Determination of directional echograms and application in room acoustics

Transcription

1 Determination of directional echograms and application in room acoustics J.J. Embrechts, N. Werner and F. Duthoit Laboratory of Acoustics (Institut Montefiore ULg) 28/2/2007 ABAV Brugge

2 Echogram : definition listener source A diagram showing the distribution of the acoustical energy at the receiver, as a function of time arrival. (whatever the direction of incidence) 28/2/2007 ABAV Brugge

3 Echogram : applications in room acoustics Room acoustics parameters : -T30, EDT - SPL -C80, D50 - auralization Room impulse response 28/2/2007 ABAV Brugge

4 Directional Echogram : definition Z θ directional echogram dω Y X ϕ hsr ( θ, φ, t) dω A diagram showing the distribution of the acoustical energy at the receiver, as a function of time arrival, in a particular direction of incidence. 28/2/2007 ABAV Brugge

5 Directional echogram : computation Z 67 5 θ dω source listener X ϕ Y The directional echograms are evaluated by ray-tracing, at each listener s position. The 3D space around the listener s head is divided into 26 solid angles, simulating 26 directional microphones. 28/2/2007 ABAV Brugge

6 Directional echograms : computation in two «academic» room acoustics problems 28/2/2007 ABAV Brugge

7 Example 1 : Room A (ref. Hodgson, JASA, 89(2), 1991) Z Y Source X Cubic room -side length : 27.5m -absorption coefficient of all faces : scattering coefficient of all faces : d=0 or d=1 28/2/2007 ABAV Brugge

8 direct sound S R d=1 Room A : Directional echograms at one receiver position, 5m away from the source, diffusing surfaces. 28/2/2007 ABAV Brugge

9 direct sound S R d=0 Room A : Directional echograms at one receiver position, 5m away from the source, specular surfaces. 28/2/2007 ABAV Brugge

10 direct direct S R d=0 S R d=1 Room A : Directional echograms at one receiver position, 5m away from the source. 28/2/2007 ABAV Brugge

11 Example 2 : Room B (ref. Hodgson, JASA, 89(2), 1991) Z Y Source X Long disproportionate room -55m x 110m x 5.5m -absorption coefficient of all faces : scattering coefficient : d=0 or d=1 28/2/2007 ABAV Brugge

12 direct sound S R d=1 T30=4.3s Room B : Directional echograms at one receiver position, 5m away from the source, diffusing surfaces. 28/2/2007 ABAV Brugge

13 direct sound d=0 S R T30=16.4s Room B : Directional echograms at one receiver position, 5m away from the source, specular surfaces. 28/2/2007 ABAV Brugge

14 direct direct d=0 S R S R d=1 T30=16.4s T30=4.3s Room B : Directional echograms at one receiver position, 5m away from the source. 28/2/2007 ABAV Brugge

15 d=0 d=1 S R S R T30=16.4s T30=4.3s Room B : Energy decay curve at one receiver position, 5m away from the source. 28/2/2007 ABAV Brugge

16 S R S R d=0 d=1 Room B : T30 directional at one receiver position, 5m away from the source. 28/2/2007 ABAV Brugge

17 Conclusion of the analysis of two «academic» problems The directional echograms can afford interesting additional information, especially for : -disproportionate rooms, -weak diffusing surfaces, -asymmetrical distribution of acoustical absorption. 28/2/2007 ABAV Brugge

18 Directional echograms : application in a room acoustics project 28/2/2007 ABAV Brugge

19 Project : Renovation of an ancient horseriding school into a cultural polyvalent hall. Théâtre du Grand Manège (Namur) 28/2/2007 ABAV Brugge

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22 Project : Room B (ref. Hodgson, JASA) Z Y Source X absorbing roof Long disproportionate room -55m x 110m x 5.5m -absorption coefficient of all faces : scattering coefficient : d=0 or d=1 Seats reflecting walls 28/2/2007 ABAV Brugge

23 R S EDT=1.4s T30 = 5.6s Polyvalent hall, original situation : Echogram and energy decay curve at one receiver position. 28/2/2007 ABAV Brugge

24 R S Polyvalent hall, original situation : Directional echograms at one receiver position, 1 khz. 28/2/2007 ABAV Brugge

25 R S Polyvalent hall, original situation : Directional energy decays at one receiver position, 1 khz. 28/2/2007 ABAV Brugge

26 R S R S Polyvalent hall, original situation : Directional T30 at two receiver positions, 1 khz. 28/2/2007 ABAV Brugge

27 Project : Théâtre du Grand Manège (Namur) Renovation of an ancient horse-riding school into a cultural First polyvalent acoustical treatment hall. : Absorbent and diffusing surfaces on the left wall (when looking from the scene) 28/2/2007 ABAV Brugge

28 R S Polyvalent hall, first acoustical treatment : Directional echograms at one receiver position, 1 khz. 28/2/2007 ABAV Brugge

29 R R S S before treatment : T30=5.6s after treatment : T30=1.9s Polyvalent hall: Directional energy decays at one receiver position, 1 khz. 28/2/2007 ABAV Brugge

30 Théâtre du Grand Manège (Namur) Horizontal audience surface 28/2/2007 ABAV Brugge

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32 R S EDT= 2.3s T30 = 6.2s Polyvalent hall, horizontal audience surface : Echogram and energy decay curve at one receiver position. 28/2/2007 ABAV Brugge

33 R R S S tilted audience surface : T30=1.9s horizontal audience : T30=6.2s Polyvalent hall, horizontal audience surface : Directional energy decays at one receiver position, 1 khz. 28/2/2007 ABAV Brugge

34 Conclusions -Directional echograms can give original information in non-diffuse acoustical fields. -They are particularly useful in the detection of potential flutter echos, lack of diffusivity and asymmetrical distribution of absorption. - They can explain significant differences between T30 and EDT, as a result of nonlinear energy decays. - They can suggest optimal placement of absorbent and/or diffusing material to attenuate reverberation. 28/2/2007 ABAV Brugge