The Great Hall of the Moscow P.I. Tchaikovsky Conservatory is one of the best concert halls in Russia. Its acoustics is appreciated very much by both musicians and audience. In 2011 the Great Hall was renovated, after renovation its acoustic conditions remained at very high level that was confirmed by means of objective impulse response measurements and subjective estimations. In order to control how acoustic conditions are changing with time the observation of main acoustic parameters is carrying out with half year gaps. In this work we present the results of four measurements fulfilled in June 2011 (just after the renovation), December 2011, June 2012 and December 2012. The reverberation time decreases at low frequencies, whereas it is stable at middle frequencies. Periodic variations of the reverberation time take place at high frequencies. These variations are probably connected with seasonal changes of temperature and humidity conditions in the hall. Changes of other acoustic parameters correlate to the reverberation time.

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