Timbre or tonal matching is in essence error matching. In a perfect world a speaker would no more have to be timbre matched than an amplifier.
Someone gave me a red star for that response, so I'm going to expound on this important point.
Timbre is character imposed upon the sound by a speakers imperfections. Really good speakers have little character, a perfect speaker would have none. However the state of the art is light years away from that goal at present.
Timbre or character imposed by speakers has a number of sources. Misbehavior of driver cones is a big item. This is especially true of cone break up modes. Different materials break up in different ways. Character imposed by different material has to be dealt with by appropriate crossover points, slopes and notch filters. In many instances this is not done properly and hence character or timbre rear its ugly head. Crossover errors are another potent source of problems. Even when done correctly lobing errors between fronts and mains can be a big source of discontinuity in the front sound stage. Finally we have the problems that cabinet resonances imparting coloration or character the sound.
So yes, it is these errors that give rise to the benign word of timbre. But any way you slice it any sonic footprint of a speaker is an error or deviation. So yes I'm well aware of what timbre matching is, but prefer as usual to call a spade a spade, lest we forget that speakers are still far inferior to the rest of the equipment in our systems.