An Important Aspect of Underhung Voice-Coils: A Technical Tribute to Ray Newman

In the 1970s, Ray Newman while at Electro-Voice, single handedly and very successfully promoted the use of the then new concept of the Thiele/Small parameters and related design techniques for categorizing loudspeakers and systems to the loudspeaker industry. This paper posthumously recounts the contents of three significant Electro-Voice memos written in 1992 by Ray Newman concerning a comparison of overhung versus underhung loudspeaker motor assemblies. The information in the memos is still very relevant today. He proposed a comparison between the two assembly types assuming motors that had the: 1. same Xmax, 2. same efficiency, 3. similar thermal behavior, and 4. same voice coil. He calculated the required magnetic gap energy and discovered to his surprise that the magnet requirements actually went down dramatically when switching from an overhung to an underhung structure and depended only on the ratio between Xmax and the voice-coil length. This is in contrast with "common sense" that dictates that longer gaps mean larger magnets. He showed that for high-excursion motors, a switch could be made from a ferrite overhung structure to an equivalent high-energy neodymium underhung structure with little cost penalty. This paper recounts this early work and then presents motor predictions using present-day magnetic FEM simulators illustrating his concepts. Ray's original memos and notes will also be included as an appendix to the paper.