Acoustical attenuation spectra of the methanol-cyclohexane mixture of critical composition have been measured at different temperatures near the critical temperature. The noncritical background contribution of the spectra has been determined and subtracted from the total attenuation to yield the critical contribution. The latter enabled an accurate experimental determination of the scaling function. Regression analysis of the experimental scaling function data in terms of theoretical models yielded the relaxation rate of order parameter fluctuations as a function of temperature. Close agreement with relaxation rate data from other experimental methods has been found. The amplitude of the acoustical attenuation at the critical temperature has been discussed in terms of the adiabatic coupling constant. Its amount is likewise as small (\g\=0.14) as that of the alcohol-alkane system ethanol-dodecane (\g\=0.1). (C) 2003 American Institute of Physics.