The Isophasic Waveguide
By Steven Desrosiers
The new KF810P loudspeaker with isophasic waveguide technology is our latest technical breakthrough which transforms the acoustic high frequency source to a true isophasic output.
Designed in the EAW engineering laboratory in Whitinsville, Massachusetts, our patent pending, isophasic waveguide with a Tri-ovular Bi-lens Conoid™ Phaseplug is a new development in the field of acoustic research.
The innovative waveguide equalizes the path length from the transducer to the horn aperture to achieve isophasic output that intrinsically controls the vertical and horizontal pattern. This is achieved by controlling the lengths of the acoustic path from any point at the acoustic source to the corresponding relative point at the exit, while controlling the coverage angles with the exit.
The output is maximized by ensuring laminar propagation with controlled expansion through a single minimum curvature and minimum surface area acoustic path. This results in a gently curving wave propagation that forms the wave-front into the ideal line array coverage pattern. The absence of abrupt changes in the direction of the acoustic energy ensures no internal acoustic reflections.
To achieve the isophasic wavefront, we’ve designed the waveguide using evenly distributed open-area cross-sections along the single acoustic path. We define multiple tangential length-equalized control splines through relative corresponding points on each open-area cross-section. We minimize acoustic path curvature by equalizing all control splines to the shortest achievable spline determined by a required waveguide length. The inner boundaries of each open-area cross-section define the exterior of the conoid phaseplug; the outer boundaries define the waveguide shell. Designing in this manner ensures that the energy entering the horn aperture is time-aligned across the exit, “Isophasic”.
By testing varying vertical angles of the waveguide exit aperture, we’ve confirmed the vertical exit aperture angle combined with the acoustic high-frequency di-pole results in the vertical pattern that works best for the KF810P application. Further testing confirms the wavefront needs to exit perpendicular to the waveguide exit aperture in the horizontal plane. Waveguide designs with more pronounced horizontal curvature, results in a horizontally-splayed, non-perpendicular wavefront and less-than-ideal horizontal pattern control. EAW’s Isophasic Waveguide begins vertical pattern control within the waveguide, while providing an optimized wavefront for horizontal pattern control by the large adjacent horn.
Minimal Pathlength, Narrow Overall Width, Minimal Variation from Entry/Exit Axis
The smallest acoustic pathlength is critical to ensure minimal curvature in the waveguide design. In this application, the smallest pathlength begins at the waveguide entrance aperture and splines to its relative point at the top or bottom of the rectangular exit aperture. All other acoustic pathlengths need to be equalized to this minimal pathlength to achieve the isophasic wavefront as described above. By equalizing all the acoustic pathlengths to the ideal minimum length, the resulting curvature of the control splines remains narrow, resulting in a narrow overall design with negligible direction change for the acoustic wave as it propagates along the acoustic path. We tested with many waveguide variations with equalized pathlengths of greater length and curvature to confirm that reducing the curvature and width improved phase, output and directivity.
Minimal Surface Area Pathway
We have achieved the isophasic wave-front without having to simulate the phase-alignment with multiple paths or internal fins. We have tested waveguides with multiple equalized pathways and found reduced output and reduced pattern control. The added fins increase the surface area around each of the acoustic pathways and results in increased drag and decreased air movement along the waveguide surface, resulting in performance reduction.