Implementation of Open Ear Option

Implementation of Open Ear Option

1. Selection of vents
The primary design goal of the open ear option is to help the sound and pressure in the external ear canal find a suitable flow path, reduce blockage, increase air flow, balance internal and external air pressure, and enhance the listening comfort of the wearer. The most direct and effective tool to alleviate the ear plugging effect in science. The theory shows that the amount of change in the low-frequency enhancement caused by bone conduction by the vent hole depends on the acoustic mass and is inversely proportional to it. At the same time, the acoustic torque is proportional to the length of the vent hole and The pore size is inversely proportional. Kuk mentioned in the report that the ear plugging effect of traditional ear molds with full cavity is about 20dB.
For every 1mm increase in the inner diameter of the hole, the plugging effect can be alleviated by about 4dB. Therefore, this also means that if you want to completely eliminate the ear plugging effect, the inner diameter of the ventilation 7L must reach about 5mm, but without the support and assistance of any digital technology, simply making a vent of this size in the traditional full-ear shell cavity Ear molds and custom hearing aid housings are difficult to achieve.
Now widely used in the open ear optional vent hole types and earplug types include: step vents (flex vent earmolds), open dome (open dome), enhanced earplugs (power dome) and tulip dome. Among them, the research and development organization of the stepped vent hole thinks that the stepped vent hole can reduce the blocking feeling by 30%, and at the same time change the formant of the frequency response curve, shifting the formant that may generate feedback outside the frequency response range of the hearing aid .
2. Digital signal processing
(l) Feedback control
Although the increase of the inner diameter of the vent hole can effectively alleviate the occurrence of the ear plugging effect, while the inner diameter of the vent hole increases, the residual resonance effect of the ear canal also promotes the high-frequency gain of the hearing aid at 2.0 to 3. OkHz, Increasing the incidence of feedback, affecting the frequency response curve of hearing aids, and limiting the scope of hearing aids. Therefore, it is not easy to really achieve the ideal open ear matching effect simply by expanding the inner diameter of the vent hole. The first challenge that needs to be met is the suppression of feedback.
Currently, inverse phase processing technology is the most advanced feedback suppression technology in the field of hearing aids. This technology means that when the hearing aid microphone detects a feedback signal existing in space, it will automatically generate a phase wave with the same magnitude and opposite polarity as the feedback signal to superimpose, thereby accurately and effectively canceling the original feedback signal to ensure that The probability of howling of the hearing aid is reduced to a minimum, which ensures that the theoretical gain of the hearing aid can be effectively applied, and provides a headroom gain of 10 to 20 dB for the hearing aid.
(2) Operation rate
The presence of Ventilation 7L not only threatens the incidence of hearing aid feedback. In fact, more ambient sound signals will also easily enter and exit the larger-aperture vent holes used in the open ear option, and reach the tympanic membrane directly, forming An independent sound conduction and resonance system. Therefore, as long as the difference in the rate of calculation of the sound signal between the open ear hearing aid and the natural transmission speed of the sound can be detected by the human hearing system, the time when the same sound signal reaches the eardrum will be different, and human hearing The system’s judgment and approval of this sound signal may also differ. For example, when the sound signal transmitted directly through the vent is 20dB lower than the signal output strength of the hearing aid, and at the same time is lower than the hearing threshold level of the hearing aid wearer, the signal passed directly will be masked or ignored due to the low intensity (quiet Or soft voice environment). However, once the intensity of the sound signal directly transmitted to the person is close to the signal output strength processed by the hearing aid, or when it is higher than the hearing threshold level of the hearing aid wearer, the hearing aid wearer is likely to be in front of and behind the same time axis. Hear two sounds with the same content, or the phase of the two sound signals is canceled or enhanced. In addition, if the sound signal directly transmitted is higher than the signal output intensity processed by the hearing aid, that is, in a high-noise environment, when the hearing aid suppresses noise, the directional noise reduction function or other noise reduction technology in the open ear option is opened. The original effect will be lost, and the actual signal-to-noise ratio will also have a certain gap with the theoretical value. Therefore, as far as the open ear option is concerned, the arithmetic compression speed of the hearing aid chip also has quite high technical requirements.

With the development of modern new hearing aid digital chip technology, the processing speed of digital signals has also achieved a qualitative leap. At present, the hearing aid chip not only can better meet the requirements of the sound processing speed of the open ear selection pairing, and avoid improper delay of signal processing. At the same time, its advanced compression system can also automatically adjust the frequency division point, which effectively improves the gain compensation. Accuracy reduces the appearance of distorted signals.
3.3.3 Earphone technology
1. Defects of traditional open ear matching
In traditional open ear matching, especially in the ear canal hearing aid, even if it is combined with the latest modern open digital signal processing technology, it can solve the problem of ear plugging effect in a certain sense, but Due to the existence of large-aperture vents, there are still some shortcomings in the process of the open-ear hearing aids in processing signals, which still cannot meet the needs of all wearers. Among them, the low-frequency gain dip and insufficient overall gain are the two most important problems.
(l) Low frequency gain decline
When the inner diameter of the vent hole is increased, the output intensity of the conventional open-ear hearing aids at frequencies below 1.0 kHz will decline to a large extent. As shown in Figure 3-7, compare the hearing aid output curve of a full-ear cavity cavity ear mold with the output curve of a hearing aid with a 3 mm inner diameter vent hole ear mold. At 25kHz, the difference is -20dB, and for open-ear hearing aids with large-aperture air holes, even at 1. At okHz, there is also a -10dB difference between the output of the hearing aid and the hearing aid of the full-ear cavity cavity ear mold. Therefore, if the low-frequency hearing of hearing-impaired people who need optional hearing aids should be compensated, the traditional open-ear hearing aids cannot meet his needs.
Frequency [Hz]

Hearing aid output with different inner diameter vent hole ear molds

(2) Insufficient overall gain
. Psychological research shows that people always have desires and pursuits for beauty, so ear canal hearing aids are also praised by hearing-impaired people because of their special concealment. However, due to the limitation of the volume, the distance between the microphone and the receiver of the ear canal hearing aid is often small, and coupled with the large-aperture vent, the risk of feedback from the ear canal hearing aid is particularly prominent. Therefore, the theoretical gain of the ear canal type open ear hearing aid cannot be truly realized, and the gain required by the wearer of the ear canal type open ear hearing aid cannot be satisfied.

2. Birth of the earphone technology (RIC / RITE)
It is precisely because of the above-mentioned problems that the power of open-ear hearing aids is often slightly insufficient, and open-ear hearing aids are selected. It can only be used for hearing-impaired people whose low-frequency hearing is close to normal and high-frequency has mild hearing loss. Therefore, in order to better meet the hearing loss needs of different types of hearing loss and various types of hearing impaired, audiologists meet the psychological desire for hearing aids to be compact, lightweight, and concealed, comfortable and beautiful, in addition to digital processing technology. In addition to the adjustment of open ear options in the field, considerable adjustments and tragic changes have also been made in hardware, such as the emergence of invisible open ear sound tubes and open earplugs, miniaturization of hearing aid components, and the latest ear canal style. receiver.

The research and development of earphones has opened the distance between the earphones and the earphones of traditional earphones, which not only effectively reduces the probability of feedback, but also increases the headroom gain when the earphones are equipped with optional earphones. It is placed outside the ear canal and leaves the body of the hearing aid. Therefore, the receiver will be closer to the eardrum, and the output gain and adaptation range of the hearing aid will be increased. More importantly, the external of the receiver saves the body of the hearing aid. Space, without the help of miniaturization of components, the volume of the hearing aid body is greatly reduced, becoming more beautiful and concealed. In addition, you only need to replace the original open earplugs or open ear molds with the earphone housing of the built-in receiver, which can meet the needs of people with severe hearing loss who can only choose high-power, large-volume earphones.
3． Structure of ear canal receiver
The front end of the ear canal type receiver is connected to the open ear plug by plugging and unplugging, and the rear end is connected to the hearing aid body through a receiver fixing device, a metal wire, a transparent insulation tube with an inner diameter of 0.8 mm, and a metal interface. , Only need to use the ear canal shell with the fixing device to replace the original receiver fixing device,
Figure 3-8.
Earphones are currently divided into three basic length and curvature specifications according to the size of the ear. The metal interface with the body is currently divided into ring sockets (rotary locks) and probe sockets. Convenient, and the invisible transparent insulating tube is like a shrink tube, which tightly wraps the metal wire of the receiver and the fuselage.
In addition, it should be noted that the metal wire and the transparent insulating tube are relatively easy to wear and need to be replaced regularly, and such replacement needs to be replaced together with the receiver, because the receiver and the metal wire are completely fixed.
3.3.4 Open ear optional standard
Figure 3-8 Structure of the ear canal receiver
The current open ear technology can almost meet the requirements of comfortable wearing and concealed appearance. Therefore, when audiology clinicians choose open ear hearing aids for people with different types and degrees of hearing impairment, they only need to pay attention to which earplugs or ear molds are selected to meet their needs for hearing aid output power and the optimal adjustment of parameters. Generally speaking, a ventilation hole with an inner diameter of 0.5 to 1.0 mm is suitable for people who have a hearing loss of 50 to 60 dB at 0.5 kHz, and a ventilation hole with an inner diameter of 0.5 to 1.0 is suitable for a hearing loss of 40 to 49 dB at 0.5 kHz. People, 2. O ～ 3. Omm inner diameter vents are suitable for people with hearing loss of 30 ～ 39dB at 0.5kHz, 3. O ～ 4. Omm inner diameter ventilation holes are suitable for people who have 20 ～ 29dB hearing loss at 0.5kHz. 4. Omm inner diameter ventilation holes are suitable for o. People with a hearing loss of <20dB at 5kHz.
In summary, the open ear option has met the needs of hearing aids with different hearing loss levels and types through the continuous innovation of sound transmission systems and digital signal processing systems. They can more clearly and naturally feel their own voices with the outside world. Nai also increasingly replaces traditional ear canal hearing aids due to its exquisite and concealed appearance. Therefore, as a new member of the hearing aid family, audiology researchers believe that more hearing-impaired people will definitely enjoy the more practical help brought by the open ear matching.