Trying to recable my headphones but I'm stuck, need help (pics)

[Allswell]

Hello,

I've decided to learn how to re-cable headphones and for fun I'm trying to re-cable an old pair of Sennheiser HD 449 headphones.

I bought a new cable for them, a Mogami W2893 recommended via this guide I'm trying to follow: https://www.instructables.com/id/Quality-DIY-headphone-cable-replacement/

But I'm stuck and need some help.

The instructions in the guide specify to group and solder together the clear, black and copper shielding of the Mogami cable to create a ground (for the 3.5mm stereo jack that I'll be using) but what about the other end that connects to the headphones? As the headphone end has three wires that need to be connected, left, right and "com". What is "com"? is that the "ground" (clear, black and copper shielding part? from the jack end?).

If someone could clarify that would be much appreciated.
(Please see attached pictures)

 

[JeffS7444]

What is "com"? is that the "ground" (clear, black and copper shielding part? from the jack end?).

Correct.

 

[AnalogSteph]

These phones are a bit of a stupid design. Normally you want a 4-conductor cable to carry L and R ground return separately right up to the plug. They didn't do that and merged L and R ground return into one on this circuit board, so that they could use a 3-conductor cable. Somehow I doubt that the ground return resistance of that cable is less than 0.32 ohms (no more than 1% of nominal driver impedance shared makes for a good rule of thumb for an acceptable level of crosstalk).

Unless you can combine two wires and the shield from the new cable to give sufficiently low resistance, you will have to either cut or eliminate this circuit board altogether, so both ground returns can be carried separately.
According to Mogami, W2893 shield resistance is 0.025Ω/m(0.0076Ω/Ft), and each conductor weighs in at 0.13Ω/m(0.040Ω/Ft), so that would be 18 mΩ/m or about 1.77 m (~6') maximum length, not taking jack/plug contact resistance into account.

 

[Allswell]

These phones are a bit of a stupid design. Normally you want a 4-conductor cable to carry L and R ground return separately right up to the plug. They didn't do that and merged L and R ground return into one on this circuit board, so that they could use a 3-conductor cable. Somehow I doubt that the ground return resistance of that cable is less than 0.32 ohms (no more than 1% of nominal driver impedance shared makes for a good rule of thumb for an acceptable level of crosstalk).

Unless you can combine two wires and the shield from the new cable to give sufficiently low resistance, you will have to either cut or eliminate this circuit board altogether, so both ground returns can be carried separately.
According to Mogami, W2893 shield resistance is 0.025Ω/m(0.0076Ω/Ft), and each conductor weighs in at 0.13Ω/m(0.040Ω/Ft), so that would be 18 mΩ/m or about 1.77 m (~6') maximum length, not taking jack/plug contact resistance into account.

Wow, thank you for such a detailed reply but I did not understand any of it at all unfortunately.

I replaced the cable but seem to be having some issues with the right channel... (no sound comes through unless you wiggle the 3.5 mm jack...)
So I guess I have to open up that jack connection and see what's happening. I could've sworn I soddered everything nicely.

 

[Allswell]

Ok, the issue has been resolved.
It looked like it was a matter of solder points touching each other when I wrapped everything up.

So I wrapped those points (wire connections) up with electrical tape and all is well now.