Important Parameters Of The Hearing Aid, You May Not Understand

Hearing Aids Require A Uniform Standard

Hearing aids or acoustic parameters are the main targets of various hearing aid standard specifications and are also required for hearing aid fitting.
Technical parameters that directly affect the wearing effect. From the perspective of fitting, correctly understand and apply the electroacoustics of various hearing aids
It is very important that indicators directly affect the use and function of hearing aids. In real life, many hearing aid fitters often
It is considered that the hearing aid parameters are manufacturers' problems and are the problems of hearing aid quality. They only pay attention to the functions of hearing aids, such as noise reduction.
The number of multi-channel, directionality, etc., are actually not inverted. Generally speaking, the biggest difficulty in learning a hearing aid is to understand this correctly.
The meaning, testing, and application of these technical parameters
There are currently two versions of the assay.
ANSI refers to the American National Standard Specification of Hearing Aid Characteristics
Home hearing aid feature performance standards), published by the American Acoustics Society.
IEC refers to International Electrotechnical Commission (International Electrotechnical Commission) and its "hearing aids"
The standard for performance characteristics test in factory quality inspection
It was originally published in 1959 and has been repaired since then.
Change, its scope has expanded many times, the most recent version is 1983. IEC standards in Europe, the Middle East, and East Asia
Many countries are recognized standards

The main performance indicators of hearing aids are

Saturated sound pressure level,
Full on gain
Frequency response curve,
Equivalent input noise,
Frequency range and distortion, etc.

The Saturated Sound Pressure Level

Saturation sound pressure level (SPL) saturated sound pressure level refers to the specified frequency point, hearing aid
The highest sound pressure level that can be achieved in the plug simulator or coupling cavity. There are usually three ways to describe saturated sound pressure
1) Take the saturated sound pressure level curve
The average of the three points of 1 kHz, 16 kHz, and 2.5 kHz is the average saturated sound pressure level. ANSI 3.22 sets these three frequencies to HA
2) The peak value on the saturated sound pressure level curve can be taken as the maximum saturated sound high voltage level
3) One of three frequencies of 1 kHz, 16 kHz, and 25 kHz can be selected, and the sound pressure level corresponding to the frequency is the saturated sound pressure.
Level, but indicate the test frequency.
Measuring Ssp90 is performed with input 90dB and maximum gain. Under this test condition, almost all hearing aids will
Entering the saturated working state, the measurement of the output sound pressure level (OsPL90) when the input sound pressure level is 90dB is often equivalent to
Measurement of SspL90. But one thing to note is that any amplification system can only provide a limited maximum output, exceeding most
When the input is large, the amplifier can no longer be amplified, and the receiver can no longer convert a larger signal. If the input increases more than the saturation
Horizontal, the output will not increase, but may decrease, the signal will be distorted, so the saturated sound pressure level is not necessarily the highest.
Appears when entering the sound pressure level
Solving the saturated sound pressure level of the hearing aid is essential for the correct selection of the hearing aid, which guarantees: the most
The large output is above the user's threshold. 2 The maximum output produced by the hearing aid does not exceed the user's discomfort threshold

Full On Gain

2. Full on gain: means that at a specified frequency point, the gain is controlled at the maximum (full gear), the other controller is at the specified position, and the hearing aid is measured at the linear input and output. Gain. The circuit is required to be in a state of saturation and compression, and the input-output relationship curve is substantially linear. When measuring, the volume potentiometer is in full position, input a medium-intensity sound (50DB or 60DB), sweep in the range of 200-8000HZ, and measure the frequency response curve of the full-scale gain. If the 60DB SPL input sound has saturated the hearing aid output, consider using a 50DB SPL input sound. For hearing aids that cannot manually turn off the AGC function, the 50DB SPL input sound is also used to prevent the AGC circuit from starting. When the full-range sound gain is described as a numerical value, two values are usually taken, one is the peak full-range sound gain value and the other is the average full-range sound gain value of the high-frequency average HFA (1000hz/1600hz/2500hz). Usually, the IEC standard takes the peak value, and the ANSI value is the HFA is the full-range sound gain.
The practical significance of the full-range sound gain indicator is used to indicate the maximum amplification capability of the hearing aid.

Frequency Response Curve

3 The frequency response characteristic 2: Basic frequency response curve When the input sound pressure level is 60 dB SPL, the frequency response curve measured at the reference test gain control position
The curve of the change in the output gain of the hearing aid as a function of the frequency of the input signal is called the frequency response curve. This upper-frequency response curve is not based on the maximum gain. If you change the ordinate of the output (as shown in Figure 95 for the deaf and hearing aids) to the output sound pressure level, the resulting curve is the frequency response curve (see Figure 96). The hearing range of the human ear is 20-20000 Hz, and the language frequency range is 500-2000 Hz. Experiments prove that the low frequency mainly provides the energy of the language, while the high-frequency hearing compensation is of great significance to the clarity of the language, so the frequency of the hearing aid from 250-4000 Hz The gain value of the curve is important for the selection of hearing aids.

Equivalent Input Noise

4 equivalent input noise: it is an indicator to evaluate the inherent intrinsic noise of hearing aids. When testing, the internal noise can be approximated, etc.
Change to input noise, the specific test method is: open the hearing aid and turn off the sound source and measure the noise level of the output noise (dB)
Value), minus the reference test gain (dB value) of the hearing aid, that is, the equivalent input noise level is obtained.

Frequency Range And Distortion, Etc.

5 The distortion of the hearing aid When the signal transmitted by the hearing aid is different from the characteristic of the original input signal, it becomes distortion and is called distortion.
change. Hearing aid distortion includes harmonic distortion and intermodulation distortion. When the output signal produces a signal that is an integer multiple of the original frequency, it is called
Wave distortion. For example, the frequency of the original input signal is 1, and the output signal contains 2 kHz, 3 kHz in addition to 1 kHz.
The frequency components such as z are called harmonic distortion components. The original input and output signals are 1kz, called the fundamental or fundamental.
The 々kH in the output signal is called the second harmonic, and the 3 kHz is called the third harmonic. The ratio of the output of each harmonic quantity to the fundamental output,
The percentage of harmonics is obtained; the sum of each chopping is called total harmonic distortion. We want the distortion to be as small as possible, but it doesn't happen at all.
Wave distortion is unrealistic, with less than 3% distortion, which is not easily recognized by human ears. Because usually less than 3% is used as a harmonic
Real factory indicator requirements
Intermodulation distortion refers to when the input signal is two signals of equal amplitude, such as 0 kHz and 1 kHz, the two signals pass through.
After the hearing aids, in addition to their respective harmonics 16kHz, 24kHz, 3.2kHz and kHz, 3kHz, 4kHz
The sum and difference of the frequencies of the two input signals appear, that is, the components of 08 kHz +1 kHz = 1.8 kHz and 1 kHz 0.8 kHz = 0.2 kHz.
The distortion is called intermodulation distortion. When the hearing aid receives complex frequency components such as language and music, if the line of the hearing aid itself
Poor sexual characteristics, often cause intermodulation distortion
The above is the basic indicator parameter of a hearing aid.


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