Performance Indicators of Deaf Hearing Aids
A qualified ear machine for deaf should consider at least the following six performance indicators:
1.Frequency range. The frequency range of low-grade deaf hearing aids is at least 300-3000Hz. The frequency range of ordinary deaf hearing aids should be 4000Hz. The frequency range of advanced deaf hearing aids can be between 80-8000Hz.
2.Maximum Sound Output or Saturated Sound Pressure Level (SSPL). In fact, it represents the maximum power output of deaf hearing aids. When using deaf hearing aids, the maximum sound output should be lower than the discomfort threshold of the affected ear. Especially for the re-energized positive ear, the maximum sound output must be controlled to protect the affected ear.
3.Maximum sound gain. It mainly represents the amplification ability of ear machine for deaf. The gain of ear machine for deaf manufactured in many countries is between 30 and 80 dB. Generally speaking, hearing aids with medium or large gain should be selected for those with low degree of deafness and those with high degree of deafness. In the specific use of hearing aids for middle deafness, there are volume control switches which can change the sound gain within a certain range. Selection of suitable hearing aids can be calculated in advance according to some formulas. The simplest method is to compensate and adjust the gain of 500, 1000 and 2000 Hz audio in accordance with pure tone audiogram. It is better to use half or a little more of its threshold to obtain satisfactory results.
4.Frequency response and tone adjustment. In order to meet the hearing requirements of deaf people, ear machine for deaf should provide a variety of different frequency responses, which are different in tone. In order to make the frequency response of deaf hearing aids more in line with deaf people's hearing loss characteristics, tone adjustment buttons are set with some different tones, usually L stands for bass, N is normal, H is high.
5.Signal-to-noise ratio (S/N). The output of deaf hearing aid headphones after amplification is often the coexistence of language signal and annoying noise. The greater the signal-to-noise ratio, the better the quality of language information output. The signal-to-noise ratio of high-quality hearing aids can reach about 40 dB, which should be guaranteed at least over 30 dB.
6.Harmonic distortion. In order to transmit the amplified sound signal at high altitude, the distortion of ear machine for deaf should be as small as possible. According to the regulations, the distortion should be less than 10%, and less than 5% can basically maintain the verisimilitude of the language.