HD800 "French Mod" aka "SuperDupont Resonator"

I'm glad to see you have settled on a very similar final result to what I have found, guided by all of previous work of course. There are a couple things that I have done differently though.
1. I decided to use a 7mm hole instead of a 6mm hole the differences that I found however were quite negligible.
2. I am using a sponge material inside with a 10mm hole cut in it just like your felt, I found this gives slightly better results than the felt.
3. Finally the most important difference is that I am using a 16mm foam disc on the back side of the driver (the circle that you can see underneath the grill) rather than inside as I've found it delivers better results.

Here are some measurement results.
The subtle difference between 6mm hole w/ felt and foam behind driver (red) and 7mm hole w/ sponge and foam behind driver (green)

The mod that @sorrodje posted in post #188 (blue), stock with no dust cover (purple), and my version of the mod (green)

Just as an interesting measurement I tried using @Tyll Hertsens version of the anax mod on top of my version of the mod and the results were definitely worse with the anax mod.
My mod (green), w/ anax mod (mustard)

Here are some distortion measurements of the stock HD800

and then my version of the mod

 

Here I was thinking I was the only one.

 

Sorry about that, should be working now.

 

hahaha

Im in..... ,,,,, !!!!

 

Absolutely! Tomorrow I will try mimic your mod in post #220 and #234 instead of the post #188 version (non-closed bottom) I compared with my version of the mod (closed bottom on back side of driver) in my previous post. More measurements and pics of my resonator/absorber things to come tomorrow.

 

So hard to unsee.

 

Alright so I ran some more tests and measurements and here are the results.
Here is what I get from stock vs. the most recent version of the SD mod with the cardboard

Hard to differentiate the colors here but SD mod has lower 6k and more bass.

Then removing the cardboard from the back that closes the back and inserting foam on the back side of the driver hole as pictured below.
Before

After

Here the blue line is with the 16mm foam disc behind the driver and the red is the SD mod.

Then moving from a 6mm to a 7mm hole in the front foam. 6mm in blue 7mm in purple.

Finally here is the sponge material that I was using previously however I have found that the new felt that I am using actually performs slightly better.

Sponge in green, felt in purple

While the FR is very close the CSD is better for the felt and was the best CSD I have gotten so far.
CSD for 7mm hole in foam with 10mm hole felt lining and 16mm foam disc on back side of driver.

CSD for 7mm hole in foam with 10mm hole sponge lining and 16mm foam disc on back side of driver.

Some interesting results I still definitely want to do more experimentation though.

 

Broken pictures round 2. EDIT: Fixed!

 

Damn I don't know why google keeps doing this, I even checked it right after I posted and it worked. It should be fixed now. I'll get this figured out eventually. Anyone else here have more experience posting from google photos?

 

Imgur works.

 

Believe me, I didn't want to see it either.

 

Alright I fixed it... again! It seems like the links that google is giving are expiring or becoming not publicly viewable after a bit in some cases.

Yeah I'm starting to realise that now. I was just using Google photos because most of the photos I want to post are already on there so I don't have to download and reupload. But that's probably what I'll do from now on.

 

Works now.

 

It worked this morning, no longer working again. It might be a # of views, or bandwidth limit that Google places in order to prevent people from using Photos as like an ad-hosting server or something similar.