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Page: Hearing Aid Technology
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Wireless
Recent hearing aids include wireless hearing aids. One hearing aid can transmit to the other side so that pressing one aid's program button simultaneously changes the other aid and both aids change background settings simultaneously. FM listening systems are now emerging with wireless receivers integrated with the use of hearing aids. A separate wireless microphone can be given to a partner to wear in a restaurant, in the car or in another room. The voice is transmitted wirelessly to the hearing aids reducing the effects of distance and background noise.
Many theatres and lecture halls are now equipped with assistive listening systems that transmit the sound directly from the stage; audience members can borrow suitable receivers and hear the program without background noise
Directional microphones
Directional microphones are currently the best way to improve the signal to noise ratio, and thus, improve speech clarity in noise for the wearer.
Many hearing aids now have directional microphones, which can be a major improvement in crowded places such as restaurants and open-plan offices, because the directional microphone allows the user to focus on whoever is directly in front with reduced interference from conversations behind and to the sides. It is common for such a hearing aid to have both a directional microphone and an omnidirectional microphone and a switch that lets the user choose between hearing in all directions versus hearing only in the direction his or her head is facing. Some more-advanced models can electronically subtract signals so the user hears the directional signal minus the omnidirectional signal for improved background noise rejection.
Adaptive directional microphones are a further sophistication of the concept. The hearing aid processor is able to distinguish noise as opposed to speech and automatically reduce the particular noise source from a certain angle. The limitations are at the identification level, where a noise that behaves similarly to a speech signal is difficult to identify, thus reducing efficacy. In severe background noise, the directional microphone is less efficient, however benefits may still exist.
The recently introduced eyeglass aid by the Dutch company Varibel uses four microphones on each side of the frame of a pair of glasses that, together, work as two directional microphones. Technology inside the frame is able to discern between sounds coming from the front and sounds coming from the sides or back, amplifying the sound which is coming from the direction in which the user looks, suppressing other sounds. It should be noted that these hearing aid glasses are not used by most hearing professionals due to their vulnerability to damage and the difficulty that occurs when repairs have to be made. It is very hard to find local (in the US) manufacturers that still have the tools/pieces needed for any repairs.
Telecoil
Telecoils (T-coils) allow different sound sources to be directly connected to the hearing aid, improving sound quality and allowing the hearing aid wearer to easily perceive the intended signal regardless of background noise. They can be used with telephones, FM systems, induction loop systems and public address systems. Such hearing loop systems are widely used in public places such as churches, shops and railway stations in the UK and some Scandinavian countries.
T-coils are comprised of a metal core (or rod) around which ultra-fine wire is coiled. T-coils are also called induction coils because when the coil is placed in an electromagnetic (EM) field, an alternating electrical current is induced in the wire (Ross, 2002b; Ross, 2004). The T-coil detects EM energy and transduces (or converts) it to electrical energy. T-coils can also be used to pick up magnetic signals, just as a microphone picks up an acoustic signal; the T-coil then sends the signal to the hearing aid circuit or processor for amplification.
A problem with T-coils is that they pickup lot of buzz too. In many places there are many sources of electromagnetic fields, such as computers, electric cables, cellphones etc.
DAI
Direct Audio Input (DAI) allows the hearing aid to be connected to an external audio source like a CD player or an assistive listening device (ALD). This is preferred by many users, as opposed to using a T-coil with a standard set of headphones, as there is less interference (usually heard as a buzzing noise).
Processing
The inside mechanisms of hearing aids vary among devices, even if they are the same style. Three types of circuitry, or electronics, are used:
* Analog/Adjustable: The hearing professional (Audiometrist, Hearing Instrument Specialist, Hearing Aid Dispenser, or Audiologist) determines the volume and other specifications required for the patient's hearing aid, and then a laboratory builds the aid to meet those specifications. The hearing professional retains some flexibility to make adjustments. This type of circuitry is generally the least expensive and also the least effective.Many manufacturers have actually discontinued their analog devices.
* Analog/Programmable: The hearing professional uses a computer to program the hearing aid. The circuitry of analog/programmable hearing aids will accommodate more than one program or setting. If the aid is equipped with a remote control device, the wearer can change the program to accommodate a given listening environment. Analog/programmable circuitry can be used in all types of hearing aids.
* Digital/Programmable: The hearing professional programs the hearing aid with a computer and can adjust the sound quality and response time on an individual basis. Digital hearing aids use a microphone, receiver, battery, and computer chip. Digital circuitry provides the most flexibility for the hearing professional to make adjustments for the hearing aid. Digital circuitry can be used in all types of hearing aids and is typically the most expensive. However, digital hearing aids can be specially programmed with multiple programs for quiet situations, background noise reduction, music listening, and directionality. Many also have more powerful feedback-reduction and/or cancellation technology. Among digital hearing instruments, some companies are providing hardwired configurable platform, while others are providing software programable platform based on the utilization of a programable low power DSP.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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