is there a way to mod or add something to make the treble more forward? i tried transfering the drivers with an old gaming headphone with open back, the bass response and mids are perfect (reference) but the highs are seriously near inaudible.
and is there a material thats super cheap that can lessen reverb from plastic cups? will ordinary cotton work, or cotton fabric for pillows? Dynamat is too expensive and not availble in my area.
There's a few things you can try.
1. You can perfect the sound with EQ. I am treble sensitive, so I EQ almost everything I own to either cut treble on overly bright headphones, or boost certain frequencies to get the sound I want.
2. You can also switch the pads to velour pads. While this won't "boost" treble like an EQ can, it WILL reduce bass (effectively changing the sound to seem somewhat brighter). This is why most open (neutral) headphones use velour pads, and why people often complain that open headphones have "too much treble".
3. You can play with the vent holes on the driver, tuning the sound. Cover up 1 or more holes (using tape, modeling clay, or Bluetac) and see if you like the change; uncover 1 or more holes and see if you like the change. I tune many of my headphones like this. Generally, holes that are on the back of the MAGNET control bass; the holes around the outside control treble and midrange. Here's some photos so you get an idea of what I'm talking about (click for larger view):




4. If the headphone has anything in between the driver and your ear (felt, fabric), you can remove it to allow more treble through to your ear. These things are added to slow high frequencies, and removing them will improve clarity, make the headphone sound less veiled, and almost always brighten the treble.
As far as material to dampen reflections on the cheap, use the foam rubber from a computer mousepad. You can buy a generic mousepad for under $1. Peel off the thin fabric layer, so all that you're left with is a hunk of rubber. Then trim it to shape with scissors, and attach the mousepad rubber to the inside of the headphone cup using glue.
You can also use adhesive-backed foam, available in rolls at any hardware store. It's used for weatherstripping applications, costs a few dollars, and looks like this:
The adhesive is very weak on some of the adhesive-backed foam rolls, so test it out in the store to make sure you get one that is very sticky. And clean the plastic of the headphone cup using alcohol really well (letting it dry) before sticking the foam on so it sticks well.
Hope that helps,
- Slater