Terrible place to develop a spike, though perhaps not so bad based on the minimal transient valleys fore and aft respectively speaking.  That's bass response is just ridiculous custom or otherwise.

It seems like they were really tuned around the assumption that they would be a very shallow fitting iem (which the shell design forces).

In terms of real life bass performance, people have been saying, here and there, that the shure 846 has more bass, which I think is clearly a function of people having a poor fit. Because dang.


I'm thinking of picking up a pair again and playing with further limiting the vents, although not totally occluding them, plus adding a filter at the nozzle to thicken the treble and reduce the bass just a little. Think it'll work?

846 does have more upper to mid bass.  Of course it has different filters so....

Aren't the vents just for treble EQ? In this case, you could argue that the Helmholtz resonators are actually "anti-resonators", and introduce diffraction-induced nulls in the back wave of the transducer.

BTW, the placement of the "remolded" IE800 is such that the equivalent insertion depth (port head is still distal to the first bend) is still relatively shallow, so it has "correct" placement that replicates Sennheiser/Axel Grell's intended design characteristics. At the same time, the pathway from port to ear drum is substantially different because the canal portion from first to second bend is now essentially a curved regular cylinder. While this makes "tuning" more predictable, it also changes the dynamic of the IE800 interacting with the residual canal volume of the ear. For CIEMs, it's "supposed" that because everything is molded up to the second bend, then residual canal volume is ~0.5 cc, and usually takes on a regular cylindrical shape, so the "standing wave" argument for predicting ear canal resonances works, at least partly, and in this case, an industry standard IEC60318-4 ear simulator can be used in a controlled fashion. Sennheiser with the IE800 switched up the game. They use the entire 1.5cc volume from the first bend to the ear drum, and while ear simulators still work in limited fashion, their reproducible data is limited. That's why Tyll had such a hard time trying to measure the IE800 (in addition to it not fitting correctly in the fake ear). IME, ear simulators have problems with off-axis (pitch/yaw) measurements (because they introduce the most asymmetries in a compression wave, leading to resonances/nulls), but real ears and real people often wear their earphones off-axis and their ear canals are irregular in concavity. Ear simulator measurements should be at best a reference of a singular wear scenario.

The D2CA seems to work on treble only:



But I take it you mean the vents:



It's not really possible to know what the "thin treble" is due to. More likely, it's a property of the "XWB" driver and whatever material/construction it's made of. Just like loudspeakers, I find that mass-driven excursion and surface treatment of the diaphragm/("cone") strongly influences "timbre" and the driver's breakup nodes. With respect to bass, I always find that closing/limiting bass vents makes drivers sound "less good". The FR gets corrected, but the driver always sounds "off".

We'd have to look at Sennheiser's internal data to really know what effect these resonators and vents have on decay, and that's not really possible; there's no "WikiLeaks" for hi-fi.