Treating room walls as mirrors locates where early reflections need absorbing.
Evidence
Figure 7.25 shows one method of working out where absorption should be placed in a room to control early reflections. By imagining the relevant walls to be mirrors, it is possible to create “image rooms” that show the direction of the early reflections. By defining a reflection-free space around the listening position and by drawing “rays” from the image speaker sources, one can see which portions of the wall need to be made absorbent, as shown in Figure 7.26. This is very straightforward for rectangular rooms but a little more complicated for rooms with angled walls. Nevertheless, this technique can still be used. It is applicable for both stereo and surround systems, the only real difference being the number of sources. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2299
Categorization
- DEFINE: Introduces the ‘image room’ concept — mirroring walls to trace early-reflection paths, a core room-acoustics tool.
- XREF: Connects to the chapter’s earlier treatment of reflection and the precedence/echo-threshold effects that make early reflections audible. — connects to: Room reflections can be modelled as sources in mirrored rooms — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 301; A resistive absorber behind the listener solves reflective-wall problems where diffusers fail; Reshaping a room’s walls only obscures resonances rather than removing them (+2 more)
- corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2299
Broader Connections
- Reflecting walls are equivalent to mirror-image virtual sound sources
#expands(0.90) — Eric J. Heller, Why You Hear What You Hear- An…, 515 - Room acoustics requires modeling direct sound then early reflections
#expands(0.75)