1) How do you add two different decibel levels? For example, 65 dB + 80 dB
? 145 dB. Must you convert it to intensity first? delta B = 10log(80/65) =
0.9, and so the answer is 65.9 dB?
2) If a car sounds a horn. If you hear 450 Hz as it approaches and 350 Hz
as it recedes, the actual frequency is about 394 Hz (not 400 Hz).
Conceptually, why isn't the Doppler effect result symmetric for when the
sound (or observer) is approaching/receding the observer (sound)?
3) All musical instruments produce overtones (harmonics) except tuning
forks and some electronic pianos. How can the human vocal chords produce
pure tones? Living things are both delicate and complex, yet it is easy to
sing into a microphone and see a nice sine wave on an oscilloscope.