1) Acoustics refers to vibrations that are audible to humans, ranging from 20-20,000 Hertz. All sounds originate from object vibrations. 2) Key characteristics of sound include requiring a medium to propagate, having a finite velocity, and traveling at different speeds in different materials. Sounds can be classified by pitch, timbre, and intensity. 3) Important factors that affect building acoustics include optimizing reverberation time, avoiding uneven loudness or focusing due to interference or resonance, and reducing echoes and noise. Absorbing materials and proper ventilation help address these factors.