Acceptability and Implementation Considerations for a 40-Hz Sine-Wave–Integrated Soundscape Intervention: A Qualitative Exploratory Study

Background/Objectives: 40-Hz sensory stimulation is being explored as an everyday, non-pharmacological approach for cognitive-health applications, but sustained use depends on acceptability and implementable delivery/UX. We examined user-perceived acceptability and implementation considerations for a 40-Hz sine-wave–integrated soundscape intervention. Methods: Eleven adults aged ≥40 years in Seoul, Republic of Korea were assigned to waves or forest soundscapes (between-participants) and completed a within-participant comparison of 40-Hz–OFF (soundscape-only) versus 40-Hz–ON (soundscape plus an additively layered 40-Hz sine wave). Each condition comprised seven cycles of 50 s playback and 10 s silence (~7 min) with a 10 min washout. Participants completed a session-end 7-point Likert appraisal of the 40-Hz–ON stimulus and a semi-structured interview. Interview transcripts were analyzed using thematic analysis and interpreted using the Theoretical Framework of Acceptability and Proctor et al.’s implementation outcomes as sensitizing frameworks. Results: Likert appraisals indicated mid-to-high comfort and immersion (medians = 5) and moderate calmness (median = 4), with relatively low unpleasantness (median = 2). Perceived artificiality varied widely (range 1–7) and overall preference was moderate (median = 4). Interviews showed heterogeneous detectability of 40-Hz inclusion; acceptability depended on whether the layered component blended naturally or was perceived as mechanical/rumbling. Participants highlighted context fit (e.g., bedtime versus morning routines), “backgroundability,” and low-friction automation (timers/scheduling) as key sustainability factors, while emphasizing acoustic safeguards such as gentle onset and conservative default levels. Conclusions: A 40-Hz sine-wave–integrated soundscape can be acceptable, but responses are heterogeneous and sensitive to timbral salience and usage context. Scalable delivery should incorporate space-oriented playback options, simplified automation, acoustic safeguards, and coherence-focused guidance with appropriate disclaimers.