1pair Rechargeable Semi-In-Ear Hearing Aid Elderly Sound Amplifier 1. Saturation sound level (MAX): less than or equal to 118 +-3dB 2. Output sound pressure level (high-frequency average) 103 +-4dB 3. Full-range sound gain (high-frequency average): 30+-5dB 4. Frequency response range: not narrower than 350Hz-4500Hz 5. Total harmonic distortion: no more than 10 percent 6. Equivalent input noise level: less than or equal to 30dB 7. Powerful noise reduction function, automatic filtering of external noise, so that the sound heard more clearly and truly 8. One-handed contact operation, no need to manually adjust the volume 9. Mirror power digital display, grasp the charging compartment power, goodbye to the anxiety of lack of electricity 10. 120 degrees half into the ear wearing design, stable wearing, not easy to fall off 11. Rechargeable design, long-lasting battery life 12. Intelligent anti-whistling technology, gentle start, to avoid the start of the sharpening screams 13. Size: 23 x 20 x 14.5mm 14. Weight: 3.3g 15. Battery capacity: hearing aid: 40mAh; charging compartment 320mAh