Room Acoustic and Side Reflections


Room acoustic in general and reverberation in particular are based solely on reflections in the room, reflections on walls, floor and ceiling, reflections on each and every piece within the room.
Because of human's ability to sort out different reflections and to organize the received audible signal in a very sophisticated way to localize original sound sources and their reflections in the room so-called "good acoustics" are possible. "Good acoustic" is always a mixture of direct and reflected sounds and the reverberation field.

See: Precedence-Effect

Reflections - Mirror Images

mirror image caused by a regular reflection

Preferred Side Reflection Angles

Which reflections are received as "good" and which are received as "bad"? Valued side reflections within the proper delay range of 20 to 80 msec:


reflection angles received by most people as good sounding

"translated" into hearing angles

"translated" into concert hall acoustic

Early Reflections and Reverberation

early side reflections
- Apparent Source Width (ASW) -
early ceiling reflections
reverberation field
- Envelope (LEV) -

Surround Sound and Preferred Side Reflection Angles

Surround sound systems in compliance with the ITU standard ITU-R BS-775-2 are not able to represent the necessary room reflections that make a classical concert in a good concert hall enjoyable ! Because of the way the human hearing system is built, a side phantom image (as the front phantom image of two stereo speakers) cannot be created and a surround sound system by definition creates "only" ambience sound and side and rear effects. A surround sound system for classical music would need to have side speakers at 60 degrees ...
With the more variable setup of a 7.1 installation in compliance with ITU-R BS-775-2 and a side speaker placement as much to the front as possible a compromise could be reached but no recordings mixed this way are available ..


ITU-R BS-775-2 (5 ch.) and "good" side reflections

ITU-R BS-775-2 (7 ch.) and "good" side reflections

surround sound systems and classical music preferences don't fit !

typical reflections within the first 15 to 80 msec in a room with flat straight walls.
These few first reflections represent most of the received room impression ("good" or "bad" acoustic).

Typical Reflection Characteristics

straight reflection diffuse reflection concave reflection convex reflection

Audible First Wave Front

first wave front from direct sound,
straight source direction
'first' wave front from shortest reflection
changed source direction
'first' wave front from second reflection
changed source direction