Background: There is a notable lack of empirical research on the effects of semi-occluded vocal tract (SOVT) training among choral singers. Existing studies primarily focus on immediate effects and group-level acoustic output, with limited attention to individual voice quality and intervention outcomes.

Objective. This study aimed to investigate the effects of a four-week video-based self-guided intervention using SOVT exercises, either tube phonation in water or humming, on individual voice quality, vocal capacities, and self-perceived vocal function in adult amateur choir singers.

Methods. A randomized controlled trial was conducted with forty-five amateur choir singers (39 women, 6 men, mean age: 49.6 years), randomly assigned to a tube phonation in water group, a humming group, or a control group (practicing breathing exercises without phonation). The intervention was delivered through pre-recorded instructional videos, and thus constituted guided self-training rather than real-time feedback. Multidimensional voice assessments were performed before and after the four-week intervention.

Results. Linear mixed model analyses revealed significant interaction effects for the acoustic parameters jitter, harmonics-to-noise ratio, and the auditory-perceptual parameter roughness, all favoring the tube phonation in water group. Within-group analyses further demonstrated significant post-intervention improvements in the Dysphonia Severity Index and Grade, along with trends toward improvement in the Acoustic Voice Quality Index and the Pathologic Risk Indicators subscale of the Dutch Evaluation of the Ability to Sing Easily within the same tube phonation in water group.

Conclusion. A four-week video-based self-guided tube phonation in water intervention in choir singers led to acoustic, auditory-perceptual and self-perceived voice improvements, indicating its potential as a simple, time-efficient method to reduce pathological voice risk.