This questions pops-up on the forums occasionally. I believe you will see all types on the R&D and Operations side - just as you will with any electronic product. Most people think only of the "sound engineers", but the reality is that is just a small part of the puzzle. Here's just a few I can think of...
- Overall product design
- Detailed design of individual parts like cups, headband, pads, etc, etc
- Specs & sourcing of each component material (someone has decide exactly how thick the pleather in the headband will be)
- Fabrication & assembly processes
- Assembly & test jigs
- Establish the overall vision for the product
- Own the target market the product will address
- Establish the design goals and cost targets
Also, Quality, Compliance, Testing, etc, etc
Even if we talk only about those folks that do specific R&D tasks like selecting the drivers and tuning the sound by tweaking cup size, materials, porting, damping, etc - I think looking at the backgrounds of the folks in the industry will show you that they are pretty diverse. At most manufacturing companies, the "designers" weren't trained to do that job - they earned it after many years in a particular product segment. I'll bet you will find some folks with audio engineering degrees, but I will also bet you find many with degrees in electrical/electronic engineering, mechanical engineering, physics, or even non-technical degrees that sort of just fell into the job. Then, there is also all the technicians & factory workers that might have received general technical training, and the rest was learned by OJT.