[Seidhepriest]

...have just made their way off the flea market for the equivalent of US $15.
 
Initial impressions: easily the most balanced Denon headphones for electric guitar/rock/metal/etc. Resolution is lower than AH-P372, but the AH-P372 have those awful peaks in midrange that invoke a lot of crackle and shoutiness (AH-P372 have a very irregular frequency response also, it's like a ride up and down). So overall the old AH-D210 sound is more natural/balanced, and the soundstage is larger. Modded AH-D310 outperform them of course, but the classic thing is interesting. They're also semi-open, unusually for Denon headphones which are commonly closed.
 
There's still that congestion, lag and dead harmonics of a stock cable. But really they outclass AH-P372, and that's all the fancier since my AH-P372 are heavily modded. Surprisingly, the foam has not decomposed (this is an old model from the 90s, if not late 80s). Aside from a few scratches and slightly faded print they don't look that bad, even.
 
Photos later.

 

[Seidhepriest]

As promised...
 
 

 

[Seidhepriest]

And now for something completely not different...
 

 
- Foster 022096, from the 2011 OEM catalogue. Denon AH-D210 look like a straight implementation (of an older version of course). Official specs are "32 ohm", but they sound like 44 ohm. They also wear out a player's battery sooner (that confirms the higher impedance). Overall they're better balanced than their new iteration the AH-P372. Sound-wise they're slightly slower, slightly duller, slightly "stiffer" (higher impedance) and the resolution is slightly lower than AH-P372 or AH-D310. But because they're a lot better balanced than the AH-P372 (which have a roller-coaster frequency response even after damping and recabling), and better-balanced than the AH-D310, the overall impression is a lot nicer. A pocket player drives them loud no problem, muting all street noise. They're semi-open (or semi-closed, depending on your life's perspective ), with taped vents (similar to AKG K-240, Roland RH-50, etc.).
Long story short, these are the long-lost elder (and in some ways superior) sibling to modern Denon headphones. You see, the low impedance/fast dynamics of current models make them "leap over midrange". AH-D210 are a lot more midrangey.

 

[Seidhepriest]

There're places on the 'net where people ask how to replace the worn-out pads and headband on those, and another poster who says he couldn't get replacement cushions from Denon for this discontinued model. Which is silly as the headband and pads from AH-P372 fit (AH-P372 pads are even nicer, with larger holes). Yamaha RH5MA parts might fit also. Other similar-sized supra headphones' pads ought to fit (e. g. Technics RP-DJ-100, Sony MDR-X-150, MDR-ZX-100, etc.).

 

[Seidhepriest]

Mmm this is curious, they really are closer to AH-D310 and they resolve vocals a lot better than AH-P372.

 

[Damage]

Oh, I remember those.  Those were my first "fancy" headphones, ever, some 15+ years ago.
 
The only thing I really remember about these was that they were nothing special.  I'd love to hear them these days to see if my judgment on these were correct or not, but comparing the current sets they'd go up against, I'd say that my memories about them would probably be correct.  I think the cables were crap on these too as well.

 

[Seidhepriest]

They're superior to the new AH-P372, heavily modded. Blu-tack+recable and they're getting up there with the modded AH-D310. Slightly coarser, not as ambiental, being supra, but modded they have The Tone for guitar music. Which is a bit uncommon for newer Denon models (AH-D1001/Creative Aurvana Live are guitar cracklers).