References for acoustics in music rehearsal rooms:

The ideal reverberation time depends on the size of the room and lies between 0.4 and 1.0 seconds.
For music rehearsals and music lessons, the frequency response of the reverberation time should be linear, as this increases the perception of sound (in contrast to the musical performance, for which the reverberation time at low frequencies should increase slightly, this increases the warmth of the sound).