Hello everyone! Sorry about the long gap as I was traveling. Before I traveled, I had made some progress which I could not update. The speakers were brought home to the listening room. Gasket lining done around the battens for baffle and around the cut out from driver. Polyfill (2 layers - total 40mm) filled along with the foam on all sides. The drivers were fixed using screws. I have connected the speakers without finishing and given them a test drive. Surprisingly decent for the money, but as expected - shouty and not much bass. I agree with a previous post about treble - its smooth, rolled off and definitely not refined but listenable.
I removed the foam from the cabinet and and only left felt lining and polyfill. There was definite improvement in the upper & lower mid-bass. It was now reasonably full bodied although one would still define it as lean. I also think there is non-uniformity in the frequency response as I can hear an occasional bass note which goes relatively low. This could be due to less than ideal damping or mismatch in port design (Don't know if I mentioned, but the port length is as per design, but ID is 2.75" as opposed to suggested 4").
After returning from my trip, I have tried increasing the damping in the box more. I doubled the polyfill. The box is now relatively full but not packed or overstuffed. Not much difference - actually it has been slightly negative. So I think 2 layers of polyfill (double sheet) is as of now what looks optimum.
I have not observed any hollowness or boxiness, so I think the box is not vibrating or resonating. Well, the MDF is 18mm and fixed with battens! So, I am going to try removing polyfill altogether and see if the bass increases without introducing any boxiness. There is anyway a 2mm fevicol-pasted felt lining on all sides (except front).
To control the shouty-ness, I did try light polyfill stuffing between whizzer and main cone. It is a decent mod and must admit it works - but - ever so slightly. I would still not listen to it this way for long duration. I must mention that some songs sound quite decent and attention does not go towards midrange harshness. These may be the few which probably don't have much energy in the range where this speaker is shouty.
Also with vinyl the overall the sound appears less shouty than with CDs/FLAC files!! It sounds more like a mid/vocal centric speaker but definitely less shouty. But I guess that is true for most systems and is beyond the scope.
In summary, it has not been a great build in terms of sound quality that I have come to expect after years in this hobby, but, there are still basic things to try to improve it - BSC, Stuffing, Port tube. And then there are more drastic things - like equalization, adding bass modules or trying a different full range 8" driver (the cabinet construction is very good and I am sure the volume will suit other similar drivers).
The photo album is updated and can be found here -
https://goo.gl/photos/vg42UXjkUgDdnUDB7. I also have some videos (shot through iphone though so not amazing but give an idea!) which I have to figure out how to share with those interested - suggestions? Just for info - the beautiful floorstander seen in the pictures is also custom made (not by me) using a coaxial Focal JM Lab 2-way driver. It is very professional work. These are my main speakers these days and have phenomenal bass response for the 6" driver. Very clever designing and construction by FM Pranav Kumar (Acoustic Science). Anyway, lets focus on the Hi-Q!