This question gets increasingly complicated.

I often end up with wines that have pH's that are either too high or
too low, and the best solution is to blend the two. My question is how
to predict the resultant pH.

Obviously, pH is a log function, so blending equal parts of wines with
pH's of 3 and 4 DOESN'T produce a wine with a pH of 3.5. A wine with a
pH of 3 has 10 times the concentration of H+ ions than a pH of 4. Does
anyone know of an equation to predict a resultant pH of a blended wine
the following 4 variables:

X = volume of wine with pH of A
Y = volume of wine with pH of B

My goal is to work backwards and aim for a specific pH, knowing the
pH's of the original components and then calculating the necessary
volumes of the two components. While bench trials are another
solution, there should be some science to predict the results.

Thanks for your help,

Lee