Warmth is obtained when the reverberation time for low-frequency sounds is somewhat greater than the reverberation time for high frequencies. The `ideal' reverberation time, as function of frequency, required to obtain a feeling of warmth is roughly given as follows: Above 500 Hz the reverberation time should be roughly constant, but below that frequency it should increase to about 1.5 times the reverberation time for high frequencies. This is accomplished by the proper choice of material for the walls and ceiling. If the reverberation time is too long at low fequencies, the sound can become muddy and will lack clarity.