Designing and 3D printing replacements for broken Bose headphones
A project by:
Gabriel B. Soares
June - July 2015
During one of her trips from NYC to DC to visit me, my friend accidentally dropped her Bose headphones and broke one of the plastic pieces that holds the earpiece to the headband. These headphones (Bose QuietComfort 2) used to belong to her father and have probably been in use for nearly 10 years now. They still produce a great sound, and the electronics are all intact, so I told her I would try and fix them.
After searching the Interwebs, I wasn't able to find anyone who sold the components I needed to replace. Reading through forums, I found that many people had also broken their Bose headphones in the exact same location, and that this was in fact a fairly common mode of failure. Bose does not sell any replacement pieces, and instead has a program in place where they will give you a discount on your next purchase if you trade in your old, broken headphones.
Since she didn't want to spend $250 on new headphones I decided I would try and design the pieces and 3D print replacements.
Assessing the damage:
The first thing I did when I got a hold of the headphones was to examine what had broken and what would require replacement. As the following images show, the plastic band on the left earpiece broke near the section that attaches to the headband, whereas the right piece looks intact. Upon further investigation, however, I found that the right piece was also starting to develop cracks and it would just be matter of time before it broke in the exact same manner.
These pieces are made out of ABS and have some fairly complex designs/attachment mechanisms which I knew were going to make my life extremely difficult. The connection between the headband and the earpiece is slotted so that the ear can rotate ~10º in one direction and ~100º in the other. The back side of the piece has a channel through which runs the wire that connects the right and left earpieces together. The tabs that connect to the earpiece are keyed so that they can't be accidentally swapped (can't swap right and left plastic attachments) and so that the earpiece can pivot.
The disassembly of the Bose QuietComfort 2 was easier than I expected.
I began by removing the cushions on the earpieces and cutting out the cushion on the headband (I threw them out since these were old and needed to be replaced anyways). I will eventually buy a replacement set for these from Amazon.
I then proceeded to remove the screws that connect the headband to the plastic piece I am 3D printing.
I then removed the four screws located inside the earpiece that attach the silver plastic casing to the headphone (this exposes the PCB and electronic components). With the PCB exposed, I could then unsolder the 3 connections of the wire to the PCB. I made sure to make a note of which wire connects to which copper pad. In this headset you can see that the red wire is connected to pad with silkscreen "7", the copper wire to the pad with silkscreen "8", and the green wire to the pad with silkscreen "9".
First design iteration:
The goal of the first design iteration was to get the correct contour shape and match it to the original piece. Getting the dimensions was a challenge and required me to get creative with my set of calipers. I began by tracing the contour of the plastic piece on paper and using that to try and get precise measurements (first image below). However, I wasn't very satisfied with this approach as it would mean that I would have to recreate the contour in Autodesk Inventor through the use of splines and would make it difficult to make adjustments if I needed to.
What I did instead was to measure the dimensions of the elliptical earpiece itself (length of the major and minor axes), offset it to get the size that I needed, and remove the lower section that I didn't need. With this approach, if I later found out that the fit wasn't quite right, I could simply change either the dimension of the ellipse or the offsets, and those changes would propagate through the subsequent steps in my design.
As I moved along with the initial design, I would print test pieces to make sure that I was within tolerances. My first print was to check that the elliptical shape matched that of the original piece. The second print was to check the height and draft angles of the side walls. The third print was to check the alignment and diameter of the circular tabs which secure the connection to the earpieces (second image below: from bottom right, counter-clockwise).
Once I had the overall shape of the plastic piece, the next step was to begin working on some of the details on the tabs which allow the earpiece to pivot within a limited range of angles. For this print I tried using a slightly higher-quality PLA filament available at the Techshop since I wasn't obtaining good results with my spool of clear filament (I ended up using neon yellow).
Second design iteration:
The next step in the design process was to work on the tab that mates to the headband, and the channel through which runs the wire. Getting these just right took a significant effort and a few test prints to get right.
Just like the connections to the earpiece, the tab which connects to the headband is also keyed in a particular way so that rotation is limited over a specific range. This meant that I had to spend a long time trying to figure out what the angle was and how I would be able to print the piece.
I also had to hollow out a channel through which to run the wire that connects one earpiece to the other.
Because of the hollowed-out sections, I had to print these test pieces with the help of support material, which meant I also had to spend a long time after the print was completed removing that material and cleaning it up. For future prints, I might look into finding a place that can do either SLA or Laser Sintering printing processes that might help get higher quality results. For the prototyping phases where I am just trying to check rough design, I'll have to stick to printing PLA on the MakerBot.