Ultrasonic velocities(U), Densities(ρ), Viscosities(η), are measured for three different aromatic carbonyl compounds (Benzaldehyde, Cinnamaldehyde, 4-methoxy benzaldehyde) and Diethylamine in n-hexane solutions containing equimolar concentrations (1x10-4M to 1x10-3M) at 303K. The interaction between solvent molecules and Carbonyl compounds - Diethyl amine complexes are observed. Acoustical parameters such as adiabatic compressibility (k), free length (Lf), internal pressure(pi), cohesive energy(CE), formation constant(K) values are also calculated. These values indicate complex formation and ion-solvent interaction between aromatic carbonyl compounds and diethylamine in n-hexane medium.