Mayflower Mod on Fostex t20rp?

I found a discounted pair of what I thought were B-stock Fostex t50rp online. I intended on doing the mayflower mod on them as a project to fill a weekend that would hopefully also result in a nice set of headphones. When I got the email notification that my order had shipped, it turned out that I am probably an idiot and I apparently ordered the t20rp.

It looks like the only difference between the t50 and t20 is whether it has foam or a thinner mesh plugging the opening in the cup. everyone says the t20 has more bas, which runs counter to what I thought I understood, which was that open headphones usually have less bas because the open cup can’t be pressurized as much… whatever, If I’m going to do the mayflower mod I’ll be coating the inside of the cups with felt and it really won’t matter anyway, right?

Or… the reason why the T20 has more bas is because there is something different about driver, not the fact that it’s more open, and when I close them in with felt, the fact that the opening is closed will mean that the cup will be pressurized more and in combination with drivers that produce more bas, I’ll be turning these things into bas cannons, which isn’t what I’m looking for.

I think I’ve got my mind set on at least giving the t20 a try, the question is whether when I do the mod, I should cut-out a box in the felt in order to leave them open and prevent the bas from being over-bearing, or just do the mod normally because the result will be the same whether or not they started as a t50 or t20?

There are some complicated mechanisms and interactions at work when it comes to sound and enclosed spaces.
But yeah, in general, closed cup with some interaction of the driver leads to more intense response.

I don’t doubt that it’s more complicated that my oversimplified understanding. The t20 has more bass according to Fostex, confirmed by Zeos and it’s pretty apparent in the sound demo as well. Is it possible that the T20 could have more bass only because having thinner material covering the opening? If not, there must be some other difference other than the openness. If so, it might not be a good Idea to do a mod specifically designed for the t50. I might be better off just experimenting with pads and then making tweaks with the clay and felt inside the cups to see where it gets me.

generally more material = less treble more bass but can also depend on the material