Sound level convention defaults to pressure level because it is measurable and matches hearing.

Evidence

These different means of describing and measuring sound amplitudes can be confusing and one must be careful to ascertain which one is being used in a given context. In general, a reference to sound level implies that the SPL is being used because the pressure component can be measured easily and corresponds most closely to what we hear. — David Howard, Jamie Angus, coustics and Psychoacoustics, 198

Categorization

Category: Definitional Content

• DEFINE: Establishes the default meaning of ‘sound level’ as SPL — a useful disambiguation convention.
• QUESTION: Worth chasing: does SPL correspond most closely to what we hear in all frequency ranges, or only at certain frequencies?

Related

• Reported sound levels almost always refer to pressure, matching human hearing (similarity 0.96)
• Sound pressure level is the standard because it matches hearing (similarity 0.90)
• Sound level meters measure pressure, from which intensity is derived (similarity 0.84)
• Sound intensity level and sound pressure level are roughly equivalent (similarity 0.83)
• ‘Sound level’ is a deliberately vague unit-free term for sound size (similarity 0.83)
• Sound amplitude is measured as root mean square pressure because ears sense pressure (similarity 0.83)
• Negative SPL readings indicate levels below the reference threshold. (similarity 0.82)
• Sound pressure level depends on oscillation amplitude, not average pressure (similarity 0.82)
• Sound pressure level and intensity level coincide only without reflecting surfaces (similarity 0.82)
• Speaker sensitivity gives SPL at one meter per watt of power input. (similarity 0.81)
• Sensation level expresses tone level relative to one individual’s own threshold (similarity 0.81)
• Sound audibility depends on both its level and its frequency (similarity 0.81)
• Objective sound amplitude measures do not describe perceived loudness. (similarity 0.80)
• Sound pressure and intensity are distinct quantities interconvertible by a known relationship (similarity 0.80)
• SIL and SPL always change in proportion even where their absolute values differ (similarity 0.80)