Split your headphone or line out signal and independently control the volume levels using this Headphone Splitter with Separate Volume Controls.
This simple 3.5mm splitter allows you to distribute a single audio source to two headphones or output devices. This perfect for allowing two people to listen to the same source or to distribute to two different amplifiers. Each line features an independent volume control wheel, so each person can enjoy the audio at the volume level they prefer.
You can also use this splitter as a means of injecting a microphone signal into the source device. For example, you can plug this into your phone and then use a pair of headphones and a separate microphone for hands free communications.
Note that this should NOT be used to combine two audio source signals into a single input. Doing so could exceed signal strength limits and cause damage to your equipment. The only proper way to combine two audio signals is by using an audio mixer.