ABSTRACT
A lot of discussion on loudspeaker behaviour is based on mathematically simple point sources, but real loudspeaker drive units have a physical size and must be mounted with some space between them. If they are mounted on a flat baffle as in Figure 10.1, their acoustic centres (the position from which the sound effectively radiates) have different horizontal distances from the baffle position. If we take our listening position as in-line with the tweeter axis, as is usually done, then there is a greater distance from the ear to the MID unit and an even greater one to the bass unit. To minimise the differences, the drive units are normally mounted as close together as physically possible. We therefore have two effects giving rise to different distances from drive unit to ear and hence differing delays in the arrival of sound:
1. The vertical spacing of the drive units 2. The different distances between the drive-unit acoustic centres and the front baffle
I am assuming here that the drive units are mounted in a vertical line. This is almost always the case as it gives the best horizontal directivity.
