a resonator. Human ingenuity has produced various aesthetic-looking and ear-pleasing instruments for musicians to perform. Magical human evolution has also shaped our vocal folds and vocal tract so that we can dynamically change loudness, pitch, and timbre in an instant, in a manner that no other musical instrument can emulate. The fourth part includes electricity and magnetism, room acoustics, digital technology in acoustics, effects of noise on human hearing, and noise regulations for hearing protection that are relevant to sound wave production, transmission, storage, and human ear protection. Our ears are extremely sensitive. Without proper protection, loud noise including loud music can damage our ears. Government regulation and education serve as a first line of protection in working environments. This small book is comprehensible, understandable and enjoyable to all eager students.