Glottal adduction is a crucial aspect in voice education and vocal performance: it has major effects on phonatory airflow and, consequently, on voice timbre. As the voice is a non-visible musical instrument, controlling it could be facilitated by providing real-time visual feedback of phonatory airflow. Here, we test the usefulness of a flow ball (FB) training device, visualizing, in terms of the height of a polystyrene ball placed in a plastic basket, phonatory airflow during phonation. Audio and electroglottographic recordings of five postgraduate, classically trained singer students were made under three subsequent conditions: before, during, and after phonating into the FB. The calibrated audio signal was inverse-filtered, using an electroglottograph signal to guide the manual tuning of the inverse filters. Mean phonatory airflow, peak-to-peak pulse amplitude, and normalized amplitude quotient were extracted from the resulting flow glottograms. After the FB condition, increases of mean flow and peak-to-peak pulse amplitude were observed in four singers. In addition, the singers' mean normalized amplitude quotient increased significantly. The findings, although exploratory, suggest that reduction of glottal adduction can be observed immediately after FB phonation.