Early psychoacoustics neglected loudness because sound intensity could not yet be controlled.

Evidence

Although the investigations presented above are not exhaustive, these representative studies illustrate that the earliest psychoacoustic work was conducted on the perception of pitch and space. Little evaluation of loudness and its relationship to intensity was conducted. If we pause to consider the environment that these pioneers were working in, we can gain a better understanding of why the early work was conducted in these primary areas. Technology such as sound level meters and earphones had not been developed at that time. While Fechner developed some techniques to measure perception in the mid- 1800s, the devices to manipulate and measure sound levels were not built until the 1920s. Controlling and characterizing the intensity of a sound was even more difficult than manipulating frequency or spatial location. For example, changing the length of strings, altering the properties of materials, or changing size of a tuning fork could manipulate frequency. A Helmholtz resonator or a siren, similar to that developed by Seebeck, could also be used to generate sounds with specific frequencies. On the other hand, techniques at that time did not allow manipulation of intensity without varying the frequency of a sound. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 71

Categorization

• QUESTION: Interesting that frequency and spatial cues were manipulable with simple physics (strings, tuning forks, head shadowing) but intensity was not — worth understanding why decoupled intensity control took until the 1920s.