Ear Moulds

1. Definition:

An ear mold is the individually fabricated ear insert that channels the sound reproduced by a hearing aid through the ear canal to the ear drum. In most fittings & configurations, the earmold must:

Ø To provide a satisfactory acoustic seal.

Ø To couple the hearing aid to the ear acoustically.

Ø To retain the hearing aid on the pinna.

Ø To modify acoustically the signal produced by the hearing aid.

Ø To be comfortable to wear for an extended period of time & non allergic.

Ø  To be aesthetically & cosmetically acceptable to the client.

 (Mynders, 1996)

To meet these requirements, the ear mould must be crafted skillfully from an ear impression that properly reflects the anatomical structures of patient’s ear.  Certain structures of the earmold are designed to perform one or more functions. These functions include providing

---sufficient acoustic seal

--- adequate in-air retention

---necessary comfort

--- proper sound direction

---ease of insertion.

v Acoustic seal

                         The acoustic seal occurs between the ear canal aperture & the canal second bend. It needs to be comfortably snug & accurate, if not it may lead to acoustic feedback which occurs due to amplified signal escaping from the ear canal, reaching the microphone, & causing the amplifier to oscillate.

v Earmold retention

                             The efficiency of earmold retention depends on natural prominences and present in the concha and canal. Retention is provided by a bulge in the earmold. . When the earmold is fitted,the bulge holds it securely in the canal. Retention for full concha earmold occurs at the area of the helix,tragus and anti-tragus. Retention for canal molds is found in the ear canal.

v Earmold comfort

                              To be comfortable, an earmold should fit snugly in the canal cartilaginous tissue and make no contact with the bony portion of the ear. The snug fit is defined by several factors including impression taking technique and material, and in lab impression trimming and coating.

v Earmold sound direction

                               The sound bore on the earmold should be directed towards the eardrum. This can be achieved easily in ears that have straight or crooked canals. In ears that have sharp bends, the sound direction may be compromised to some extent with the earmold ‘s insertion.

v Earmold insertion

                        Earmold insertion is defined in the manufacturing process through skillful trimming of the helix and canal portion of the impression.  An earmold that cannot be easily inserted is most likely made from an inadequately trimmed ear expression.

                               

   ii.        Parts of an earmold:

The human external ear consists of the pinna, ear canal, & eardrum. The canal has two bends, with the eardrum located beyond the second bend. Anatomically, the section between the ear’s first & second bend is made up of moderatively sensitive cartilaginous tissue. This tissue is soft & often lined with earwax produced by wax glands situated deeper in the canal. Fortunately for earmold fittings, the cartilaginous portion can be stretched by the earmold body & still remain within comfort limits. The ear canal cartilaginous tissue also is subject to shifting resulting from jaw movements. The jaw’s downward movement commonly stretches the anterior (front) ear wall & increases the ear canal diameter.

Beyond the canal’s second anatomical bend, the cartilaginous thins & eventually disappears, & the earwall becomes more rigid. The underlying tissue of the ear canal bony section, which is quite thin, has no subcutaneous layer, is highly vascular, & is quite sensitive(staab, 1994). An earmold that presses against the canal body tissue creates enough pressure to make the mold difficult to tolerate. Although this tolerance to pressure varies among individuals, the feeling of discomfort is common. Hence the parts of the molds & shells can be described by the corresponding parts of the ear in which they fit. ( earmolds & shells of different styles fill different portions of the concha & the canal).  

Earmold materials

                              There are different types of materials used in the manufacturing of earmolds.    

	Lucite: Hard Clear Acrylic                                              This material is an excellent all-purpose ear mold material. It is durable, very seldom discolors and allows the greatest versatility for modification. This is available in crystal clear, or tinted in a variety of colors.
	Dermatex: Vinyl Solid Flesh                                         Dermatex retains flexibility regardless of temperature changes. It provides an added degree of comfort and safety and is ideal for tender sensitive ears. Dermatex material is extremely rugged and durable, flexible and specially recommended for children as a safety measure against injury. Dermatex is available in flesh and brown tint.
	Protex: Vinyl                                            Protex has all the qualities of the dermatex, but in addition is a little softer and has the quality of obtaining a very tight seal for your severe losses. Protex is available in clear and tinted pink and brown. It can also be tinted in a variety of primary colors.
	Polyethylene: Non-Toxic Hard Plastic                                        Adverse skin reaction to most earmold materials is very rare. When such an allergy is suspected or takes place, the individual should be referred to a physician for confirmation. Earmold concepts non allergenic, non toxic, polyethylene earmold material is available in most styles of earmolds, and is available in opaque white
	Silicone: Solid Flesh Non Allergenic                                          Silicone molds are made from a medical grade elastomer, the most ideal material for a perfect seal for your problem ear level cases and the ideal solution for your high powered ear level aids that cause feedback. It’s available in flesh and opaque clear and brown and pink.
	Softex: Soft Acrylic  This material is a semi-rigid material. Soften to the body temperature. And is available in clear and pink and brown.
	Medi-Cryl: Hard Flesh This is an acrylic flesh colored material, it is the same material used to manufacture the ITE and the CIC hearing aid shell.
	Hardbody/Softtip: This material is a hard clear Lucite body with a soft tip canal. Allowing comfort and seal at the same time. This material comes in clear or tinted pink or brown.

Types/ styles of Ear molds:

                                                        One of the difficulties in describing different styles of earmolds is the lack of standardization of names. Although NAEL agreed on some standard names in 1976, many new styles have been invented & re-invented since then. Some ear molds are given a descriptive name (e.g. Skeleton), some are named after an inventor (e.g. Janssen) & some are confusingly named after the application in which they were originally used (e.g. CROS)

There are a no of earmolds available from different earmold manufacturers & they vary from each other.:

 

Occluding                                 open fit    

               

                   Non-occluding

OpenFit

                                 This has become the newest style of ear mold. The most discreet and open. The whole design reduces the occlusion effect. The tip is made up of very soft material and it keeps the ear ventilated. It enables low frequency sounds to flow in and out of the ear without being amolified. The open fit is originally designed for patients with minor and moderate loss in the higher frequencies.

Occluding moulds:

Occluding molds are those that have no intentional air path between the inner part of the ear canal & the outside air.

Standard:                        This is also known as a "Receiver" mold and is used with snap-in receivers for body aids and where extreme feedback is a problem. Some types of headset applications such as those used by pilots, and other communications devices also use this type of earmold.
Shell:                    The shell mold is used with ear level (BTE) aids with a broad fitting range covering moderate to profound hearing losses.
Half Shell:                       Similar to the shell, but with the upper half of the concha (triangular fossa) removed for comfort and ease of insertion where there may be dexterity issues. The fitting range is for moderate to severe hearing losses.
Skeleton:                 This is a popular application where an inconspicuous mold is desired. It effectively provides a good seal while allowing the concha to be relatively open for greater airflow in the bowl of the ear. The fitting range is for mild to severe hearing losses
Semi Skeleton:               Where there is little or no retention due to a sloping or disappearing concha, this style is ideal. It provides adequate retention where losses range from mild to severe and is similar in structure to the skeleton, but without a full rim, which might otherwise stick out of the concha.
Canal Tip:                                 The helix and concha portions of this style are totally removed, leaving only the portion of the mold from the primary seal inward. If the canal is well defined, a canal tip may be used with a fitting range from mild to severe losses.
Semi Canal:                     Only the lower half of the concha rim is retained to keep the mold in proper position. This tail can be used to assist in removal and is aesthetically one of the most popular earmold styles. The fitting range is for mild to severe losses.

Non occluding earmolds:

Some people term non occluding as some vent path, no matter how small. Others refer non occluding earmolds as partly occluding molds referred to as open molds also. These are developed for patients with unilateral hearing losses for use with cross type of hearing aids. The mold includes a small outside diameter canal portion which allows amplified sound to pass around the earmold & also through the tubing. When used with a single behind the ear hearing aid, the fitting is referred to as ipsilateral routing of signals (IROS). The non-occluding earmolds have an advantage of providing natural hearing plus amplified sound.

CROS-A,CROS-B, CROS-C, IROS, Janssen, free field.

v The CROS & IROS style ear molds are suitable for CROS & IROS hearing instruments fittings. Lucite is the preferred materials, & is available in 3 distinct styles.

v In CROS A & CROS B, the canal portion is built with an extension of plastic finished down as close to the tubing style size as possible. CROS C combines skeleton design with a length of tubing directed into the centre of the canal. This mold is especially recommended for attaching the offside microphone or transmitter in a behind the ear CROS or BICROS fitting.

CROS molds are indicated when it is necessary to significantly reduce or eliminate frequencies below 1000 Hz. The opening of the canal is not occluded, & low frequencies are allowed to bleed off.

v Janssen earmold:

It is named after a dispenser who invented it. This earmold style incorporates the acoustic & retention benefits of the CROS style earmolds, but differs in  that the canal portion runs along the top of the ear canal. It requires a long canal.

v Free field:

A predecessor of the Janssen earmold, the free filed differs from the CROS mold by its more reduced concha ring & bridge area. Since there is no seal, there is always the possibility of increased incidence of feedback. A new non-occluding earmold which is characterized by a wider bridge piece with a select-a-vent installed. The canal portion of the mold is not at the top of the canal, giving the greatest amount of open space beyond the bridge.

Custom plugs

v For swimming

                   Many persons recovering from ear infections or ear surgery, as well as those with chronic conditions such as drainage,must keep their ear canals dry to prevent more severe problems from developing. Ideal for bathing, showering or swimming, swim plugs are simply soft custom earmolds without any bore or tubing.

v Communication molds

            Custom communication molds are developed for radio, aviation, motorcycle, and phone headsets. Our communication line provides maximum comfort that only can be obtained from a custom made ear mold..

---Cellphone
This hands free device is a custom made ear piece that fits right over the earphone (bud), allowing you to use both hands while driving or walking with out having the outside interference. The custom ear piece is done in a soft clear vinyl. This will allow the earphone to have a good tight friction fit and easy to keep clean.

---PP hanger
This is a pacific plantronic ear piece for and airline pilot. It allows them to hear and to communicate to the airport towers. This ear piece is made in a Lucite clear and has an extended bar to hold the microphone. Also available in a vinyl clear material and in many other colors. 

----FBI-TV 
Broadcaster's and police all have this one. This mold comes in two different styles and materials. The first one comes in a body aid style, it has a snap on male adapter, connecting to a coiled tube or straight tube. The second type can be made into a canal tip style. Having the same kind of coil tube or straight tube with out having a male adapter. This one is fixed to the ear mold.

----Motorcycle
For those who have communicating headsets to there motorcycle like the Road king. You can now have a custom made ear piece done for both ears for your existing headset. We can remove the existing earphone and from your custom made ear mold we will connect new stereo drivers (microphone) and embed them into your custom made ear molds. This will allow a better quality of sound and enjoyment. The ear mold is made in a hypoallergenic material for long wear and use.

Radio Ear
This is a custom made way to listen to  MP3 or  I-pods and portable CD player.

v NoiseDefenders

                   
----Shooters Plugs
These molds are for those seasonal hunter's. They are made with a cylinder embedded into the ear mold, which is fully occluding the ear only allowing sound to enter though the cylinder. The cylinder is a device which allows you to hear until a gun has been fired.  This will activate the cylinder diaphragm to close off. Shutting out any harmful Db's. And when relaxed the cylinder will reopen for normal sounds. The ear mold is made of a high grade of silicone material..

----Noise Plugs

                          Having the whole ear concealed helps keep out harmful sounds. The material most used for this would be a silicone type. However, it could also be done in a vinyl material as well.

---- Custom Musicians Earplugs 
                          ER are attenuators, They have the ability to give a flat response to the different frequencies of sounds that are being played in bands, orchestra and concerts. These are generally done in a vinyl material and made in a canal tip style and color code left and right.

----ER 20 Attenuaters
This is a generic type - one size fits all -  however we are able to make a custom tip for these filters and have them made just as small in size and for comfort. 

----Noise Brakers
Noise Brakers are a non-mechanical electronic plug which allows you to still hear and carry on a conversation but will protect the ears from 80Db's and over. There is a small acoustic filter inserted in the chamber of the mold so it has no adjustment.  

                                                                                                                         Techniques to modify the acoustic output of a hearing aid via:

- Venting

-Acoustic Filters or Dampers

-Horn Effects

--- Venting

A vent is a channel drilled in the body of the earmold that connects the lateral surface of the mold with the medial end of the canal. Acoustically there are several purposes of venting:

• Reduction of low frequency amplification.

• To relieve occlusion effect in patients with little or no low frequency hearing loss & to prevent moisture condensation in earmold that would adversely affect the hearing aid performance.

Types of Vents

• PARALLEL

– Parallel vents effectively reduce low frequency energy without reducing highs. Parallel vents are always recommended over the other types and should be used unless otherwise requested or required due to size constraints. The larger the vent bore, the more the low frequencies are reduced.

• DIAGONAL

– Diagonal vents begins at the earmold lateral surface & then intersects the sound bore between the end of the tubing & the end of the mold. It tends to vent sound energy better than parallel vents, but high frequencies are also affected. This may introduce feedback problems and reduce high frequency gain. Diagonal vents are recommended when size restrictions make parallel vents impossible.

• EXTERNAL

An external vent is a V-shaped groove which runs along the bottom of the canal portion of the mould. It is used for patients possessing small ear canals where accommodating 2 bores within the earmold canal is not feasible & only when there is a feedback problem with a parallel vent. The disadvantage of this type of venting is that the external portion of the vent can be clogged by ear wax & moisture.

Occlusion effect and venting

The occlusion effect is not a new phenomenon and has been described here before. Still, it is a serious and continuing problem for some hearing aid users and thus is the kind of topic that merits some repetition now and then.  Sometimes people feel like they're talking in a barrel, that what they're hearing is echoes of their own voice, or that their voice sounds "hollow" or "booming".. People who have a large occlusion effect may also feel a sense of pressure or blockage in the ear when an earmold is inserted.

An occlusion effect occurs when some object (like an unvented earmold) completely fills the outer portion of the ear canal. What this does is trap the bone-conducted sound vibrations of a person's own voice in the space between the tip of the earmold and the eardrum. Ordinarily, when people talk (or chew) these vibrations escape through an open ear canal and the person is unaware of their existence. But when the ear canal is blocked by an earmold, the vibrations are reflected back toward the eardrum and increases the loudness perception of their own voice. Compared to a completely open ear canal, the occlusion effect may boost the low frequency (usually below 500 Hz) sound pressure in the ear canal by 20 dB or more.

This is a real and measurable increase in sound. One way that it can be determined is with a probe-tube microphone (a device that should be used, in my judgment, in just about every hearing aid fitting). A probe-tube microphone consists of a very fine, flexible tube that is connected to various types of sound measurement equipment. The tube is inserted in the ear canal and the audiologist measures the sound levels in the ear canal while the hearing aid user utters some standard vowel (like "ee"). Then, with the tube still in place, an earmold (or hearing aid shell) is inserted in the ear canal, making sure that the tube extends a few millimeters past the earmold tip. Then, with the hearing aid turned off, the audiologist again measures the sound levels when the hearing aid user says the same vowel (at the same loudness level). The difference between the sound levels occurring when the ear is open and when it is closed with a hearing aid is a measure of the amount of the occlusion effect. As I noted above, differences of 20 dB or more are common.

There are basically only two ways to reduce or remove the occlusion effect. The most effective way is to not completely block the ear canal with an earmold. This permits the bone-conduction sound generated in the ear canal to escape the ear the way it is supposed to. When someone is wearing hearing aids, the only way to do this is to create a vent hole in the earmold. For those who are unfamiliar with an earmold vent, it is a hole drilled completely through the earmold from the outer surface to the inner surface. The amount of sound that escapes, and thus the magnitude of the occlusion effect, depends upon the size of the vent. The larger the vent, the more the occlusion effect can be reduced.

                                          The smallest vent is termed a "pressure" vent. By allowing air to enter the ear canal, a "pressure" vent will alleviate the feeling of fullness in the ear that can occur when an ear is completely blocked by an earmold. It does this by equalizing the atmospheric air pressure to that occurring in the ear canal. While a pressure vent will not reduce the occlusion effect or influence the pattern of amplification, it will help a hearing aid user be more comfortable when wearing the aid. Pressure vents are very common in hearing aids, except for smallest completely-in-the canal (CIC) hearing aids. These aids are so chock full of electronics that they have no spare space left to accommodate a vent.

Slightly larger vents will not only begin to reduce the occlusion effect, which is one of our primary goals, but it will also shunt some of the amplified low frequency sounds out of the ear. That is, some of the low frequency sounds amplified by the hearing aid will not be transmitted through the middle ear into the inner ear. Instead, these amplified low frequency sounds in the ear canal will find that the acoustical path of least resistance is out through the vent hole and into the atmosphere, rather than through the middle ear. Thus a vented earmold effectively reduces the degree of low frequency amplification delivered to a hearing aid user. These sounds are simply shunted out of the ear canal. The acoustical consequence of this action may be positive or negative depending upon the audiologist's fitting goals. It will be positive for those people with little or no hearing loss in the low frequencies, for whom little or no amplification of the low frequencies is required, but not so good for people with more severe hearing losses across the audiogram. The larger the vent, the greater the reduction in the occlusion effect and the more amplified low frequency sounds that are shunted out of the ear canal.

Even though vents will reduce the occlusion effect and can make wearing a hearing aid a bit more comfortable, there are several potential downsides. Hearing aid users with moderate-to-severe hearing loss or greater frequently experience acoustical squeal when their earmolds are vented. The sounds that escape from the vent are picked up again by the hearing aid microphone and re-amplified, thus beginning the acoustical oscillations that produce the feedback squeal. On the positive side  people with more severe hearing losses generally do not require vents, except for, perhaps, a pressure vent and thus vent produced feedback is not a problem. Insofar as the occlusion effect is concerned, however, they are less likely to be bothered by it than people with lesser degrees of hearing loss. The people who seem most susceptible to the occlusion effect are those with relatively good hearing at the lower frequencies.

                       Another way of resolving occlusion effect is by decreasing the spatial placement between the tip of the instrument  and the tympanic membrane ( deep canal fittings), thus limiting the opportunity for vibrations.  Proper deep fitting techniques  can achieve such desirable results with little or no occlusion effect.

• Disadvantages of venting

– Acoustic Feedback

– Reduction in the potentially beneficial effect of directional microphones

– Exaggeration of signal processing delays

The following table provides guidelines for vent selection in relation to the patient’s hearing loss:

			Vent size(mm)
Hearing loss in the range 250hz to 1khz	Non occluding	4-2	2-1	1-0.5	No vent
Normal	·
Mild		·
Moderate			·
Severe				·	·
Profound					·

ü Filters/Dampers

• These reduce the amplification in the medium frequency range. There are various placements of the dampers e.g. at the tip of the hearing aid tube, tip of earmold tube, deep within the earmold tube, tip of the earmold. The latter is considered to be the best but highly impractical because wax or debris will clog the mesh hence junction between the hearing aid tube & earmold tube is recommended.

Several types of damping materials are used. Knowles acoustic dampers are the most convenient damping system. These are made in a metal housing with a color coded mesh screen at one end. There are 6 Knowles dampers available: 680 (white), 1000 (brown), 1500 (green), 2200 (red), 3300 (orange) & 4700 (yellow). The higher the damper value the stronger the effect of attenuation. However too much damping may have an adverse effect on the efficiency of the transmission line & result in increased battery drain. Other damping materials such as lamb wool, sintered steel pellet, & the star damper are not commonly used now.  

ü Horn Effects

It is known from musical acoustics that belling of a tube will enhance a high frequency signal passing through the tube. The reverse is also true in that the narrowing of the end of the tube will reduce the high frequency components.

• Hence using horn tubes in earmolds boost high frequency amplification

• Reverse Horns reduce high frequency amplification

Need of horns- the modern small receiver is a high impedance source. This means that it generates high sound pressure, which can move only a small volume of air. The eardrum is a moderate impedance load. A low impedance load responds to low pressure, but requires large air volume movements. An impedance “transformer” is required to transfer energy from the receiver to the ear efficiently. A horn bore is such a transformer. It works as follows: the high pressure from the receiver moves a small volume of air in the small diameter of the tube. These in turn, moves a larger volume of air in the next larger bore of the tube & the pressures drops accordingly, & so on progressively until the conditions required by the eardrum are met. The improvements in frequencies around 6000Hz is about 10-12 dB & depends on the ratio of the diameter of the tube at the receiver & the diameter of the bore at the earmold canal end. The bore does not need to be circular to produce the horn effect. A very useful aspect of the horn’s response is that there is a boost in signal at 2.7 kHz that will compensate for the insertion loss. This helps to achieve a more natural sound.

Libby horn (1980) developed a one-piece earmold tube with varying diameter. This smooth tube of internal stepped-bore construction, commonly known as Libby horn tube, is available in 3mm & 4 mm sizes, & is used quite frequently for high frequency hearing losses.

Small ears may not require the use of the horned tube at all. As was already mentioned, acoustic resonance occurs as a result of the tube / ear-canal impedance mismatch. In small ears, the impedance of the ear canal & eardrum may be close to the impedance of the tube, so the hearing aid response may be satisfactorily smooth. The other types include killion molds, continuous flow adapters (C.F.A) and resonator earmolds. 

ü Tubing:

The two most commonly used tubing sizes are the # 13 medium & # 13 thick for hearing aids with separate earmolds. Acoustically, only the inside diameter, which the tubing number identifies, has a significant effect on sound transmission. However, the thick wall tubing is often used to reduce the possibility of sound radiation that could cause acoustic feedback in high-gain aids.

	Normal inside diameter		Normal outside diameter
Size	inch	mm	inch	mm
NAEL sizes
No 9	0.118	3	0.158	4.01
No 12 standard	0.085	2.16	0.125	3.18
No 13 standard	0.076	1.93	0.116	2.95
No 13 medium	0.076	1.93	0.122	3.10
No 13 thick	0.076	1.93	0.130	3.30
No 14 standard	0.066	1.68	0.116	2.95
No 15  standard	0.059	1.50	0.116	2.95
No 16 standard	0.053	1.35	0.116	2.95
No 16 thin	0.053	1.35	0.085	2.16
Other sizes
No 13 double wall	0.076	1.93	0.142	3.61
No 15 thick wall	0.059	1.50	0.140	3.56
1/32 inch	0.031	0.79	0.094	2.39

The above are Standard sized earmolds tubing that have been established by the national association of earmold laboratories (NAEL) (Blue, 1979).

 Recent Advances in earmold technology

Microsonic is the leading manufacturer of custom earmolds made with laser technology. Their  decades of custom earmold manufacturing experience have been transferred into Micro-Fit process. Micro-Fit uses laser technology integrated with specialized 3D software to produce high-quality custom earmolds.

Some key advantages of using our Micro-Fit™ process are:

·         High accuracy – dimensional tolerance is low as low as .0005”

·         Best fitting – thanks to 3D scanning technology and sophisticated earmold design software, earmolds are tailored to comfortably fit into patient’s ear

·         Repeatability – exact replica of missing/broken molds can be produced within hours

·         Hypoallergenic materials

·         Superior sound bores and vents

·         Variety of surface finishing options

·         Most earmold styles including open-fits

The microfit process

Leading earmold manufacturing companies

v  Microsonic

v Westone

v The Earmold Company

v Earmold Concepts

v Earmold Australia

Articles

a) Open earmold fittings for improving aided auditory localization for sensorineural hearing losses with good high-frequency hearing.

Byrne D, Sinclair S, Noble W, Ear & Hearing,  1998 Feb; 19(1):62-71.

National Acoustic Laboratories, Chatswood, NSW.

OBJECTIVE:  They  tested the hypothesis that the use of nonoccluding earmolds for hearing aid fittings could optimize auditory localization in the vertical plane for people with moderate, low-frequency hearing losses and good hearing at frequencies above 4000 Hz. This benefit was expected to arise from leaving the pinna unobstructed and by optimizing hearing (unaided) for frequencies above the hearing aid's limit.

DESIGN: Twenty-two participants had hearing losses greater than 30 dB over the range 250 to 2000 Hz and had minimal losses (< 30 dB) at 6000 Hz and 8000 Hz. Their auditory localization was tested, using a horizontal arc and a vertical arc of loudspeakers, when listening unaided and when fitted bilaterally with Behind The Ear hearing aids with three earmold types--closed (occluded), open (partly occluded), sleeve (nonoccluded).

 RESULTS: Localization of vertical plane sound sources was significantly poorer for the closed earmold condition than for unaided. The open and sleeve conditions were better than the closed condition, and, for the sleeve earmold, vertical localization was almost equal to that unaided. The capacity to benefit from using open rather than closed earmolds was related to hearing level; people with the best hearing at 4000, 6000, and 8000 Hz received the most benefit. There was limited evidence that open earmolds also can be advantageous for some aspects of horizontal plane localization.

CONCLUSIONS: Nonoccluding earmolds optimize aided vertical localization for hearing aid users with good high-frequency hearing. The "sleeve" earmold, so far used only in research, may be a useful clinical option.

b) The efficacy of open molds in controlling tinnitus.

Munhoes dos Santos Ferrari G, Sanchez TG, Bovino Pedalini ME, clinical speech and hearing therapy

University of São Paulo.

Hearing aids may be an option to improve tinnitus and hearing loss.

AIM: to evaluate tinnitus after one month use of BTE hearing aids with open molds and pressure vent molds in patients with symmetric sensorineural hearing loss.

METHODS: 50 patients seen at the Clinic who presented bilateral tinnitus and hearing loss underwent a randomized blind crossover clinical trial: 26 first used BTE hearing aids with open molds, and the remaining 24 first used pressure vent molds. After 30 days using the first mold and a wash-out period, the type of earmold was changed and was applied for another 30-day-period. Tinnitus evaluation was done qualitatively (improved, unchanged and worsened) and quantitatively (variation on a numeric scale from 0 to 10).

RESULTS: 82% of the cases reported improvement of tinnitus with at least one type of earmold; there was no significant difference in the reduction of discomfort due to tinnitus in the quantitative and qualitative evaluations. Although similar tinnitus control was obtained with both methods, 66% of the patients preferred the open mold.

 CONCLUSION: In a short-term evaluation improvement of tinnitus by the use of hearing aids does not depend on earmold ventilation.

c) Effect of the Earmold on Speech Intelligibility in Hearing Aid Use

William R. Hodgson & CharlesMurdock,Jr, Journal of Speech and Hearing Research, American Speech-Language-Hearing Association, June 1970, Vol-13, pg 290-297. University of Kansas Medical Center, Kansas City, Missouri

---Aided speech intelligibility scores were obtained in quiet and in noise from 18 subjects with high-frequency sensorineural loss, using standard, vented, and open earmolds.

---Results showed that scores obtained through the open earmold were superior to those obtained through the standard earmold, both in quiet and in noise.

---There were no significant differences between the standard and vented earmold, or between the open and vented earmold. Twelve of the subjects preferred the open earmold.

d. Occlusion effect of earmolds with different venting systems.

Kiesslin J, Brenner B, Jespersen CT, Groth J, Jensen OD., 2005

Source

Department of Audiology, Justus-Liebig University Giessen, Germany.

                        

                                                                     In this study the occlusion effect was quantified for five types of earmolds with different venting. Nine normal-hearing listeners and ten experienced hearing aid users were provided with conventional earmolds with 1.6 and 2.4 mm circular venting, shell type earmolds with a novel vent design with equivalent cross-sectional vent areas, and nonoccluding soft silicone eartips of a commercial hearing instrument. For all venting systems, the occlusion effect was measured using a probe microphone system and subjectively rated in test and retest sessions. The results for both normal-hearing subjects and hearing aid users showed that the novel vents caused significantly less occlusion than the traditional vents. Occlusion effect associated with the soft silicone eartip was comparable to the nonoccluded ear. Test-retest reproducibility was higher for the subjective occlusion rating than for the objectively measured occlusion. Perceived occlusion revealed a closer relationship to measured occlusion in the ear in which the measured occlusion effect was higher ("high OE" ear) than in the "low OE" ear. As their results suggest that subjective judgment of occlusion is directly related to the acoustic mass of the air column in the vent, the amount of perceived occlusion may be predicted by the vent dimensions.

e. Effect of venting the ear mold on speech discrimination in masking noise

Brügel F, Schorn K, Fastl H., 1991

Source

Klinik und Poliklinik für Hals-, Nasen- und Ohrenkranke, Ludwig-Maximilians-Universität München, 1991

In this study the importance of in situ measurement during the fitting of a hearing aid is clearly emphasized. Reliable evaluation of the real ear gain can be achieved only with this method, and hence the assessment of the advantages of earmold modifications on the hearing aid. In particular, the gain can be evaluated by the person fitting the aid. The insertion of a vent into an earmold raises the listening comfort of the hearing-impaired person. The speech intelligibility in background noise may also improve. They  analysed the effect of earmold venting on speech intelligibility under different background noise conditions. They found that venting improves the speech intelligibility, especially in background noise simulating modulated speech. Their example clearly demonstrates the importance of an exact control of the hearing aid fitting by the physician. In one case a vent ended at the ear canal wall so that no improvement of hearing comfort could be expected. A new earmold was made and the effect on insertion gain was demonstrated when enlarging the vent step by step.

References:

o   Robert E. Sandlin; hearing aid amplification; 2^nd edition; 2000, chapter 4, pg- 137-170.

o   William R. Hodgson & CharlesMurdock.Jr; Effect of the Earmold on Speech Intelligibility in Hearing Aid Use; Journal of Speech and Hearing Research; American Speech-Language-Hearing Association, June 1970; Vol-13; pg 290-297.

o   The hearing review.com

o   www.microsonic.com

o   www.westone.com

o   www.minervalabs.co.uk

o   www.Earmoldconcepts.inc

o   www.earmoldaustralia.com