Literature on Tuning Frequencies -- Port Science, Sony 1R vs 1A example

Is there any information someone can recommend to figuring out port tuning frequencies on a level that could somehow/somewhat be applied to headphones? Back in my 'ol days I used basic acoustic modeling software for loudspeakers (namely subwoofers) in car audio but I'd like some research material on the acoustics going on with headphones, such a thing exist?

 

Maybe a specific example to what I'm interested in might be worthwhile. Below is the port on the MDR-1R:



If you can't see it from the pic, there is a rectangular slot with a acoustic resistor on the right coupled with the obvious undamped hole. On the MDR-1A the hole is larger and the undamped hole actually has a longer length (a boss is made on the port to lengthen it, whereas the slot port is narrowed (but maybe lengthened slightly, I'm not sure). I assume the slot area decreases and the hole size increases. Does this lower the tuning frequency and or increase port gain? As the measurements here on the site would indicate, the 1A has a much more significant sub-bass kick than the 1R. The 1R has a rolled off sub-bass, likely being below the tuning frequency and suffering the steep rolloff (3rd order, right? 18db/octave?). The 1R has a midbass kick, so is the port gain just as significant in either case but just at a higher frequency? If anyone can contribute any thoughts it would be great!

 

In the MDR-1R's case, blocking the vents causes all the lower bass to be killed. It's there to help with subbass equalization, if simply modding for an improved signature it's probably better to leave them alone. A simple placement of dynamat on non vented parts of the baffle and drivers do wonders to help bass impact and bring down midbass, helps kill bass bleed into mids too. Stuff with some fiber to finish off and the already improved subbass performance of the 1A should get you where you want

 

I'm curious about this type of thing too. I would love to have some good pointers when it comes to port tuning on headphones. It seems it's mostly about venting rather than actual ports. A port is tuned to a frequency, and acts as a helmholz resonator. A bass vent lets the speaker move move with less resistance. But in many cans, altering the port sizes and numbers will either affect all bas from a certain frequency and down, or only a certain frequency band. For some cans all you can do with vents/ports is increase or decrease the mid bass hump. With somebot almost acts like a low shelf filter. I don't get what makes it do one or the other!