Final answer:
The term that defines the measurement of sound pressure (dB SPL) over the frequency spectrum where the listener perceives a constant loudness with pure steady tones is Equal Loudness Level (ELL).
Step-by-step explanation:
The term that defines the measurement of sound pressure (dB SPL) over the frequency spectrum where the listener perceives a constant loudness with pure steady tones is Equal Loudness Level (ELL). The Equal Loudness Level curve, also known as the Fletcher-Munson curve, shows the sound pressure levels at different frequencies that are perceived as equally loud to the human ear.