Density (ρ) and ultrasonic speed (u) in the mixtures of isopropanol(IPA), isobutanol(IBA) and isoamyl alcohol(IAA) with equimolar mixture of ethanol and formamide (EMM), including those of pure liquids have been measured over the entire range of composition at temperature 308.15K. From these experimental values, the deviations in ultrasonic speed (Δu) and isentropic compressibility (Δks), excess acoustic impedance (ZE) and excess free length ( E f L ) have been calculated and reported. The variations of these properties with composition of solution are discussed in terms of molecular interactions between unlike molecules of the mixtures. Further more, the experimental values of u for afore mentioned mixtures have been compared with theoretically estimated ultrasonic speeds using different empirical relations and the relative merits of these theories and relations have been discussed in terms of percentage deviations.