Soldering The Shield Wire

[rlyach]

I have been going over the instruction for building the headphone cable and was curious about the fact that the shield (ground return) is not soldered. Will this mechanical connection degrade over time?

Also I was curious about the damping used in the driver cups. Was this an attempt to change the resonant frequency of the enclosure? I found this very interesting. I will have to listen to the headphones out of the box first, then with the cable, and finally with the damping modifications. I may dampen one only to hear the difference of a damped and undamped enclosure. I am very excited to get my Crack and the phones working.

 

[jboehle]

I would solder it. I was not very happy with the final connection made with the shield the way the instructions said to do it. I screwed up the 3.5mm end of my cable with the glue heat shrink (just aesthetics, it functions fine), so when I redo that end of the cable I am going to both solder and crimp. Solder for a reliable connection and crimp to provide strain relief. If you do that and choose not to use the tech flex, you really don't need to use the glue heat shrink at all.

 

[jboehle]

Also see this: http://bottlehead.com/smf/index.php/topic,6225.0.html

 

[rlyach]

Thanks jboehle, I have some things to think about before I actually build this. I have built a lot of cables for audio recording equipment including microphone cables, patch cables, and instrument cables, and I have always soldered the shield. I had not considered leaving off the tech flex. I like the look and it adds to the durability of the cable. I have used it for some of my instrument cables. Even Tube Depot instruction videos for building guitar cables use tech flex. I understand that there have been a few comments stating that the noise of the cable moving can be heard through the headphones.  I will have to weigh my options. Thanks for your post.

 

[Paul Birkeland]

Crimped cables are actually quite a bit more common than soldered cables.

Nearly all coax that you would buy or use for your cable TV and high speed internet, for instance, would have crimped connections on each end.

When you combine the crimp with the very sturdy heatshrink we provide, the connection will last quite some time.  If you want to solder, just be sure you don't solder so much that you can't get the plug back together.

-PB

 

[jboehle]

I find that coax crimp connections are much easier to apply just because of the physical layout with the connector, the shield has nowhere to go, as it's completely surrounded by the connector.  The connectors in the Crackheadphone cable I had problems with because there is nothing fixing the shield in place to the cable jacket.  That combined with the physical layout of the crimp/connector, it was very hard to get the shield and cable jacket to stay in place while crimping it.  When applying pressure, the jacket and/or shield want to move.

That may be because I just used needle nose pliers in various positions to crimp these?  Is there some more specialized tool that makes better crimps using these types of connectors?

 

[mcandmar]

It is a bit of a fiddle, i found that cable more challenging to assemble than the amp

 

[jboehle]

Ha, I found the burnishing of the metal tape to be the worst part of the whole thing.  That took freaking forever!  Maybe I was just being too anal about it.

 

[Doc B]

Burnishing the tape is simply to make sure that it is in contact with the plastic as much as possible. The stuff is sticky as heck, so it should be a doddle as our UK friends say.

The tape creates a constrained layer of damping material. The sticky synthetic rubber between the aluminum and the plastic of the ear cup is the constrained layer. The tape doesn't change the resonance frequency much, it mostly damps the energy imparted to the cups by the speaker. You can tell what it does by tapping on an untreated cup and a treated cup with your fingernail.

It doesn't have to be pretty or perfect, it just has to stick.

 

[rlyach]

Thanks for the explanation Doc. If I understand you correctly, it changes the ratio of the mass of the cone and voice coil to the mass of the cup, making the speaker a little more efficient, especially at lower frequencies. This might be similar to speaker cabinets using dense laminates. I assume then that the felt is used to absorb internal acoustic reflections, removing phase distortion.  Do I have this right?

 

[Doc B]

It's just constrained layer damping. The excitation energy of driver that is transferred to the plastic ear cup goes into the lossy synthetic rubber. The constraining layer of aluminum over the rubber causes the energy to be dissipated by shear deformation of the rubber. As far as I know all that is happening is you hear less of the cup vibration and thus the sound of the actual driver is masked less, sounding quicker and more concise.

It is in fact rocket science. The constrained layer damping tape we supply is used to line aircraft, rocket and submarine fuselages. I had to buy a whole case of the stuff. $$$$!

 

[rlyach]

Thanks for the further clarification. I did a search on "constrained layer dampening" with headphones and speakers and got several good papers, including a reference to a book, "Loudspeaker and Headphone Handbook." After reading this information I finally understand the changes the kit makes to the driver enclosures. Essentially, you only want to hear the driver vibrating at the intended frequencies, and you don't want to hear the enclosure at all. Therefore it is important to keep the ear cups from vibrating and adding other frequencies to the sound. Sorry for all the questions, I like to understand what I am building and why.

 

[Paul Joppa]

Randy, you got it. The other way to do this is to increase the mass of the enclosure - Blumenstein fans will recognize this in their change to thicker Orca enclosures for the top of the Orca line. But inch-thick solid bamboo earcups are not practical as you can imagine!

 

[Doc B]

Tell that to some of the other manufacturers. I keep waiting to hear one of them gets sued for neck strain.

 

[mcandmar]

Tell me about it, my new Hifimans are half a kilogram!    Took some getting used to after the feather weight mahogany Ms-Pros.