As so many are saying here, just about any planar loudspeaker; Electrostatic, Magnetic-Planar, or Ribbon. In the past, there have been only a few available at any given time; now there are many, at all kinds of price points. Truth-of-timbre is one of the planar's greatest strengths, whether of strings, vocals, piano, or drums. I heard my first (Magneplanar Tympani-I) in 1972, and was instantly converted.
Dynamic speaker designers work very hard to make their products do what planars do effortlessly. But no matter what they do, a point source loudspeaker will always sound like a point source---a miniaturized version of a Grand Piano, for instance. A crossover somewhere in a critical frequency band will always be necessary with dynamic drivers. Enclosures of some sort will always accompany those drivers (except in the case of Open Baffle speakers, which have their own problems and limitations). Bah!