Hey Jim,
The K501 us an open headphone. It was AKG's main audiophile phone for many years until it was updated to the 601. To my ears, it's a detailed but smooth sounding headphone. Like I said, it doesn't have the greatest bass impact with most amps but it's great with classical and jazz. Nice soundstage too. I consider all AKG's to be among the most comfortable headphones to wear for long periods of time too.
For you guys who are new to the headphone scene, don't discount that last bit about comfort. The last thing you want is to have to stop listening because of comfort issues. I do think that headphone manufacturers have made some real strides is this area lately but that isn't universal.
There are things you can do to make them more comfortable. Some of it depends on how you plan to listen to them. In other words, if you're planning to be active when you listen, they can't be so loose that they're going to fall off your head.
Here's a short list of comfort mods.
Reducing the HD600/650 head-clamp (applies to most headphones that squeeze your head till your eyes bug out).
First, extend the headband about and inch away from it's most extended position (as if you had an enormous head). Take some books and put the headphones on them and add another book or more so they're pretty tight. Leave it like that overnight.
The idea here is to train the inside end of the metal band inside of the headband so it's not so tight.
Check the fit. If it hasn't loosened at all, add more books and repeat.
Then, adjust the headband to your optimal size and follow the above procedure again.
If you have a pretty big head, you'll need to do this several times while adding books each time.
Some headphones have thin padding on the earpads. If your ears touch the driver at all, it'll hurt after a long listening session. There are a couple of different tactics you can try.
If the earpads have a flap on the driver side of the material covering the foam inside, you can cut some open cell foam (about 1/4-1/2" thick) and slip it under the flap.
Some folks swear by using rubber tubing rather than foam.
In cases where there's no flap, you may have to remove the earpads and insert the "spacer" inside or under the pads. Most pads are attached with some sort of adhesive but with some, you have to take the earcups apart to free the earpads.
Easy does it with this. You don't want to crease the headband metal at all or fatigue the metal.
* Be aware that the space between the driver and your ear is an integral part of the design, like your listening room, so changing the basic dimensions by adding too much foam will change the frequency response.
That and where you locate circumaural earpads/earcups in relation to your ear is somewhat like moving your listening chair back and forth in relative to your speakers. Many headphones sound better when the earcups are located a little closer to the front of your ears than exactly centered. It's always worth experimenting.
