When ceiling absorption is high while the walls remain reflective, a strong one- or two-dimensional horizontal sound field may develop. This can increase the risk of flutter echoes and produce a double-slope, or bent, decay curve with a comparatively long late reverberation time. The phenomenon may occur even in geometrically simple rooms because it is caused by the uneven distribution of absorption rather than by the room shape alone. The resulting decay can therefore be associated with two reverberation times: a shorter value during the early part of the decay and a longer value during the late part.

Adding more unevenly distributed absorption will typically affect the early part of the decay more strongly than the late part. Nevertheless, it will still reduce the overall sound energy in the room. The decay curve should therefore be assessed together with the sound pressure level (SPL). If the late part of the decay, where the longer reverberation time occurs, is relatively low in level, the practical or perceptual effect of the longer reverberation time may not be as severe.

Click here to read two relevant Application Notes about:

• Detecting flutter echoes in ODEON.
• Modelling simple rooms in ODEON.