVOLUTION OF SPATIAL HEARING Adaptation to the different acoustic properties of forest and savanna Survival by attention to cues for direction and distance of a threat Ignoring stationary, non-threatening sounds Adaptation to listening in modern closed spaces 13-Apr-08 (29)

30 Auditory Scene Recording ORTF+A 13-Apr-08 (30)

31 Impediments to recreating an auditory scene Inadequate polar response of typical box loudspeakers Loudspeaker placement too close to and non-symmetrical to the room walls Room treatment with absorbers and diffusers which change the spectral content of reflections Electronic room equalization above bass frequencies Insufficient dynamic range of the loudspeaker Recordings with too many microphones and in separated acoustic spaces. Clothes line recordings 13-Apr-08 (31)

32 Two-channel Stereo vs. Surround sound What am I missing? Complete Envelopment What am I gaining? Believability Satisfaction Simplicity 13-Apr-08 (32)

33 Two-channel playback in a normal living space can provide an experience that is fully satisfying. Loudspeakers and room disappear and the illusion of listening into a different space takes over. 13-Apr-08 (33)

34 Thank you for your attention Questions? 13-Apr-08 (34)