The Wild Burro Audio Labs Betsy 8″ driver is a favorite among open-baffle enthusiasts for its high sensitivity, smooth midrange, and budget-friendly musicality. However, like many wide-range drivers featuring a center dust cap or lightweight cone geometry, its stock configuration leaves room for acoustical refinement. Designing and 3D printing custom phase plugs for the Betsy is one of the most effective modifications to unlock its full potential.
Why Replace the Original Design?
The standard factory driver typically relies on a dust cap covering the voice coil gap. While functional for keeping debris out, a dust cap creates a small trapped air cavity above the pole piece. At higher volumes and specific frequencies, this trapped air acts like a miniature spring, causing “oil-can” resonances and internal reflections that introduce unwanted midrange coloration.
Additionally, wide-range 8-inch cones naturally begin to “beam” high frequencies as the wavelength of sound becomes smaller than the diameter of the driver.This results in a narrow “laser-like” sweet spot and uneven high-frequency dispersion off-axis.
The Phase Plug Advantage
Removing the dust cap and installing a precision-designed 3D phase plug transforms the driver’s acoustic behavior on two major fronts:
- Elimination of Cavity Resonance: A solid phase plug fills the dead space inside the voice coil, eliminating the air pocket responsible for midrange smearing. Vocal clarity and instrument separation become noticeably cleaner.
- Improved High-Frequency Dispersion: Actively guiding sound waves away from the center of the cone effectively halves the working diameter of the driver. This pushes standing waves up by roughly an octave, reduces beaming, and broadens the sweet spot across the listening room.
Get the 3MF file here and print your own Phase Plug!