sonic devices working as coherent multifrequency adiabatic splitters, phase difference analyzers and coherent multifrequency adiabatic couplers. In particular, we will investigate the sound propagation in systems of two linear defects in sonic crystals (SCs).[@martinez-sala_sound_1995; @sanchez-perez_sound_1998] SCs are a particular case of PCs that consist of solid scatterers embedded in a fluid host medium. SCs permit considering the propagation of only longitudinal waves, which constitutes an important simplification. Furthermore, SCs are experimentally relevant since, for example, they allow for measurements inside the crystal.[@romero-garcia_angular_2013]

This paper is organized as follows. In Section \[sc\_sectionSC\] we will present the considered physical system consisting of two coupled linear defects in a SC, and we will calculate the allowed bands into the band gap and their corresponding supermodes. We will also distinguish between two different frequency ranges inside the band gap, one where two supermodes coexist, and another range with only one supermode available. In Section \[sc\_twosmode\], for the frequency range in which both supermodes exist, we will study spatial adiabatic passage processes through the coupled-mode equations, and we will design a coherent multifrequency adiabatic splitter, in Subsection \[sc\_CMAS\], and a phase difference analyzer, in Subsection \[sc\_PDA\]. In Section \[sc\_onesmode\], we will focus on the frequency 