I post this for discussion. Jude uses an expensive isolation chamber by Herzan which he used for this testing:
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There is a potential problem here that boosts low frequencies. Let me explain.
The enclosure he purchased is made to keep noise from entering the chamber. That is not my concern here (I exclude noise from THD measurements using signal process so don't need the enclosure for that). The concern is what happens when sound comes out of an open back headphone. In a normal listening room, the walls are pretty far from the headphone so reflections become quite low in amplitude by the time to come back to the headphone. I experimented by putting a box around my headphone gear and it massively corrupted the frequency response (and distortion since it is relative to level of the signal). Any box put around a headphone measurement system needs to be fully anechoic, otherwise the reflections will change the response of open-back headphones such as Abyss Diana V2.
Here is the Herzan chamber Jude uses:
Notice how small it is so reflections won't have much distance to attenuate.
Then there is the issue of those foam absorbers. Those are basically useless below 1 kHz or so. Here is a quick graph showing that:
Look at that orange curve. It doesn't get to full absorption (alpha of 1.0) until you get past the right side of the graph at 4000 Hz! At 20 Hz absorption is just 10%. Wavelengths get so large in bass frequencies that you need feet of it, not an inch or two. This is why anechoic chambers are so expensive to build.
In addition, you also get "room modes" depending on where you put measurement fixture, causing response variations.
Now, I have not tried to build a chamber like his and see the impact. I just know that putting a box around the fixture causes massive error. Jude needs to experiment with measurements inside and outside of that chamber and see what effect it has.
Noise isolation is not needed for frequency response anyway when you use high enough level as I do (and he almost does). Neither is distortion impacted at the levels we are measuring and with proper signal processing to exclude noise.
I know Rting and Tyll both use similar enclosures although the latter two are home made. I think they automatically assumed there is goodness here, not realizing acoustics of sound and impact on open-back headphones.
the energy reflected back from open ear headphone is incredibly low. probably 5 to 10 times lower then what the mic is capting. then the amount of bass any open back makes is related to the pressure inside the cup. any open heapdhone when listened just 10 cm will have no bass at all.
then you need to take into account the distance the sound has to travel.
how can you seriously suggest that Jude box will boost bass.