Relationship between transient sound and mouth tone in flue organ pipe

Mouth tone has been investigated to study the transient sound of flue organ pipes. Mouth tone is a sound which is emitted from a pipe when its resonator is filled with an acoustic absorber. The mouth tone sounds like a broad band noise, however, it has also a certain pitch. In its frequency spectrum some peaks are present and the frequency of the largest peak is very close to the frequency of the harmonic which builds up fastest of all the harmonics of the normal pipe sound. This observation could be explained by the fact that the jet driven system around the mouth produces the mouth tone in a much shorter time than the time needed for the excitation of the pipe resonator. On the other hand, the characteristics of the mouth tone have rarely been investigated so far. To clear up the factors through which the frequency characteristics of the mouth tone can be determined, the peak frequencies of the mouth tone were compared to the frequencies of the edge tone which were calculated from the jet velocity using Brown's equation. The change in the 5th mode of the mouth tone was very similar to that in the 3rd mode of edge tone. This suggests that the 5th mode of the mouth tone is caused by the 3rd mode of edge tone. It was also proved that the peak frequencies except for the 1st peak depend on the blowing pressure, i.e. on jet velocity.