Check the position of the volume control on the device that is attached to the headphones. It may be adjusted as a variable resistor, and with the help of buttons, giving the controller a command to increase or decrease the signal level. Also check you have turned off the sound (Mute) To the computer, start the software mixer (its name depends on OS), and then check the position of the controller, called Master Volume or similar. Also check to see if the flag is off the output socket.
When headphones are plugged into the device not directly but through the active speaker, control volume on both devices. Set them regulators, the coefficients are multiplied by each other: if the zero has at least one of them, the sound will not. Check their position.
Making sure that the regulators are installed in the correct position, but not having the appearance of sound, first check what Jack included earphones. Which to use can be colored green, or nearby, there may be an icon in the form of headphones. If the device has built-in speakers (e.g., laptop, handheld radio), after connecting the plug these speakers must be switched off.
Finding the lack of sound even when properly connected, first check the volume control on the headphones. Slide it from the zero position. If there is no regulator, either it is installed correctly, the absence of sound in one or both channels indicates a fault of headphones, socket or amplifier. If you do not know how to repair them, will entrust this work to a person with the relevant skills. All maintenance operations must be carried out under de-energized equipment.
Some monophonic instruments, for example, analog tape recorders equipped with sockets, connecting to which even good headphones to work is only one channel. To work both, fabricate the adapter, consisting of a stereo plug and socket. The plug connect the two wires to the middle and far contact, and the average does not apply. One of the wires connect to a common Jack contact and the second contacts of the left and right channels connected together.