Just listened to some Fostex T50RPs today... WOW! - Page 306

I think he's referring to "Bass Lens".  Fostex used the idea in their original T50 or at least in their OEM version for NAD, in which they have a ring/donut of felt on the ear side of the driver covering only the outside portion with a hole in the middle.  Here's a nice picture that's been posted a few times in the ortho thread.  I find that it can also work to remove peaks in certain areas of the upper midrange and treble without reducing perceived detail (I find covering the whole front of the driver can cause a reduction of perceived fine detail)

This is one of the most interesting posts I've read - thank you!

The topic of variable layering of least dense materials closest to the driver to most dense materials at the internal cup surface for reducing reflections has been discussed on this forum, but not in as much detail as you described in your post.  Dynamat and other materials have been tried on the internal cup surface and covered with less dense materials including open cell acoustic foam, cotton, fiberglass, etc., with consequent reduction of cup volume that may affect the sound. Several people, myself included, have tried Dynamat in the cups with a covering of Paxmate or similar acoustic foam. I did not hear any difference compared to Paxmate, alone. I don't remember if anyone else posted their impressions with this configuration. Armaegis pointed out that Dynamat may add mass loading to the cup if placed on the internal cup surface but would not result in reducing reflections because its constrained layer is not against the cup surface and is essentially mounted backwards from its intended design. (Armaegis: correct me if I am mistaken about what you said.) This got me to thinking about how to better (?) make use of Dynamat.  On BMF 5 and 6 mod configurations, I removed the dust cover and its adhesive residue from the ear side of the baffle surrounding the driver. Next, I placed Dynamat on the exposed plastic surface surrounding the drivers. To diminish reflections from the metallic-looking Dynamat constrained layer, I covered it with self-adhesive felt. 

After reading your post, I am now going to place AcoustiPack Lite in the cup bottoms (not the sides) to take advantage of its constrained layer (most dense layer the greatest distance from the back of the drivers). Next, on top of the AcoustiPack I am going to add 1 layer of Paxmate (not the sides) to take advantage of its (I presume) less dense and greater quantity of open cell foam in closer proximity to the back of the drivers. Everything else in my "Less Is More" and "Transpore 1.5" mods will remain the same, as described in post 4513 a few pages back, including 1/2 of one medium cotton ball loosely teased and placed between the Paxmate and the back of the driver - the least dense material closest to the back of the driver.

BTW, would you describe "bass rings?"

BMF, I'm really surprised that you'd hear more bass with more of these vents open.  Kind of goes against all the conventional wisdom about it.  But we could be mistaken, or the T50rp could somehow be different, so keep exploring!  Maybe the key is a small hole, or where it is placed so close to the driver. 

quick question. I'm sure I could ask this in some other thread but oh well. Is plasticine the only type of clay I should use for the inside of the baffle on the T50RP? Or will any similar modeling clay work?

I used Sculpey with good results.  Just so long as it doesn't air dry it should be fine.

Anyway, after using these for awhile, I'm really missing the comfort of my 595s...I just can't wear these for longer than an hour before having to give my ears a break.

I used Sculpey with good results.  Just so long as it doesn't air dry it should be fine.

Anyway, after using these for awhile, I'm really missing the comfort of my 595s...I just can't wear these for longer than an hour before having to give my ears a break.

Is that with the stock pads? I'm planning on getting SRH840 pads at some point.

Make sure you do the simple headband mod. For me it made wearing these headphone more comfortable.

Yup, I did that, though it's a bit sloppy right now.  Definitely makes it more comfortable but it doesn't fix the earpads.  Pretty damn uncomfortable...they're too shallow and my ear rubs up against the side/back.  Stuffing tissues in the back of the earpads does help significantly, but the earpads themselves are just too hard to mold to my head properly...hopefully the 840 pads are at least a little softer?

The 840 pads will be softer but what is even better is if you sandwich the T50RP pads with 840 pads.

I used Sculpey with good results.  Just so long as it doesn't air dry it should be fine.

Anyway, after using these for awhile, I'm really missing the comfort of my 595s...I just can't wear these for longer than an hour before having to give my ears a break.

Arleus,

Your drawing is actually pretty descriptive.

About the sponges, while I think one posted in http://www.head-fi.org/t/452404/just-listened-to-some-fostex-t50rps-today-wow/4410#post_7864126 may not be very good, the one in http://www.head-fi.org/t/452404/just-listened-to-some-fostex-t50rps-today-wow/4410#post_7864064 is probably optimal as the first layer of cup filling.

Btw, what is the difference you've got when you removed paxmate from around the driver on earside? What was the sound like before that removal?

Looks great! 

If this config suits you, that's all that matters.  Could you describe the SQ, bass/treble extension, midrange clarity, etc. compared to stock?

BTW, very cool graphics. What software did you use to make your "drawing?"

"You" (not you specifically) also have to know how to read an FR plot even with the transfer function calibration he uses.  Ideal is not a flat line, the way LFF's measured was close to ideal similar to the LCD-2 with a flat line from bass to midrange, a dip in the upper mids, then a small peak, then a few more minor ups and downs.  The peak does look a bit bigger than ideal though and the line is wobbly in the midrange to bass (but maybe close enough as to not be audible...).  As for the channel imbalance, Purrin picked that up in his test too, so I don't think it's Tyll's measuring equipment.  I wonder if it might be the big black cable connector box inside the left earcup.  It bugs me that they aren't symmetrical. 

This.  Every time I pulled mine apart, that connector box kept looking at me to tell me that even if I got another T50RP and transplanted the second connector box equipped cup...it might be volumetrically matched...but not visually.