Forum Proceedings

Technology Area

Researchers, manufacturers and end‑users identified earmold materials, fitting and production as technology areas that could benefit from technological innovation and refinement. They believed that development of improved earmold technology would meet important user needs and represent significant business opportunities.

[ Top of Page ]

Market Need

It is estimated that more than 20 million people in the United States experience some form of hearing loss. Yet, according to research reported by Dr. Sergei Kochkin, only 21% to 22% of the people use hearing devices (Kochkin, 1997b). Further research indicates the reasons that people who experience hearing loss chose not to use the available technology include: hearing aids do not perform in noisy situations (7.1 million), provide too much whistle or feedback (6.4 million), do not work well (4.8 million), work only in limited situations (4.3 million), have poor sound quality (3.9 million), break down too much (3.4 million), cannot be used on the telephone (3.1 million), and negative experiences of friends (3.9 million) (Kochkin, 1997a).

As previously mentioned, a common annoyance is the presence of feedback (6.4 million) experienced by the hearing aid user. There are two types of acoustic feedback: (1) produced internally from the hearing aid, indicating a need for repair; and (2) the more common cause, externally produced feedback due to leakage of amplified sound, that radiates from the speaker and then is picked up by the microphone and re-amplified. In many cases, the feedback can be addressed by either repositioning the hearing aid or by reshaping the earmold so that its fit conforms more closely to the shape of the ear canal (Smedley & Schow, 1998; Sweetow, 1998).

The earmold provides several basic functions. First, it couples the hearing aid with the user's ear. It channels the sound from the hearing aid, through the ear canal, to the eardrum. The earmold also helps to secure the hearing aid in place. The challenge is to provide the user with a secure fit. Yet the tighter the fit, the more uncomfortable the device is to wear. A well‑fitted earmold directs sound from the hearing aid to the ear without feedback, thus allowing the user to hear comfortably (Lachapelle, 1999). Earmolds are required for all hearing aids, and since the anatomical structure of the ear varies from person to person, the majority (80%) of all earmolds are custom‑made.

An earmold is also used to protect hearing in environments with loud noise. For example, the earmold can be used in recreational settings such as car racing, hunting, and for fans of sports or music during games and concerts. It also provides hearing protection for industrial workers such as carpenters, factory workers, machinists, and others (Earmold Design, 2000).

The use of earmolds for Assistive Listening Devices (ALD) is less common; however, in those situations where earmolds are appropriate, the general characteristics do not vary from those of a hearing aid. Only 5% of the people who experience hearing loss use ALDs (National Center for Health Statistics, 1997).

[ Top of Page ]

Basis for Discussion

There is a need to improve the comfort of earmolds while maintaining the secure fit necessary for proper hearing aid function, including the reduction of acoustic feedback.

Chewing, yawning, and other facial movements change the geometry of the ear canal structure. As the anatomic structure changes, the fit of the earmold is affected causing an increase in acoustic feedback. The hearing instrument may dislodge from the ear if the ear canal's shape is changed.

Feedback occurs when the hearing aid does not fit properly and the output signal leaks around the earmold, is received by the hearing aid microphone, and is amplified. Other causes of feedback include the vents that are drilled into them. Vents are used to reduce the "plugged up" feeling experienced when the user speaks. However, the vent also provides an opening for the sound to create feedback within the hearing aid. At high amplification the output signal can again be picked up by the hearing aid microphone and be amplified. Users who experience significant feedback will adjust the hearing instrument's gain, or will turn it off completely. In the worst case situation, the hearing aid user will stop wearing the device all together.

Issues that relate to hearing aids are equivalent to the issues for earmolds used for hearing protection. The overall fit and comfort are critical in the success of providing protection to the hearing of the user in environments with sustained high noise levels.

[ Top of Page ]

Statement of the Problem

The earmold is an important link in fitting a hearing aid system and must meet multiple requirements. The earmold must:

• Provide a satisfactory acoustic seal.
• Acoustically couple the hearing aid to the ear.
• Retain the hearing aid on the pinna (auricle).
• The earmold must be better integrated into the overall design and performance of the hearing aid.
• Be comfortable to wear for an extended period.
• Be aesthetically acceptable to the user.
• Be of a style that the user can physically handle.

Failure to meet any of these requirements will increase the likelihood of product abandonment by the user. Therefore, Stakeholders desire improvements in the fitting, production, comfort and performance of earmolds as they are used for hearing aids or as hearing protection devices.

[ Top of Page ]

Current Technology

Custom modification of the earmold aids in the overall fit (comfort & security) and minimizes acoustic feedback. These custom designs are handmade which is time consuming and costly. Yet, the time taken to properly fit the ear canal in the beginning may reduce the need for modification to the earmold shell later.

There are a number of options in the type of materials used to create the earmold. Proper selection of the material is critical to improve the overall fit and comfort to the user. Some materials may cause allergic reactions for the user, some provide options in colors, while others are simply more comfortable for the user (individual perception). Material characteristics or properties may change over time and become hard, or may experience shrinkage causing poor fit or discomfort to the user. hearing aid. Three of the most common options include; venting, dampers and horn effects. Each will affect different portions of the hearing aid response curve (Microsonic, 2000a).

Venting is an opening that is drilled into the earmold to release low frequency sound. This reduces the "plugged feeling" experienced by the hearing aid user while speaking, described as "talking inside a barrel." This sensation is called the occlusion effect.

Dampers are materials that are used to alter the frequency and decrease unwanted peaks of sound waves. Common materials used include wool, plastic and metal, which fit inside the earmold tubing.

The horn effect is provided when the bore of the earmold increases as it goes deeper into the ear canal. It increases and extends the high frequency sound waves. A reverse horn effect is achieved by adapting the earmold to gradually narrow towards the inner portion of the ear canal.

Additional adjustments to the earmold can be made by buffing and shaping the product for a better fit. However, this is a "hit and miss" approach. Another method of securing the earmold in the ear canal is to wrap the shell with a flexible material that will provide a temporary solution to the problem.

Health care professionals must evaluate each person individually as to the material and style selection of earmolds to best meet their needs and to ensure the highest success rate with the hearing aid. Issues to consider include:

• whether the user is active or sedentary in their lifestyle,
• user dexterity (for example, the persons ability to handle hearing aid insertion, daily care, and cleaning of the earmold),
• the anatomy of the individual's ear and the affect it has on the choice of material or style of hearing aids that are to be used (anatomic considerations when choosing a hearing aid include: a deformed outer ear, the depth of the concha, whether ear canal is of sufficient diameter and whether there is a sharp enough bend to hold the hearing aid),
• growth changes, (in particular children),
• changes in morphology of the ear canal as it slowly adapts to the continuous pressure of the device (continuous pressure may cause the area to expand slightly),
• amplification objectives of the fitting,
• toxicity or allergies to plastics,
• appearance -- color selection, hearing aid style and earmold design options, and
• the number of modifications that ma be required after delivery of the device (Microsonic, 2000b).

Each manufacturer offers a variety of materials to be used with earmolds to meet the specific needs of each client. Choosing the correct material for earmolds is as important as determining the earmold style and acoustics. Some of the generic varieties include:

• Acrylic is used to create hard custom earmolds, used with mild to severe hearing losses. Most earmold styles can be made with acrylic and are available in a range of color options.
• Polyethylene is a semi-rigid material and is hypoallergenic. It is used for mild to severe hearing losses. Polyethylene is not as durable as other materials and should be handled with care. The color selection is limited to white.
• Silicone is a flexible inert material that is useful when fitting client's with allergy problems (although the hypoallergenic feature is not available if produced in any color other than beige or clear). There is little to no shrinkage with silicone and can therefore be used when fitting high‑power hearing aids.
• Lucite is a clear synthetic plastic resin that is rigid at all temperatures. It is useful for mild to moderate hearing losses. It does not shrink over time, is easy to grind and buff, but is not recommended for children.
• Poly Vinyls (Polymerized vinyl) provide a soft, comfortable fit with a superior acoustic seal. The texture of the material provides a rich mellow sound quality that preserves the harmonic and resonant characteristics of the ear canal.

[ Top of Page ]

Issues to Consider

• Are new materials available to provide the comfort and snug fit needed to produce the highest level of speech recognition while reducing acoustic feedback?
• What methods of making an impression of the ear canal could be improved to create a better earmold?
• Is there a better way to measure the internal cavity of the ear canal that could be transmitted to a computer program that fabricates the earmold?
• What type of adjustments should be available to the earmold once a client has been fitted with the hearing aid?
• What physical characteristics in the materials used for making earmolds would enhance the ability to make alterations once the mold has been created?

[ Top of Page ]

References

Earmold Design. (2000). Hearing & Ear Protection - Introduction. Available: www.earmolddesign.com/catalog_html/36.htm [April 10, 2000.

Kochkin, S. (1997a). Customer Satisfaction & Subjective Benefit with High Performance Hearing Aids. Knowles Electronics. Available: www.knowlesinc.com [April 19, 2000].

Kochkin, S. (1997b). MarkeTrak IV: What is the Viable Market for Hearing Aids? Knowles Electronics. Available: www.knowlesinc.com/ [April 20, 2000].

Lachapelle, R. (1999). The Earmold. Available: www.rayshearing.com/earmold.htm [April 10, 2000].

Microsonic, Inc. (2000a). Custom Earmolds -- Acoustic Options. Available: www.earmolds.com/acoustic_opt.htm [April 10, 2000].

Microsonic, Inc. (2000b). Patient Evaluation for Earmold Selection. Available: www.earmolds.com/patient_eval.htm [April 10, 2000].

National Center for Health Statistics. (1997). Advance Data (292). Washington, DC: Vital

Statistics of the Centers for Disease Control and Prevention.

Smedley, T, & Schow, R. (1998). Problem-Solving and Extending the Life of Your Hearing Aids. In R Carmen (Ed.), The Consumer Handbook on Hearing Loss and Hearing Aids - A Bridge to Healing (pp. 130-158). Sedona: Auricle Ink Publishers.

Sweetow, R. (1998). Hearing Aid Technology. In R Carmen (Ed.), A Consumer Handbook on Hearing Loss & Hearing Aids - A Bridge to Healing (pp. 111-129). Sedona: Auricle Ink Publishers.

[ Top of Page ]