Each added perpendicular boundary halves the solid angle and adds a reflected acoustical image

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 (#expands, via linked claim)

Categorization

• XREF: connects to: Horns and boundaries both concentrate sound into restricted solid angles; Reflecting walls are equivalent to mirror-image virtual sound sources — Eric J. Heller, Why You Hear What You Hear- An…, 515; Each added boundary surface boosts sound intensity by 3 dB up to three boundaries (+1 more)

Related

• A reflecting wall doubles total sound power output from any source (similarity 0.91)
• Reflecting walls are equivalent to mirror-image virtual sound sources (similarity 0.91)
• Room boundaries alter a sound source’s radiated power, not just its perceived sound (similarity 0.85)
• Treating room walls as mirrors locates where early reflections need absorbing. (similarity 0.85)
• Boundary reflections create acoustical images that halve the radiation solid angle (similarity 0.84)
• Each added boundary surface boosts sound intensity by 3 dB up to three boundaries (similarity 0.83)
• Room boundaries alter loudspeaker output through reflected image sources (similarity 0.82)
• Room reflections can be modelled as sources in mirrored rooms (similarity 0.82)
• Reflections from a nearby hard wall can double the sound amplitude toward the listener (similarity 0.82)
• A single sound source near a reflecting surface creates interference via an image source (similarity 0.81)
• Boundaries alter bass output by changing the loudspeaker’s acoustical radiation resistance (similarity 0.80)
• A single boundary reflecting sound off an omnidirectional source creates frequency-dependent interference lobes (similarity 0.80)
• For short wavelengths, walls only confine sound rather than amplify its power. (similarity 0.80)
• Nearby reflective surfaces can load a source and boost its output (similarity 0.80)
• A single sound source near a reflective boundary creates a virtual second source (similarity 0.79)

Broader Connections

• Reflecting walls are equivalent to mirror-image virtual sound sources #expands (0.85) — Eric J. Heller, Why You Hear What You Hear- An…, 515
• Each added boundary surface boosts sound intensity by 3 dB up to three boundaries #qualifies (0.80)