Most modern phones are supplied with a 4 pole headset these unlike standard stereo connections also have a 3rd black ring on the tip of the jack to allow for hands free actions or to carry a microphone signal. Using a standard stereo splitter with these headphones can cause issues and so a 4 pole splitter is required.
Split a 4 pole output to two 4 pole headsets Perfect for sharing music with friends with one device 15cm in length Gold contacts
PLEASE BE AWARE THAT MIC/VIDEO AND GROUND CONNECTION CHANGE IN THE SOCKET CONNECTION AS SHOWN IN DIAGRAM