Many Sennheiser headphones have 3 small bumps on the left earpiece near where it connects to the headband. That makes it easy to tell which way the headphones go without having to look at them. You can just feel for the bumps.
Pet Peeve -- why do headphone companies make the LEFT and RIGHT symbols so hard to locate
I can often be found staring and squinting at my headphones and IEMs, turning them around and around, looking for the Left and Right symbols. Most are tiny and in the same dark color as the housing. Some are outside, some inside, and for some headphones, don't even exist (I am complaining about you, Sennheiser PC38X).
Why do the manufacturers make these important labels so small and hard to find? Aesthetics? Arrogance? Lack of human factor design skills?
Why do the manufacturers make these important labels so small and hard to find? Aesthetics? Arrogance? Lack of human factor design skills?