1/23 Philip Coleman, Philip J. B. Jackson, Marek Olik Centre for Vision, Speech and Signal Processing, University of Surrey, Guildford, Surrey, GU2 7XH, UK Jan Abildgaard Pedersen Bang & Olufsen A/S (now with Dynaudio A/S, Sverigesvej 15, 8660 Skanderborg, DK) 15 th July 2014 Paper #219, Session SS06A

2/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Personal sound is an active research topic

3/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Personal sound is an active research topic A number of control strategies proposed [1] [1] P. Coleman, P. J. B. Jackson, M. Olik, M. Møller, M. Olsen, and J. Pedersen, “Acoustic contrast, planarity and robustness of sound zone methods using a circular loudspeaker array,” J. Acoust. Soc. Am. 135(4), p , 2014.

4/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Loudspeaker arrays for personal audio: -Compact line array [e.g. 2,3] [2] J.-H. Chang, C.-H. Lee, J.-Y. Park, and Y.-H. Kim, “A realization of sound focused personal audio system using acoustic contrast control,” J. Acoust. Soc. Am. 125(4), p. 2091–2097, 2009 [3] Simón-Gálvez, M. F., Elliott, S. J., & Cheer, J. “The effect of reverberation on personal audio devices.” J. Acoust. Soc. Am. 135(5), , 2014.

5/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Loudspeaker arrays for personal audio: -Compact line array -Circular array [e.g. 4,5] [4] F. Jacobsen, M. Olsen, M. Møller, and F. Agerkvist, “A comparison of two strategies for generating sound zones in a room,” in Proc. 18 th ICSV, Rio de Janeiro, Brazil, July [5] M. Shin, S. Q. Lee, F. M. Fazi, P. A. Nelson, D. Kim, S. Wang, K. H. Park, and J. Seo (2010), “Maximization of acoustic energy difference between two spaces,”. Acoust. Soc. Am. 128(1), p , 2010

6/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Loudspeaker arrays for personal audio: -Compact line array -Circular array Both array types may have benefits Users may have some freedom to position loudspeakers We investigate optimal loudspeaker placement

7/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Best positions for N loudspeakers ? Can optimized arrays give… -Improved cancellation? -Better control of target sound field? -Reduced power consumption? -Increased robustness? -Improved compensation for room?

8/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Previous work -Crosstalk cancellation [6,7] -Sound zones [8] [6] M. R. Bai, C.-W. Tung, and C.-C. Lee, “Optimal design of loudspeaker arrays for robust cross-talk cancellation using the taguchi method and the genetic algorithm,” J. Acoust. Soc. Am. 117(5), p. 2802–2813, 2005 [7] T. Takeuchi and P. A. Nelson, “Optimal source distribution for binaural synthesis over loudspeakers”, J. Acoust. Soc. Am. 112(6), p. 2786–2797, 2002 [8] P. Coleman, M. Møller, M. Olsen, M. Olik, P. J. B. Jackson, and J. Pedersen (Abstract), “Performance of optimized sound field control techniques in simulated and real acoustic environments,” in J. Acoust. Soc. Am., 131(4), p. 3465, Presented at Acoustics 2012, Hong Kong, May 2012, available via

9/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Sound zone source weights calculated with acoustic contrast control [9,10] constraint on source weights dark zone energy bright zone energy [9] J-W. Choi and Y-H Kim, “Generation of an acoustically bright zone with an illuminated region using multiple sources”, J. Acoust. Soc. Am. 111, 1695–1700, [10] Elliott, S. J., Cheer, J., Choi, J. W., & Kim, Y. Robustness and regularization of personal audio systems. IEEE Trans. ASLP, 20(7), , 2012.

10/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Generalizable set of metrics Evaluation metricLinked characteristics ContrastMinimal interference Planarity [11]Spatial sound distribution Control effortRobustness, low electrical power [11] P. J. B. Jackson, F. Jacobsen, P. Coleman and J. Pedersen, “Sound field planarity characterized by superdirective beamforming”, in Proc. 21st ICA, Montreal, 2-7 June 2013.

11/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Evaluation metricLinked characteristics ContrastMinimal interference PlanaritySpatial sound distribution Control effortRobustness, low electrical power observed sound pressures in zone A observed sound pressures in zone B number of observation microphones in zone B number of observation microphones in zone A Generalizable set of metrics

12/23 Numerical optimization of loudspeaker configuration for sound zone reproduction energy coincident with the principal plane wave direction total energy in the zone Evaluation metricLinked characteristics ContrastMinimal interference PlanaritySpatial sound distribution Control effortRobustness, low electrical power Generalizable set of metrics

13/23 Numerical optimization of loudspeaker configuration for sound zone reproduction sum of squared loudspeaker weights reference loudspeaker weight Evaluation metricLinked characteristics ContrastMinimal interference PlanaritySpatial sound distribution Control effortRobustness, low electrical power Generalizable set of metrics

14/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Defined optimization cost function based on physical metrics -Where Choose or optimize weighting coefficients Could use perceptual model [12] [12] J. Francombe, P. Coleman, M. Olik, K. Baykaner, P. J. B. Jackson, R. Mason, M. Dewhirst, S Bech and J. Pedersen, "Perceptually optimized loudspeaker selection for the creation of personal sound zones, in Proc. 52nd AES Int. Conf., Guildford, UK, 2-4 Sept

15/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Sequential Forward-Backward Search [13] -+2, -1 Applied each element in turn Focus here on contrast-only case -Other results included in paper -Selected between 6 and 30 optimal positions -based on predicted performance (mean at 100, 200,..., 4000 Hz for both zones) [13] P. A. Devijver and J. Kittler (1982), Pattern recognition: A statistical approach. Englewood Cliffs, NJ: Prentice/Hall International., p.220

16/23 Numerical optimization of loudspeaker configuration for sound zone reproduction 60 channel circular candidate array Two 25 × 35 cm zones Independent performance measurement set

17/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Array configurations -10 loudspeaker example Contrast-onlyArc Circle

18/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Acoustic contrast (average over freq.) -Circle worst over frequency -Optimal set best for 6 loudspeakers Contrast-only

19/23 Numerical optimization of loudspeaker configuration for sound zone reproduction 10 loudspeakers over frequency Contrast-only 6 dB

20/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Sound pressure level Hz notch, simulated in free-field Contrast-only Dark zone Bright zone

21/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Loudspeaker array geometries not previously investigated for sound zones Proposed objective function based on physical metrics Improved min. contrast by 6 dB compared to reference arrays (10 loudspeaker example) Further work should investigate: -Weighting of cost function -Extended loudspeaker sets -Advanced numerical search methods

22/23 Paper #558 Did you see my last talk? Numerical optimization of loudspeaker configuration for sound zone reproduction

23/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Thanks to Alice Duque who made RIR measurements

24/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Optimal 10 channel arrays for other weights: Contrast-onlyEffort-onlyCondition-onlyPlanarity-only

25/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Optimal 10 channel arrays: Contrast-onlyEffort-only Cond-only Planarity-only

26/23 Numerical optimization of loudspeaker configuration for sound zone reproduction Measure room responses (60 × 768) Select optimal loudspeakers Calculate optimal source weights for each frequency Inverse FFT/shift to make FIR filters (×60) Independent performance measurement set