Discontinuity of the second formant (F2 discontinuity) is often found during back-to-front vowel transitions, and it has been thought due to two possible effects: acoustic coupling with the subglottal tract (subglottal-coupling effect, SCE) and traveling anti-resonance of the interdental space (interdental-space effect, ISE). Although both are possible to appear together, either of the two is common to find in many spectrographic observations, and how to distinguish from one another is often puzzling. This study aims at exploring manifestations of the two effects in Chinese triphthongs through acoustic analysis on front-to-back vowel sequences. Test utterances were recorded from five Chinese speakers with simultaneous measurement of subglottal resonance via a vibration sensor adhered to their necks. Results revealed that F2 discontinuity occurs near the second subglottal formant (SgF2) but not always, and discontinuity of both F2 and F3 is more common that occurs with a short time lag, suggesting predominance of ISE rather than SCE in the data.