HD800 "French Mod" aka "SuperDupont Resonator"

Some more probably wrong thinking but...

I was thinking about how my speakers hadn't received much attention recently and then the following hit me...

I have owned a lot of bookshelf speakers in my past and many of them were ported with removable foam bungs. Of course these ports are all helmholtz resonators tuned for a lift in a specific frequency. The foam bung makes this system into a helmholtz absorber and drastically attenuates this frequency when inserted. In any case I just can't remember any foam bung ever having a hole in the middle of it but the HD800S has. Right so my strange conjecture is that the small hole in the middle of the acoustic absorber is acting again as a helmholtz resonator for the very high frequencies (remember how the HD800S has a slight high frequency lift compared to HD800?). Forgive me if I haven't read all your posts and I am preaching to the converted! It would be interesting to find out if the HD800S acoustic absorber 'hole' is just a hole in acoustic foam or if indeed it has a more solid wall than the acoustic foam that surrounds it. Anyway I will do the maths to predict the high frequency lift but I need the HD800S hole diameter inside the acoustic absorber and is the absorber tapered at the end?

Cheers

 

My last post, I promise! Well I did the maths and I'm wrong. The hole in the absorber is not going to boost the treble but boost the low end. With all of my assumptions i.e. using the 6kHz peak to generate an approximate air volume and then using this calculated air volume and approx dimensions of the acoustic absorber hole of width 10mm (had to use pictures and guess) and approx depth 5.5mm (love to know if that is the real depth) I calculated the generated helmholtz frequency of 296Hz. Note there are so many squares and square roots involved that any error in my measurements will give a large shift. But even my approx measurements make me feel certain that the hole definitely boosts the low end. So the hole is critical and needs more examination The cool thing is that by understanding how this stuff works that we can all tune our HD800 exactly to how we want. Next week I will start playing around with foam and hole sizes as the rest of you guys are. Enough from me I promise!

 

Hav you tried the bluecell tips?

 

Maybe you can make a list so others won't try what you already tried..

I see most of them using a slowmemory foam...

This one may be different as it has "heat activated " type foam:

ALIMPIA Replacement Memory Foam Ear Tips Eartips For Most Earbuds In-ear Earphones Grey M Set of 2 Pairs https://www.amazon.com/dp/B0182GPIQY/ref=cm_sw_r_sms_awd_YaXPwbCCY5B91

 

Thanks Sorrodje, do you mean 14mm ? If so then yes that is the measurement I have used with my formulas. By the way I spent my holiday (Australia Day) doing Maths and your mod. I used dense foam and drilled out the centres to approx 7.6mm diameter. I redid my calculations and found that this diameter gave a helmholtz frequency of 72.28Hz. What I heard was more bass but too much so for me and it was a little muddy. Then I replaced with high density foam with no centre holes and the bass became normal but I found the highs a little too much reduced for my older ears. My next step is to use a less dense foam and then apply foam glue to the centre to achieve a smooth internal cylinder. My hope is that this will give a little less 6kHz attenuation than the high density foam but a clear rather than muddy bass lift down low.

Cheers

 

Alright so out of curiosity, with @whipped's idea and the fact that the tubing of the Shure tips can keep a great center piece, I'm gonna try open cell foam, but with a cut out tubing in the central point. http://i.imgur.com/Ccjb0n5.jpg < cutout open cell foam + the cut to size tubing of the Shure tips. Maybe that offers the sweetspot since the tubing in seems to measure better?

 

Another thing to consider is how we are measuring the headphone. Consider a speaker with a port. The speaker does not appear to have more bass until it is loaded with a hand a few cm away from its port or is close to the wall etc. If we are not measuring the headphone 'loaded' ie on a dummy model or with some kind of mass over the open ear cup then we possibly may not be getting the full picture.

 

Very interesting! Did you have the 3mm of tip pressed down into the hole, or is it flush with the top of the hole, with empty space underneath?

I think if we are only aiming for 3mm in length, the revised/new version of the shure tips, with tubes left in place, becomes an option because you would be cutting below the wax screen.

 

Late last night I tried a different type of foam. I took the bungs out of my speakers and in the name of science I cut them up just enough to make absorbers for the HD800. I could breathe through this foam and it did work well in attenuating the 6 kHz spike, but I didn't have time to generate frequencies and test it with my ears.
I just worked on the absorber to establish which materials worked best.
If I could establish that the 14mm inner cylinder diameter was the same on the HD800S (i.e. the outer diameter of the HD800S acoustic absorber it would really, really, really help me

 

Has anyone tried same tip in larger size, yet squeeze to fit in..
I am supposing a denser amount of foam may aleviate the 4k range from being touched...
Edit"
@sorrodje,
You mentioned older tip, which I assume may have been more compressed over time..

 

Since we are looking for the elusive Sennheiser material. ..
Could it be as easy as this?

 

Ok, just spent an hour with my wife and daughter where we listened to test tones 5 kHz, 5.5Khz , 6kHz and 6.5Khz to identify which was the loudest when using acoustic foam (cut from baffles of Q Acoustics Concept 20 loudspeakers) stuffed into the centre helmholtz resonator of HD800 to create an absorber. The thickness was around 6mm and there was no additional hole in the middle to boost the lower frequencies. What we consistently found was that the 5 kHz tone was the loudest to the human ear followed by 5.5Khz then 6 and 6.5Khz. The absorber is effectively working then and there was a clear difference between each tone with 100% repeatable success rate.
Interestingly when using the sticker mod there were dual peaks at 5.5Khz and 6.5Khz.
Back to the French mod, my thoughts are that there is a balance point between 6Khz reduction and low end boost. If you try to boost the bottom end with an additional helmholtz resonator as in the HD800S and boost it too much you will lose the ability to absorb the 6kHz really effectively. Also you can really destroy the 6kHz peak if you are willing to forego the volume required by the additional resonator. So there is a balance point which Mr Senn obviously has correct. Note all of these measurements were done by ear and that the 6-6.5Khz may actually still exist to the microphone but not to the ear when natural rolloff is accounted for.

 

I have just trimmed these absorbers to 4.5mm depth and retested using Audacity. Now my 6kHz band is very even with the 5 kHz to my ears and the headphones sound really good i.e. delicate treble. Remember this does not boost the bottom end just tames the high but there are some HD800 which hit 5dB and don't need the boost.

How to personally tune your HD800 to suit your ears (6kHz).
1) Download Audacity (I use Mac) and open new file
2) Go to 'generate' on top menu then select 'tone' on the drop down menu
3) Generate as many tones as you need of 1s intervals (I chose 5,5.5,6,6.5 Khz) every time you generate a tone press the fast forward button (arrow button) to allow next tone to be recorded.
4) start with the longest absorber as possible and progressively cut down to achieve your desired tonal balance.
5) You now have a headphone personally tuned to your ear.

 

What I have concluded personally is the same as @OJneg (read more here: http://www.superbestaudiofriends.or...-hd800-mod-impressions-and-permutations.1149/). For the most effective damping, elevating and generally preferably sound you need more than just a resonator.
Step 1: Resonator to tame the treble with slight bass extension.
Step 2: Damping the trapezoid + metal ring for slight reduction of the 6k peak and slight uplift of the 4k dip. Also with certain material on the trapezoid (in my experience Dynamat) there's more pronounced (not muddy) bass and slam.
Step 3: Absorber either just on the mesh or fully covering everything side the ring. Elevated upper mids, further reduction of the peak and more balanced tone.

Now if we can have the Resonator to tame treble as effectively as possible, preferably without any extra dips on the 4k side as @sorrodje is researching (thanks for all the efforts btw!), then we have something very, very exceptional going on close to Sennheiser and maybe even beyond it. Step 2 in general will be just for the people that want the last few %. Step 3 is essentially the existing rugliner, bath mat or SBAF mod.

So what I'm also thinking, how about a 3mm cut of the foam tips and instead of paper something like cork on top? Like 1-2mm. Wouldn't that do both what @whipped has researched and what @sorrodje has researched? Cork is exceptional in my analyses of about 10 different types of material for the trapezoid/ring (thanks @Besnia).

For now I'm awaiting @sorrodje's analysis.