Speaker and instrument directivity at high frequencies alters perceived timbre

Evidence

Most hi-fi loudspeakers and musical instruments are omnidirectional at low frequencies but are not necessarily so at higher ones. As the level of the reverberant field is a function of both the average absorption and the directivity of the source, the variation in directivity of real musical sources will also have an effect on the reverberant sound field and hence the perception of the timbre of the sound. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1796