FIG. 4.

Description of sound pressure variations over the TM surface and in the TR plane, relative to the projection of the EC axis onto the TM or TR plane [see (A) and insets in other panels]. Note that the view is rotated from Fig. 2 so that the EC approaches the TM from the top [as in Fig. 1(E)]. The manubrium is outlined, and the umbo is at the intersection of the crossed centerlines. |P_TM| and |P_TR| gradient direction is defined as 0° (arrow) when sound pressure increases from the postero-superior TM (lateral EC) to the antero-inferior TM (vertex). Nodal line orientation is defined as 0° when the nodal line is perpendicular to the EC axis projection. Gradient directions and nodal line orientations increase counterclockwise as shown by arrows. (B)–(F) (Top) Directions of |P_TM| (black open circles) and |P_TR| gradients (gray open triangles). Natural ECs: (B) TB13, (C) TB12; artificial ECs: (D) TB7, (E) TB13, (F) TB14. Also shown in the top panels are the orientations of P_TM nodal lines (filled circles) and P_TR nodal lines (filled triangles), where present. In most cases, nodal lines are visible only at the highest frequencies. Symbols denoting P_TR gradient directions and nodal line orientations have been offset −0.3 kHz and 5° for clarity. (Bottom) The location of the intercept of the P_TM (filled circles) and P_TR nodal lines (filled triangles) on the projected EC axis. Negative locations are above the umbo toward the lateral EC, positive locations are below the umbo toward the EC vertex [see panel (A) bottom].