Brilliance is the opposite fo warmth and exists if the reverberation time for high frequencies is larger relative to that of low frequencies. For an average room, the reverberation time for the low frequencies is slightly greater than that for the high frequencies owing to the nature of the absorption from the walls, floor, and ceiling. In a more brilliant room, the difference is less pronounced; the reverberation time for high frequencies is more nearly equal to that of the low frequencies. If the reverberation time for high frequencies is much too long, a continual high-pitched ringing sound may result.

Keith Jarrett: The Köln Concert