For understanding the sound production of flue organ pipes, the acoustic properties of the two main components, the acoustic resonator and the air jet generator at the labium (flue + upper lip), have been investigated separately. It was found that the formant structure of the stationary sound spectrum is mostly determined by the geometry of the pipe, including the location, size, and shape of the openings (mouth and open end), while the attack is strongly influenced by the air jet generator. An influence of the wall vibrations on the stationary sound has been also found, but this effect could be neglected until the wall is not too thin. The spectra of the stationary sound radiated by the openings are markedly different. The analysis of their formant structures implies that the source of the radiation is the acoustic flow at the openings. Experiments performed on labium models and pipes with damped acoustic resonators show that an edge tone with characteristic spectrum appears first during the attack. Its sound field may excite the acoustic resonator purely acoustically, preceding the development of the coupling between jet and acoustic oscillations. This assumption has been supported by the experiments discussed in the paper.