Tofty Headphones 4: Aurorus Borealis Inspired

I present my remix of the Aurorus Audio Borealis/Australis inspired DIY Headphones.
As of the 24th of January 2022 all files have been updated and there are two versions of this design:
TH4A is the original version and is the red and blue model in the above photos,
TH4B has a redesigned headband and is the silver and black model in the photos.

The major change in my design is the addition of a second set of connectors at the rear of the earcups, which allow the use of a removeable bridge cable.
This means that the headphones can be used with either a split cable, without using a bridge cable, or with a single sided cable that can be plugged into either side, with the bridge cable installed.
However it can also allow the headphones to be converted to wireless, relatively neatly by using a Bluetooth Receiver and a 3.5mm TRS jack wired into the bridging cable.

There are printed Conn Mounts designed to take three different connector types (see photo above):
Mini XLR male external screw in connector,
3.5mm TRS Jack female external screw in connector,
3.5mm TRS Jack female internally installed with external securing nut.
There are also versions of each of these Conn Mount parts that are only single sided and don't take a second connector; for builds that do not plan to use the bridge cable.
This means there are six different Conn Mount options.

The cable clips for the bridge cable are designed to take cables with a 4mm diameter. If the cable used is narrower then some strategically placed head shrink sleeving can be used to make up the difference.
There are different versions of the Forks and Band Clamp parts; some that are designed for the bridge cable and others that are not.

The headphones can be built as either open-back or closed-back, using either the Outer Ring or Outer Cup parts respectively.

It is advised to check either the .STEP or Solidworks files for both the TH4A and TH4B versions of the headphones, to help identify all the different possible arrangements and which one is most suitable.

TH4A Specific Parts.
This is the original version, just with some parts tweeked to slightly improve them.

Parts Required (other than printed parts):

1x Beyerdynamic metal head bow (https://www.showcomms.com/beyer/beyerdynamic-dt990-headphone-spare-parts/beyerdynamic-dt770-metal-head-bow-973361.html)
4x Silicone O-rings 8mm outer diameter, 2mm cross section (https://www.ebay.co.uk/itm/323973430027),
1x Hifiman replacement headpad (https://www.ebay.co.uk/itm/402514745517),
2x Aluminium M3 x 60mm round standoffs, 5mm diameter, black (https://www.ebay.co.uk/itm/224732554360, 70mm ones felt too long),
4x F3-8M thrust bearings (https://www.ebay.co.uk/itm/273954352288),
8 x M5 1mm thick nylon washers (https://www.ebay.co.uk/itm/401506514600),
2x 100mm ear pads (probably worth getting a few and seeing how much they change the sound),
100x100mm of fine stainless steel mesh (I used #120 mesh and it looks about right, ebay),
2x 50mm dynamic drivers (the Peerless by Tymphony HPD-50N25PR00-32-ND drivers are desirable, as they are the drivers both Aurorus and Kennerton use in some of their headphones, but they are currently out of stock from Digikey. Other 50mm drivers can be used, but will require a different Driver Clamp and Driver Spacer part),

Fixings:
2x M3 x 18mm Countersunk Hex A2 screws,
2x M3 x 5mm Knurled Thumb Screws (https://www.ebay.co.uk/itm/164838535376)
4x UNC 4-40 x 3/16" Socket Head Hex A2 Screws,
30x UNC 4-40 x 3/8" Socket Head Hex A2 Screws,
6x UNC 4-40 x 5/16" Countersunk Hex A2 Screws,
4x UNC 4-40 x 5/8" Countersunk Hex A2 Screws,
10x UNC 6-32 x 1/4" Countersunk Philips Black Panel Screws (https://www.ebay.co.uk/itm/302136416433, panel screws have a smaller countersunk head than normal screws. These screw into a very shallow blind hole, which should be tapped using a 6-32 bottoming tap),
2x UNC 6-32 x 3/16" Countersunk Philips Black Panel Screws (for the BT Holder part).

TH4B Specific Parts.
This is an updated version, which uses a different design of the Band Clamps and Forks to change the way the earcups swivel and hopefully improve the way they sit on the head.
I would recommend this version of the design, as I think it is a significant improvement.

Parts Required (other than printed parts):

1x Beyerdynamic metal head bow (https://www.showcomms.com/beyer/beyerdynamic-dt990-headphone-spare-parts/beyerdynamic-dt770-metal-head-bow-973361.html)

4x Aluminium M3 x 55mm round standoffs, 5mm diameter, black (https://www.ebay.co.uk/itm/224732554360),
8 x M5 1mm thick nylon washers (https://www.ebay.co.uk/itm/401506514600),
2x 100mm ear pads (probably worth getting a few and seeing how much they change the sound),
100x100mm of fine stainless steel mesh (I used #120 mesh and it looks about right, ebay),
2x 50mm dynamic drivers (the Peerless by Tymphony HPD-50N25PR00-32-ND drivers are desirable, as they are the drivers both Aurorus and Kennerton use in some of their headphones, but they are currently out of stock from Digikey. Other 50mm drivers can be used, but will require a different Driver Clamp and Driver Spacer part),

Headpad Options:
1x Hifiman replacement headpad (https://www.ebay.co.uk/itm/402514745517),
1x Beyerdynamic headpad (https://www.ebay.co.uk/itm/124639450695),
There are also two printable headpad options available.

Fixings:
4x M4 x 6mm nylon or nylon tipped grub/set screws (https://www.aliexpress.com/item/1005001634610309.html)
8x M3 x 10mm Countersunk Hex A2 screws,
4x UNC 4-40 x 3/16" Socket Head Hex A2 Screws,
30x UNC 4-40 x 3/8" Socket Head Hex A2 Screws,
6x UNC 4-40 x 5/16" Countersunk Hex A2 Screws,
4x UNC 4-40 x 5/8" Countersunk Hex A2 Screws,
10x UNC 6-32 x 1/4" Countersunk Philips Black Panel Screws (https://www.ebay.co.uk/itm/302136416433, panel screws have a smaller countersunk head than normal screws. These screw into a very shallow blind hole, which should be tapped using a 6-32 bottoming tap),
2x UNC 6-32 x 3/16" Countersunk Philips Black Panel Screws (for the BT Holder part).

There is a third headband option which doesn't use the Beyerdynamic headband bow and is instead 3D printed. It can be found here: https://www.thingiverse.com/thing:5201999

Optional Parts for both TH4A and TH4B versions, depending on chosen arrangement:

Anker Soundsync A3352 Bluetooth Receiver (this is the model I choose and designed the holder around, but there are many others available),
4x Mini XLR male socket connectors (TA4M, https://www.ebay.co.uk/itm/263727125824, I'm using cheap ones but the proper ones are from Switchcraft. These require the holes for them to be drilled and tapped for a 7/16"x32 UNS thread),
4x 3.5mm TRS female panel mount jack connectors, external screw in type (https://www.ebay.co.uk/itm/351607508978, These require the holes for them to be drilled and tapped for an M8 x 0.75mm thread),
4x 3.5mm TRS femal panel mount jack connectors, internal mount with external nut retention (https://www.ebay.co.uk/itm/255207460125),
3x Mini XLR female plug connectors (TA4FX, enough to make one split cable and one non-split. I'm using 4 pin connectors as I will wire up the headphones to allow for a balanced cable to be used, wiring diagram to follow),
2x Cable Technologies low-profile right angle Mini XLR TA4 female plug connector (https://www.wendysbroadcast.co.uk/broadcast-audio-products/?get=Low-Profile-Connectors/Low-Profile-TA4-and-3.5mm-LJ/Low-Profile-TA4-Female-with-Black-Cap-(5mm)&ct=vpt&id=2592),
Alternatively, I've made a part which helps convert a normal female plug connector into a low-profile right angle version: https://www.thingiverse.com/thing:5223748 ,
2x 3.5mm TRS male audio jacks (for the far end of a cable, plus one more to make a wireless bridge cable),
Cables should either have 3 or 4 wires, depending on whether you plan to make a balanced or unbalanced arrangement.

This is how I wired up the mini XLR 4 pin connectors:
1 - Left +
2 - Left -
3 - Right +
4 - Right -

The standard 3.5mm jack wiring arrangement is:
Tip - left +
Ring (middle) - Right +
Sleeve (base) - GND (left & right -)

(need to add a wiring diagram)

I would like to thank the following Thingiverse and Reddit users for sharing their ideas and files so freely:

u/mwildebeast (Reddit) - This all started due to them posting their initial design up on Reddit and inspiring me to want to make one myself.
sleepdeprecation (Thingiverse) - Their budget friendly headband design helps the headphones stand out even more.
u/Meteroson (Reddit) - The F3-8M thrust bearings they added to their build were new to me, but I'm glad I was made aware of something so useful.
VasilyevichDrago (Thingiverse) - Their redesign included a great many changes from mwildebeast's original, but pretty much every single one had merit and I just couldn't not integrate them into my own redesign. Great work.
RodediahK (Thingiverse) - Adding O-rings to the headband adjustment was a really neat addition.

Remixes are encouraged. Please share any ideas you may have on this project with the community; by using the REMIX button on your upload.
These CAD files were created with Solidworks.

Only for non-commercial use. Since this design is very close to the Borealis/Australis headphones from Aurorus Audio; any commercialised use of these files may have the potential to leave one open to legal action.

I hope you find my work of interest.