Edge diffraction and the baffle step
Two effects of cabinet shape, as distinct from cabinet stiffness, on what a loudspeaker radiates. Both are sourced here from one manufacturer interview (rockport-enclosure-design-interview), which credits Harry Olson's 1950s cabinet-shape experiments for the underlying result.
- Baffle step. At high frequencies the driver radiates into the half-space in front of the baffle (2π); as wavelength grows past the baffle's dimensions the radiation becomes omnidirectional (4π) and the on-axis level drops. The step cannot be removed, only smoothed — a broad chamfer or continuously varying baffle width spreads the transition over a wider band.
- Edge diffraction. The wave travelling across the baffle meets the sharp edge and, in Payor's phrase, "snaps off" it, becoming a second source displaced in space and time from the driver. The two combine into comb-filter ripples and phase anomalies. Any discontinuity — a step, a gap, a grille frame — does the same. The mitigation is the same broad facet or radius; a small roundover does little.
Why the spoke cares: these are the effects that a perfect alignment and a perfect box leave untouched, and the interview's claim is that they decide whether a speaker "disappears" as a source. Unmeasured here — the source gives no ripple magnitudes, no frequencies, no comparison of edge treatments. A T2 measurement (Olson's original curves, or a modern baffle-simulation study) is the closing source.
Related
loudspeaker-enclosure · rockport-enclosure-design-interview · crossover · synthesis