The three different drivers of the AKG K500Some photos so you can identify which version you have, and which versions have been measured on this site. If you take off the pad and hold the headphone in front of strong light it's easy to tell which driver it is.
The first one, as presented in the AKG introduction brochure, had a half matte diaphragm and 12 openings at the back of the driver (dampened with white fibre paper). All metal plug and adapter, and somewhat thicker cable.
The second, and most common version (and in my mind the best, although I haven't experimented much with version No 3), had a half matte diaphragm but only 2 + 2 holes at the back of the driver. All metal plug and adapter.
On the diaphragms above, there are two types of ridges combined: short ridges at the rim, longer ones at the centre.
The third version had 2 + 2 holes at the back of the driver, but a clear diaphragm with a simplified ridge pattern: only long, single ones. The cable was the same as the above, later a partly black plastic plug with metal adapter and slightly thinner cord as on the K401 and K501 headphones.
K500 (grey) and K501 pads (black). The latter has a foam rim gasket, the K500 not.
I was lucky to grab a near mint first version K500 a couple of years ago. This one was also equipped with a removable foam filter which tames the treble somewhat.
[Edit: come to think of it, these filters could have been from the K500 with clear diaphragms, the third version, and if so a late attempt to solve a problem. Difficult to keep track of all these versions!]
