In room acoustics, many objective parameters to quantify subjective impressions have been introduced. These quantities can be measured by using a wide variety of powerful tools and equipment. The results can be in#uenced by the measurement techniques and instruments used. Furthermore, the results also depend on the measurement positions and on the condition of the hall (full, empty, etc.). The aim of this work is to de"ne a tightly standardized measurement procedure for the collection of a complete objective description of an opera house's acoustics. In this paper some of the results obtained by the authors after measurements made in three di!erent halls are presented. Comparisons were made both between di!erent hardware and software tools (real-time analyzer, DAT, PC-board, source, microphones, post-processing software) and between di!erent measurement methods (interrupted stationary noise, true-impulse, pseudo-random white noise with impulse}response doconvolution, sine sweep) as well as between di!erent positions in the halls, with and without the presence of musicians and audience. The results have shown that the di!erences obtained when using di!erent measurement techniques and equipment are not of signi"cant importance. The only e!ective di!erences were found regarding the recording techniques, as the monaural measurements give appreciably di!erent results from the average of left and right channel of binaural measurements. Slightly di!erent results were also found between true impulsive sources (pistol shots, balloons) and omni-directional (dodecahedral) loudspeakers. Attention must be paid to the signal-to-noise ratio, as this can in#uence the correct calculation of some acoustical parameters. Some di!erences, not as great as expected, were found in the results with and without the musicians in the orchestra shell and with and without the audience in the hall. This is probably due to the high sound absorption that is typical in Italian opera houses even without an audience. However, important di!erences were found in the calculation of some acoustical parameters, particularly clarity C80, by changing positions in the hall.