The conception of a true line source encounters a lot of technical problems the designer has to solve. The main one is the fusion of all individual sources in only one virtual line source in order to generate on all the frequency range a perfect free of lobbing effects toroidal wavefront. If the solution is evident for low frequencies, this is not the same piece of cake for high ones. The acoustical size of a sound source is close to the wavelength of the generated signal. At 100Hz, the wavelength is 3.4m, so, two speakers distant of 1.2m (half the wavelength) create a perfect coherent source. At 1kHz, the wavelength is only 34cm and these two speakers are no more a coherent source and generate interferences. At 10kHz, the wavelength is 3.4cm and there are no speakers able to realize the performance to be smaller than 1.7cm in the real professional sound reinforcement world. The solution to this problem was found in the year 1982 by a French scientist, Dr Christian Heil, who build the first cylindrical sound wave driver (DOSC) and the first true line source system.
Many improvements have been made in line source technology, but the physical laws remain the same.