Hi krikan,
Thanks to Adrian for the definition of "timbral" differences.
If you want to do a simple and quick demonstration of the coloration (or timbral signature) effects on sound, have someone talk to you in a normal voice and then as they are talking, tell them to cup their hands around their mouth as though they were going to yell to make their voice carry farther.
You will hear an immediate change in the tonal quality (timbral signature) of his or her voice. That is what happens when a loudspeaker "horn-loads" a driver. It's an unnatural coloration or timbral change.
You can even do this demo yourself if you have a bathroom with a bunch of reflective tiles. Just face the mirror and keep talking then cup your hands around your mouth and you'll hear the change in your own voice. It's a quick and fairly dramatic demo of horn coloration in speakers. It adds a slightly nasal quality to the voice that's not accurate.
Our ears are acutely sensitive to sounds in the midrange, so that is why we notice any slight tonal (timbral) colorations on dialogue in the front three speakers (and the surrounds, if the colorations are blatant).
Regards,
Alan
