Answer:
This phenomenon is best explained by Weber's Law.
Explanation:
According to Weber's law, the change we are able to perceive in stimuli is proportional to the initial stimuli. Therefore, if the volume was initially high, we would only perceive a change that is also "high". Five decibels aren't much when compared to a high volume. However, when the volume was initially low, five decibels were enough to be perceived.