AIWA HP-M16 headphone specs?

[evcco]

I've had these little portables in continuous service for nearly 25 years now (for various walkmen, discmen, computers/laptops, and occasionally even used as a microphone) and, with the odd repair, are still working as good as new. Needless to say, after such long use my listening preferences have been largely attuned to them and, rightly or wrongly, they are still the standard I use to judge any other headphones by (including full studio models). Unfortunately I lost any specification documents (if I ever had any) decades ago and can't seem to find any online, so I'm just wondering what's actually going on in those little drivers, and how they would compare to similar models (such as the much ballyhooed Koss Portapros).
 
Thanks for any help/info in advance...

 

[evcco]

http://bartman88.blogspot.com/2016/10/aiwa-hp-m16-headphone-specs.html
 
Type: open-air dynamic stereo headphones
Driver units: 32mm diaphragm
Impedenace: 32 ohm
Sensitivity: 97 dB/mW
Rated power: 40mW
Maximum input power: 100mW
Frequency response: 20-20,000Hz
Cord: 1.1 meters (43 inches)
Plug: 3.5mm stereo plug
Weight: 40 grams (1.41 oz) (w/out cord)
 
Thanks Bartman (...no thanks Head-Fi community [...just kidding {...kind of}])!
 
However, as noted in the link these specs were apparently from 2003. My pair are from about 1992. I didn't know they were around for so long, if not longer... Anyone know when they were first produced, or if the specs could have changed in the meanwhile? The figures listed above seem fairly unimpressive (not that specs alone always tell the whole story). Might they have been cheapened somewhat when Sony bought-out Aiwa in 2002?
 
Don't let me down again Head-Fi (...just kidding [...kind of])!