Reflecting boundaries create image sources that alter loudspeaker load impedance.

Evidence

When a speaker is placed near a reflecting boundary, an image source is formed due to that reflecting boundary, as shown in Figure 1.28 in Chapter 1. Thus when a speaker is placed near three reflecting boundaries, three image sources are formed, as shown in Figure 6.59. The effect of these image sources, which represent reflections from the boundary, is to modify the local acoustic impedance seen by the loudspeaker. Because a dynamic speaker is mass controlled in its normal working region, it forms a high impedance source, and therefore the radiated power is affected by the local impedance variations. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2133

Categorization

• DEFINE: Introduces and explains ‘image source’ and ‘local acoustic impedance’ as the mechanism behind boundary effects — core terminology for the reader’s psychoacoustics grasp.
• XREF: Explicitly chains back to Figure 1.28 in Chapter 1 on image sources — depends on that earlier material being retained.