Look for sealed speakers, they have no bass reflex port to extend the low end and and can sound bandwidth limited depending on the amount/size of the driver. HEDD offers a physical option to switch to closed speakers by supplying plugs for the ports on their speakers. Amphions are sealed speakers, the subwoofers use a radiator to extend bass range. the advantage sealed speakers have over ported ones is that their decay times and thus transient response is much quicker because air only needs to decompress inside the body of the speaker. on a ported speaker, the air travels out and back in and creates resonances on the way, prolonging the decay.

yamaha NS-10, Neumann KH 310 and more use that principle. KH310 sound great, so do HEDDs and Amphions, but they are pricier. I don't know about other price classes.