The only important variable was foliage calcium, and once you know that, tree type itself (broadleaf or conifer, evergreen or deciduous) wasn't important. Thus although conifers generally lowered soil pH, and broadleaves raised it, the two groups overlapped. The conifer with the most calcium-rich leaves (silver fir, Abies alba) had about the same calcium as both pedunculate and red oak, and had a similar effect on soil pH. Hornbeam had even less calcium in its leaves, and produced the lowest soil pH of all the broadleaves. So the answer to the question "do conifers make the soil below them more acid?" is generally yes, but there's a lot of variation between species, and not all conifers (or broadleaves) behave the same.