Hearing Amplification

Hearing loss due to Inner ear pathologies

Hearing aids - History

Professionals who would now be called audiologists became involved with hearing aids in a systematic way in aural rehabilitation centers during World War II.

Hearing Impaired persons of more than a century ago relied on aids such as animal horns and sea shells were used to gather and direct sound waves through the External Auditory Canal allowing them to be amplified.

A listening tube is an example of a device without an external power source.

Cosmetic concerns were very present in the minds of those who used ear trumpets.

There was even an under-the-beard model ear trumpet for gentlemen.

Hearing aids - History

Concepts that are important in hearing Aid use today had already developed:

Amplification of sound energyAmplification of sound energy Efforts to improve signal-to-Efforts to improve signal-to-

noise rationoise ratio Cosmetic concerns regarding Cosmetic concerns regarding

the appearance of the the appearance of the amplifying deviceamplifying device

It was not until the nineteenth century that the first electronic hearing aid was produced.

Popular Styles of Hearing AidsPopular Styles of Hearing Aids

Above: behind-the-ear; in-the-ear; body type hearing aid

Popular Styles of Hearing AidsPopular Styles of Hearing Aids

Above: completely-in-the-canal (CIC); In-the-canal (ITC); in-the-ear (ITE) ; Behind-the-ear (BTE)

models of hearing aids

Main components of Hearing aids Microphone

Converts acoustic energy into electronic signal

Amplifier & Processor Amplifies and manipulates the

electronic signal Receiver (loud speaker)

Converts electronic signal back into acoustic energy

Battery Supply power

Telecoil Telephone use can be difficult for

people with hearing aids. Some hearing aids have a phone

coil.

Telecoil Alternate input source Listens to magnetic signal

instead of (or in addition to) the sound.

Magnetic signal can be from a telephone, CD, TV, personal ALD, headphone, loop

Major advantage is improved signal to noise

Usually on BTEs; sometimes on smaller, seldom on smallest

Magnetic Input Signal

Sound Input Signal

Direct Audio Input (DAI)

Alternate input source Listens to electrical signal

instead of (or in addition to) the sound.

Electrical signal can be from a telephone, CD, TV, or personal ALD

Major advantage is improved signal to noise

Boots available only for BTEs

Booted or Integrated FM

Some Aids have FM receivers either booted on (as shown) or integrated into the aid.

Some can be used with hand-held transmitters or with fixed transmitters which can integrate TV and Telephone.

Clean signal; bridges distance; improves signal to noise ratio.

Especially useful in noisy classrooms with a FM equipped microphone setup for the teacher.

Directional Microphone

Some hearing aids have a switch to activate a directional microphone that responds to sound coming from a specific direction, as occurs in a face-to-face conversation.

One can switch from normal non-directional (omnidirectional) setting, which picks up sound almost equally from any direction, to focus on a sound coming from in front of you.

When the directional microphone is activated, sound coming from behind you is reduced.

Parts of a hearing aid

Types of hearing aid based on type of circuitry Three main types 1) Analog/Conventional

Acoustic signal is converted into one unified but complex electrical current by the microphone.

Analog sound is like making a copy of a photocopy. You get the overall picture but it’s fuzzier and more distorted.

The sound isn’t broken down into its component parts. Limited flexibility Audiologists can make some adjustments This is generally the least expensive type of circuitry.

2) Analog/Programmable

Your audiologist uses a computer to program the hearing aid according to the individuals hearing thresholds.

Allow more than one program which can be controlled by a remote control to accommodate more than one listening environment.

Permits more flexibility than Analog/Adjustable.

3)Digital/Programmable

Acoustic signal is converted into digits zero and ones. Much more precise Details can be changed without effecting the overall

quality. More flexible than analog programmable. In recent

aids, the hearing aid adapts to the listening environment automatically.

Digital circuitry is the most expensive of the above options.

Digital hearing aids use a computer chip and, as a result, offer the most flexibility to your audiologist in making adjustments.

How digital hearing aids work

Digital hearing aid has five major components: The microphone, the analog to digital converter, the

core, the digital to analog converter, and the receiver. Sound waves hit the hearing instrument microphone

where they are converted to an electrical signal (analog).

The signal then passes through an Analog to Digital converter (A/D converter) where it is changed to a sequence of 1s and 0s.

This sequence is sent to the "core" where it is filtered into bands and channels, then manipulated according to the programmed settings for the specific hearing loss.

How digital hearing aids work

This changed signal is then channeled through a Digital to Analog converter (D/A) where the end result is an analog (electrical) signal that has been manipulated according to the hearing loss.

This signal then travels to the receiver where it is converted back to an acoustic signal that the user then hears.

Simply put, the digital hearing aid has a tiny computer chip in it that can manipulate the sound according to specific frequency (pitch) and specific volume level to deliver a clear sound set precisely to the user's hearing loss.

Binaural hearing – Advantages of hearing with two ears Binaural hearing allows you to make fine

judgments about sound and to listen selectively to one of several sounds.

Advantages include – Localized sound Balanced hearing Better speech comprehension Improved sound quality Auditory deprivation

means that further deterioration of hearing, when hearing loss already exists, occurs at a faster rate in an ear without stimulation that it occurs in an ear with stimulation (usage of a hearing aid).

"Use it or lose it."

Cost?

Hearing Aid Type One ear Both Ears

Conventional $700 (ITE or BTE)-1,500(CIC)

$1,400 - $3,000

Programmable $1,100 (ITE or BTE) - $2,000 (CIC)

$2,200 - $4,000

Digital $2,100 (ITE or BTE) - $2,700 (CIC)

$4,200 - $5,400