I've just had a big Eureka moment with my HD250 Linear 1s last night, as I finally got them right. All the pads I'd used until then varied between great moments and blech, but not consistently excellent ... until the arrival of the HD430s, which I had originally intended to use for parts, headband, pads, rings. They are in such good nick I tried to really enjoy them as they were, but they were so reticent in the lower bass no matter what combo of cable and pads, that I went back to plan A. Took the headband and pads with their rings, perfect fit! Made sure the HD400 foam pads were centred correctly (to replace the rare inner original concave foams) and the new pleather pads from the HD430s just clipped right in there. Add Mogami cable and holy moly do these things now sound
right! The bass now goes as genuinely deeep as the HD540 Ref1s (not as stock) and has loads of detail with that, taut, weighty and extremely rhythmic, just like the Ref1s. Mids and top end are so even and lacking in edge or spit without being soft, articulate, that I am now really loving these cans, just when I was almost ready to give up on them. Just a touch of mid bass plum, yet there's no reduction in detail for that. Plenty of stage depth too, surprisingly so. Stunning for closed back cans.
I've learnt a lot from my Sennheiser and recording tech pal, especially finding that it is essential to get those concave foams (difficult) or do the next best thing, as I've had to do, order a set of HD400 foam pads from Sennheiser (as the foam density is genuine Senn and not cheap Chinese) and use them instead. They are almost a perfect height in both the edges (around 12mm) and centre, at around 1-2mm. The raised edges allow the bass to flow correctly around the pads from the bass tube behind the driver, this is what creates the linear bass response and now that I've heard the difference between having it right and not so, just do it! I'm shocked at the difference. Plus, the pleather pads from the HD430s are a perfect match, the leather 'orhpolsters' for the HD250 thicken the mid bass and don't allow the bass energy to flow correctly. The pics below will explain. And make sure you have the white felt rings, these are crucial! I hope they're useful for someone. I've heard that some folks take out the bass ports and fiddle around with the capsules, but really, now that I'm hearing them properly as they are, I'm certainly not going to bother with any more shagging around with them, they truly are remarkably Linear
If you're missing the correct foams, I have put the eBay address below to pick up a set of the HD400 pads. The pics of my own Linear 1s show clearly the thick edge of the HD400 pads peeking from below the edge of the pleather pads.
My own HD250 Linear 1s seem particularly cable sensitive. Best by far is the Mogami cable (available from Venus Audio on eBay)! Wide and deep s/stage (where present in the recording), a natural openness, beautifully even from the deepest bass to the very top end, gorgeous vocal naturalness.
Trailing somewhat behind, with it's narrowed s/stage and lessened bass quality, comes the HD6xx stock cable (it has the same effect on the HD6xx, BTW, just slightly less so). Lastly, by some distance comes the stock cable that came with the HD430s, which is the same as the stock HD540 cable and from what I've seen with the early HD250s - anaemic, upper mid edgy, narrowed s/stage, bass light. Blech!
https://www.ebay.com.au/itm/EARPAD-FOR-HD400-410-414SLM-PK2-SENNHEISER/272461321916?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649