声道の準狭窄による発声技法の理論と実際

Theory and practice of voice therapy techniques by Semi-Occluded Vocal Tract (SOVT)

　フィンランドでは，1960年代にヘルシンキ大学のSovijärviが，“Resonance tube”と呼ばれる内径8mm，長さ24〜25cm，厚さ1mmのガラス管を用いた音声訓練を提唱し，この訓練法が奏効したことが報告されている．1986年には発声時に声道の一部(開口端)を狭める訓練技法の原理について，主として音響学的な観点から検討され，その後もResonance tube発声技法だけでなく，共鳴強調訓練(Resonant Voice Therapy：RVT)で用いられるレゾナントボイスなどについても検討されるようになった．その結果，この声道の準狭窄(Semi-Occluded Vocal Tract：SOVT)と呼ばれる発声技法は，開口端を狭めることで，声道内の音響インピーダンスを高め，声門流と声帯自励振動に影響することが知られるようになった．SOVT訓練技法は簡便であり音声訓練としての効果も高いことから，近年，急速に報告が増えている．しかしながら，訓練手順や頻度など未解決な点も多く，最終的な結論は出ていない．そこで本稿では，SOVT訓練技法の音響学的原理について概説し，その課題と実際の訓練の留意点を述べたい．

　In Finland, Prof. Sovijärvi of the University of Helsinki proposed a voice therapy technique using a glass tube called a “Resonance tube”, which has an inner diameter of 8 mm, a length of 24-25 cm, and a thickness of 1 mm, and since the 1960s, this method has been reported to be effective in voice therapy. Since 1986, the principles of vocal techniques to narrow a part of the vocal tract during phonation, such as the resonant voice used in Resonant Voice Therapy (RVT), as well as the resonance tube voice therapy, have been investigated mainly from an acoustic viewpoint. As a result, it is now known that this technique, called Semi-Occluded Vocal Tract (SOVT), increases the acoustic impedance in the vocal tract by narrowing the aperture, and affects glottal flow and self-oscillation of vocal fold vibration. The SOVT technique is simple and effective as a voice therapy method, and the number of reports on the SOVT has been increasing rapidly in recent years. However, there are many unresolved issues about SOVT, such as training procedures and frequency of treatment, about which no conclusion has been reached. Therefore, in this paper, I would like to outline the acoustical principles of the SOVT technique and discuss the issues and points for consideration in actual training.