<p>Conventional noise control strategies that rely primarily on reducing acoustic energy often face practical limitations in real-world environments. The audio injection method (AIM) offers an alternative, sound quality-oriented approach by superimposing controllable, positive sounds to mitigate annoyance. Because the superimposed sound is perceptually more complex than the original noise alone, annoyance under AIM is expected to be shaped not only by acoustic exposure but also by non-acoustic factors. Consistent with the growing emphasis on such factors in ISO/TS 16755-1:2025, this study investigates the key non-acoustic factors of short-term annoyance for superimposed sounds in AIM contexts. A quasi-field online questionnaire survey was conducted, recruiting 304 participants. Potential components related to non-acoustic factors were identified and refined using exploratory factor analysis (EFA), and a path-based structural model was then used to quantify direct and indirect effects on annoyance. The results show that: (1) AIM can effectively reduce reported annoyance across multiple noise scenarios; (2) noise sensitivity adversely influences attitudes toward the original noise source, thereby increasing original noise annoyance; (3) original noise annoyance significantly predicts annoyance of the superimposed sound; and (4) more than half of participants expressed acceptance of AIM, and positive attitudes toward AIM together with preference for controllable sounds are associated with lower superimposed-sound annoyance. These findings provide a mechanism-based, interpretable framework for incorporating non-acoustic factors into the design and evaluation of AIM-type interventions in environmental and architectural acoustics.</p>