Engineers build ‘rotary’ speaker to recreate 1930s organ effect without any moving parts

Electronic engineers at the University of Nottingham have found a new way to create sound effects. They manipulate how sound waves interact with each other, a technique that could open new possibilities for music performance and production. The approach falls somewhere between traditional electronic and mechanical sound effects, occupying territory researchers say has gone largely unexplored. The findings were published in the Journal of the Audio Engineering Society.

The team built a novel solid-state “rotary” speaker inspired by the classic Leslie speaker, an electromechanical effect first developed for electric organs in the 1930s. Instead of relying on moving parts, the new device uses a circular array of speakers, translating the signal electronically across that array rather than mechanically to emulate motion.

Modulating waves, not signals

The original Leslie speaker uses motors and belts to physically move horns and baffles, creating sound modulation through actual motion. That design left a lasting mark on popular music. It inspired a wide range of emulations and variations now common in electronic, digital, and software plug-in formats, including phasers and chorus effects.

Despite that popularity, the character of the original acoustic-mechanical effect, produced by sound sources physically moving through space, is widely considered superior to its electronic and digital imitations. Nottingham’s new device tries to close that gap differently.

Rather than modulating an electronic signal on a single fixed speaker, it modulates the phase of physical sound waves as they approach and surround the listener directly.

Researchers say that distinction gives the resulting effect a more organic character and greater perceived depth than conventional emulations can achieve. The solid-state rotary speaker represents the field’s first real attempt to capture the original Leslie’s character without inheriting the impracticality of its mechanical components.

Innovation since the 1990s

Fernando Perez-Cota, an assistant professor in Nottingham’s Department of Electrical and Electronic Engineering, described the field’s usual limits. Sound modulation for music has traditionally existed as one of two options: acoustic-mechanical, like the original Leslie, or electronic-digital, with no meaningful middle ground between them. He described this work as the field’s first genuine attempt to blur that boundary.

Researchers frame the development as the first significant innovation in sound effects since digital modeling techniques emerged in the 1990s. That gap spans roughly three decades of largely incremental refinement, rather than genuinely new approaches to the underlying problem.

Nicholas Wolstenholme, a master’s engineering student involved in the project, said the concept extends well beyond simply replicating the Leslie speaker’s specific character. He described it as representing an entirely new paradigm in sound effects and modulation more broadly. That paradigm could deliver high-quality sound effects at a cost and scale accessible to virtually anyone making music, rather than remaining limited to specialized or high-end equipment.