Answer
a. No.
b. Yes.
c. Yes.
d. No.
Work Step by Step
a. A sound level of zero dB corresponds to the threshold of hearing at 1000 Hz; there is still sound.
b. Equation 16.15 makes sense for negative sound levels. A negative sound level can be assigned to a sound that is weaker (i.e., has less intensity) than a sound with a sound level of 0 dB.
c. If there is zero intensity, the displacement amplitude is zero, and there is no sound.
d. One cannot have less sound than no sound.