At what threshold does sound become painful?

The correct threshold at which sound becomes painful typically falls within the range of 130-140 dB SPL (Sound Pressure Level). This is the level where sound can cause physical discomfort or pain, which is often referred to as the "threshold of pain."

In comparison to the other options, while 110-120 dB HL (Hearing Level) is notably high, it is still below the pain threshold for most individuals. The decibel levels expressed in dB SPL are more directly related to the intensity of sound pressure that can be perceived as painful.

Furthermore, thresholds indicated in the range of 70-80 dB or 90-100 dB, while they may be uncomfortable to some, do not typically reach the point of causing pain. The pain threshold is distinct from discomfort levels and is consistently higher, which explains why the other choices do not accurately represent when sound becomes painful.