Reflecting walls are equivalent to mirror-image virtual sound sources

Evidence

There is an alternative and very simple way of understanding the amplification effects of reflecting surfaces near a sound source: the method of images. We can illustrate this neat trick by returning to a single source near a straight wall. If you shine a flashlight into a mirror, the light bounces off the mirror back into the room. The light in the room is the same as if that image of you holding the flashlight in the mirror is real, pointing the flashlight into the room, with no wall present. The wall can be replaced by an identical, mirror-image “virtual” source symmetrically across the wall. The sound field on the “physical” side of the wall using both the real source and the image source, with the wall removed, is the same as only the real source with the mirror present. It is easy to compare the two approaches in Ripple, which confirms the equivalence. Ray tracing (figure 7.4) also shows that the reflected rays emerge as if from a virtual source symmetrically on the other side of the wall. — Eric J. Heller, Why You Hear What You Hear- An…, 515

Categorization

• DEFINE: Introduces the method of images for computing reflected sound fields.
• XREF: The same image-source method appears in architectural acoustics software and in optics for mirror problems. — connects to: A reflecting wall doubles total sound power output from any source; Room reflections can be modelled as sources in mirrored rooms — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 301; Room boundaries alter loudspeaker output through reflected image sources (+5 more)
• corroborated: 2 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 515

Broader Connections

• Room reflections can be modelled as sources in mirrored rooms #corroborates (0.95) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 301
• Room boundaries alter loudspeaker output through reflected image sources #expands (0.90)
• A single sound source near a reflecting surface creates interference via an image source #exemplifies (0.85) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 366