The scope of this article will be to show some of the many modifications you can make to alter the sound of your headphones. In this example I will show how I did this to a pair of JVC HA-RX700 headphones, but most of the mods can be applied to any full-size headphone. I will not guarantee that ANY of the mods described here will alter the sound in a positive way. Also, be advised that you will risk damaging your headphones, so if you are not entirely sure what you are doing (or cannot afford to replace them) you should probably not try to do this.

The mods

Some time ago I bought TWO pairs of headphones in a single go. "Why?" you may ask... well the JVC HA-RX700 had been receiving a lot of hype on the internet for their great value. Yet the bigger brother, the JVC HA-RX900 was supposed to be even better (though at roughly double the price). Now, since apparently I had way too much money on hand I went ahead and bought both pairs on a trip to the US, just to try them out (and since they were near to impossible to locate in Denmark).
OK, so I got both phones and took them back for closer listening).
After proper "burn in" of both phones I must admit I really liked the HA-RX900 better and thus the 700's were sentenced to a still life in a drawer. Not long time ago I decided to re-visit these phones and since I still found them inferior in sound quality to the 900's I decided to go ahead and MOD THE HELL OUTTA' THEM PHONES!!!111

First, disassemble the headphones, if this is too much of a task or you are not entirely sure you can remember how to REASSEMBLE them, STOP RIGHT NOW or continue ruining your headphones and cry later!
First point of concern, the large surfaces made from thin-as-hell plastics MIGHT resonate and totally ruin sound quality, though my engineering background tells me that is probably not the case. Whatever, we all fully well understand that common sense is definitely NOT widely aknowledged in the world of HIGH FIDELITY.
Next point of concern is the cabling which seems to be thinner than a bad case of diarrhea. We surely cannot have this, bigger cables equals BETTER CABLES. Looks like we will have to RECABLE these phones!

First I removed the very outer shell of the phones. Inside I found a small piece of foam I can only guess was put there to keep the parts from rattling (though the snaps were so firm that would probably never happen). The foam is the small round part in the middle. I decided to help that foam doing its job, so I put 3 dabs of profiled foam-tape on the outer shell to put pressure on the inner shell ribs. To keep the large surface from resonating I applied 3 small strips of sound deadener to the surface. I have read only 25% of a surface needs to be covered to achieve good resonanse dampening, but it just looked WRONG.

Off with those puny small strips of sound deadener and on with some BIG-ASS pieces...

...and NOW we're talkin'!
Next thing, put the foam back in place and press the outer shell back in place.

Moving on, I did the same to the "inner" pad (the one holding the driver). This was a bit more of a work since I had to cut all different size sound deadener the get good coverage. I think it is safe to say I succeeded.

Now go and prepare the wiring you will be using for your headphones onwards. I chose UTP cabling since it is cheap and comes paired and twisted and since it seems to have a bigger crosssectional area than the original wire.
Oh, the cable sleeve is homemade from "tile string"

I now put the new wiring in and this is where you have to plan a bit ahead...
The wire for the left driver should be cut shorter than the wire for the right driver since the wire for the right driver will have to be led over the headband and into the right cup. As crazy as it may sound I think JVC put in 90cm of wire for this task, but as I am not going to risk standing missing 5cm's to complete the job I did the same...
In the middle of the picture you can see the inside of the "sound chamber" opposite to the driver. I applied some drawer liner to this surface to stop unwanted reflections, and to the right you see a piece of foam I put there to help tighten up the bass a little (I have never been much of a "bass-head").

Since the original cable was about half the size as the new one, I had to route the new cable out along the other hinge on the phone. To do this it was necessary to drill a small hole as you might see. At this point it gets rather tricky as you will have to get the wire through the headband and out on the other side. Also, since the existing route was too small for the new cable I also had to drill a small jole here to get the wire in. In order not to have white/orange wire running visibly I put black heatshrink on the part that might be visible.

Finally through the headband and starting the reverse procedure to reassemble the right hand cup. You can see a layer of felt covering some of the driver, I carefully peeled most of it off.

Now solder your new AND BETTER cable onto the driver (like you did on the driver on the left hand, I mean you DID REMEMBER that, right?). Please notice the drawer liner and foam in the inside of the cup.

After assembling your phones you should have something looking like this. Now lets move on to terminating that cable and get to the good part (that is actually LISTENING TO MUSIC egghead).

Of course you wrote down how you put in the wires, didn't you? In case you did soldering everything together (i do not mean that literally) should be no problem. Pull the cable sleeving away to get some bare cable to work with and start soldering.

After soldering pull the sleeve back over the cable, apply your prepared heatshrink and screw the plug together...

Like this.

A picture of the discrete cabling inside the hinge...

...and the spot where the wire goes into the headband (it is on the upper left).

Congratulations, only one mod left (might even be the one that does the most for the sound).

Yup, have a whisky and put on some of the music you love...

"What did this do to the sound then?" you might think... Well, I am not going to go into this whole appraising rant telling you stuff I really am not qualified to, instead I will say that these phones are now actually able to go onto my skull and sit there for hours whilst I listen to music. Everything now seems to be like it should be, so there has definitely been an improvement. I do not prefer these over my Sennheiser HD600's, but I haven't felt the need to put these away and put on the 900's like I did before.