Deafness: A general term for varying degrees of hearing impairment caused by organic or functional lesions in the auditory conduction pathway. Hard of Hearing: A lesser degree of deafness. Deafness: Hearing loss that significantly affects the ability to hear to a normal degree. Classification of deafness: Conductive deafness: Hearing impairment due to lesions of the acoustic conduction pathways, i.e., the outer and middle ears. Sensorineural deafness: Hearing impairment due to lesions of the perceptive and analytical pathways of sound waves, i.e., the auditory nerve and auditory center of the inner ear. Mixed deafness: Both. Classification of deafness: Humans can hear sounds in the frequency range of 20 – 20,000 Hz. The frequency range of speech in general is mainly 500 – 3,000 Hz. The average hearing threshold of 500Hz, 1000Hz and 2000Hz is used for clinical grading: 1. Mild hearing loss: the pure tone hearing threshold is 16 – 25dBHL. 2. Mild hearing loss: the average hearing threshold is 26 – 40dBHL for inaudible whispered speech at a normal distance. 3. Moderate hearing loss: the average hearing threshold is 41 – 55dBHL for difficulty in listening to normal conversation. 41—55dBHL. 4.Moderate to severe hearing loss: hearing loud also feel difficult, the average hearing threshold is 56–79dBHL. 5.Severe hearing loss: can only hear loud shouting in the ear, the average hearing threshold is 71–90dBHL. 6.Extreme hearing loss: can hardly hear any sound, even loud shouting in the ear can not be heard, the average hearing threshold is above 90dBHL. The average hearing threshold is above 90dBHL. Prevention and treatment: 1.Sensory nerve deafness: optional hearing aid technology, electronic cochlear technology. 2.Conduction nerve deafness: various types of improvement and hearing surgery. 3.Mixed deafness