Abstract: In this paper, an improved theory for determining cigenfrequencis of flute is demonstrated. The theory is developed from author's previous work in order that it can be applied as well as to analyse the flute of a new type, such as the so-called 'aligned double flute'. The acoustic character of the double flute is analysed rigorously. The procedure to calculate the correction of the effective length of the tube at exit terminal is investigated. Theoretical formulas to determine eigenfrequencies of the double flute are derived. Correction at blow aperture and the influence of temperature deviation caused by the warm blow are discussed.
Two typical structures of the double flute are illustrated. It is shown that experimental results are in good agreement with the theoretical calculation. It shows that the theory proposed in the present paper is delicate and reliable. It can serve as a theoretical fundamental for design or manufacture of the double flute in practice