The document discusses decibels and how they are used to measure sound intensity levels relative to a reference level of 1000Hz. It provides the formula for calculating sound intensity level in decibels and uses it to solve a sample problem comparing the sound intensity of a library to a bedroom. The key points are: - Decibels provide a logarithmic scale to compare sound intensities to a reference level - The reference level for sound is 1000Hz - The formula is used to determine if a student's estimate of a 7 times difference in sound intensities between a library and bedroom matches the given 10dB intensity level difference. It is determined that the student is wrong since 10dB corresponds to a 10 times, not 7 times