Jiaxin Zhong is a postdoctoral researcher in the Graduate Program in Acoustics at The Pennsylvania State University, USA Xiaojun Qiu is a Professor at Nanjing University, China. He is a Fellow of the Audio Engineering Society and the International Institute of Acoustics and Vibration. He is author of An Introduction to Virtual Sound Barriers, and co-author of Active Control of Noise and Vibration, 2nd edition, also published by CRC Press.