Convenient wearLow noise， low distortion;For people with severe hearing loss;Product use hearing assistive devices.The scope of application of gas conduction hearing disorders.Taboos otitis media or ear suppuration who are disabled.Features:Maximum sound output: 130 �� 5dB Sound gain: �� 50dB Total harmonic distortion: �� 5% Frequency range: 300Hz ~ 40000Hz Input Noise: �� 30 dB Operating voltage: 1.5V Battery model LR44 Current: �� 4mAWeight: 74gInstructions�� The wire plug connected to the headset.Then earplug connector (hard) to the headset， earbuds (silica gel) to connect to the headphone connector pedestal The battery installation: Gently open the battery compartment cover， put a AG13/LR44 battery into the battery compartment in the right direction， then close the battery compartment .Before you use this item ，you have to turn the O-N switch to O(off)，and turn the sound volume to minimumThen put this item on you ear， keep it tightlyNext， turn this item on(O-N to N)， adjust the volume until you hear clear sound