STEREOPHONIC PERSONAL AUDIO REPRODUCTION USING PLANARITY CONTROL OPTIMIZATION

1. Paper #558, Session SS28D STEREOPHONIC PERSONAL AUDIO REPRODUCTION USING PLANARITY CONTROL OPTIMIZATION • 15thJuly 2014 Philip Coleman,Philip J. B. Jackson, MarekOlik p.d.coleman@surrey.ac.uk 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)

2. Introduction • Personal sound is an active research topic

3. Introduction • Two main approaches to sound zones [1] • Energy cancellation • Least-squares error minimization • Previous reported results limited to mono • Likely requirement for stereo from consumers • We investigate stereophonic personal audio [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.1929-1940, 2014.

4. Background • Create two virtual loudspeakers and quiet zone • Require control of energy direction Listener in quiet zone undisturbed Target listener gets stereo image

5. Background Zone B Zone A

6. Cost functions • Planarity control (PC)[2] bright zone energy projected in to angular domain [3] constraint on source weights dark zone energy [2] P. Coleman, P. J. B. Jackson, M. Olik, and J. Pedersen, “Optimizing the planarity of sound zones,” in Proc. 52nd AES Int. Conf., Guildford, UK, 2-4 Sept. 2013. [3] Chang, J. H., Choi, J. W., & Kim, Y. H. (2010). A plane wave generation method by wave number domain point focusing. J. Acoust. Soc. Am., 128, 2758.

7. Cost functions • Planarity control (PC) • Steering matrix [4] • Pass-range angles microphones [4] P. J. B. Jackson, F. Jacobsen, P. Coleman and J. Pedersen, “Sound field planarity characterized by superdirectivebeamforming”, in Proc. 21st ICA, Montreal, 2-7 June 2013.

8. Cost functions • Pressure matching (PM; plane-wave target) [5] pressure in the dark zone + bright zone reproduction error • [5] M. Poletti, “An investigation of 2-d multizone surround sound systems”, in Proc.125th AES Conv., San Francisco, CA, 2-5 October 2008.

9. Reproduction setup • 60 channel circular circular array • Two 25 × 35 cm zones • Calculate weights for each frequency (A/B;L/R) • Independent performance measurement set

10. Evaluation • Acoustic contrast • RMSE of energy direction

11. Results • Measured acoustic contrast (both channels)

12. Results • Accuracy of energy placement Left channel Right channel

13. Results • Some higher frequencies have higher RMSE • Some energy at target location • PC left channel 2350 Hz Measured

14. Results • Some higher frequencies have higher RMSE • Some energy at target location • Failure for some grating patterns Free-field simulations, 2350 Hz 120 SPL (dB) PC Right PM Left PC Left 0

15. How does it sound? • Hear for yourself! www.posz.org

16. Results • Results summary • PC gives best contrast • PM gives best accuracy of energy direction • Differing behavior above array aliasing limit

17. Summary • Previous personal audio work in mono • Extension to stereo investigated • Implemented PC and PM on 60 channel circle • PC gave up to 30dB contrast • PC 6 dB greater contrast than PM (freq. ave., 250-2000 Hz) • PM placement 1.2 degrees more accurate (channel & freq. ave., 250-2000 Hz) • Further work should investigate perception

18. Numerical optimization of loudspeaker configuration for sound zone reproduction Interested in personal audio? Paper #219, Session SS06A Stereophonic personal audio reproduction using planarity control optimization

19. Acknowledgements Thanks to Alice Duque who made RIR measurements p.d.coleman@surrey.ac.uk www.linkedin.com/in/philipcolemanaudio