I can't hear any sound on the Wireless Concert One.
Your Wireless Concert One may not be turned on, paired, or the volume is too low.
In this case, try turning on your headphones, pairing them again, or increasing the volume.
Also, check to see if the sound is tied to that port. You can connect your headphones to another device using the AUX cable or Bluetooth connection, or connect and check the function.
I can only hear a sound in one ear.
In order to rule out a defect in the headphones, first check in the settings of your end device whether the sound reproduction has been aligned to a certain side. You will often find information about this setting in the operating aids of your devices and in the corresponding operating instructions.