Normally the larger diameter of the bottom E (6th) will be louder and much depends on the diameter of the spring steel inner-core and alloy the outer wrapping is comprised of. Usually the larger the diameter of the inner-core the louder the particular string would be. The mass and alloy of the string will also determine the output of each string over a particular pole. That’s why you don’t see the lower strings such as the E-6th, A-5th or D-4th using just a solid core or plain spring steel. The mass of .042″, E-6th string would overwhelm the output of the .009″, E-1st string. A less magnetic material is wrapped around the lower strings for mass and tension. The specifications on the strings that I use are:

String String Diameter Core Diameter Outer Wrapping Diameter
E-6th .0425″ .0175″ .0120″
A-5th .0315″ .0145″ .0075″
D-4th .0240″ .0130″ .0055″
G-3rd .016″ Plain
B-2nd .011″ Plain
E-1st .009″ Plain