Ultrasonic attenuation spectroscopy of a noncritical ethanol-dodecane mixture revealed a low frequency relaxation term. Considering this term in the spectra for the mixture of critical composition the experimental scaling function agrees well with the predictions of the dynamic scaling theory. Dynamic light scattering and shear viscosity measurements yield the amplitudes xi(0) = (0.37 +/- 0.02) nm and Gamma(0) = (6.4 +/- 0.3) x 10(9) s(-1) for the fluctuation correlation length and relaxation rate of concentration fluctuations, respectively. The adiabatic coupling constant results as small as vertical bar g vertical bar = 0.13 +/- 0.03 from the ultrasonic spectra and as g = 0.094 +/- 0.01 from the pressure dependence of the critical temperature and the thermal expansion coefficient. (c) 2007 Elsevier B.V. All rights reserved.