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Hearing Aids
Dr. Holston Mid Term
| Types of Earmold Materials | Lucite/Acrylic, Polyvinyl Chloride/Vinyl, Silicone, Lucite with a Soft Canal, Open Tube Fittings |
| Lucite or Acrylic | Most durable of the materials. Clear or skin toned color makes it cosmetically appealing. Easiest to modify in-house. Good for mild up to moderate/moderately-severe loss, but use with greater loss may result in feedback. Easiest to clean. |
| Is Lucite or Acrylic used for children? | Not a particularly good choice for children due to hardness and chance of child's ear being injured if he falls. |
| Polyvinyl Chloride or Vinyl | Soft material that provides comfort and better sound retention than acrylic. Can be used with practically any degree of loss. |
| Is Vinyl used for children? | Often used with children because their molds are replaced fairly often anyway due to growth of their ear (about every six months). |
| Silicone | A soft material that provides comfort and good sound retention for a severe loss. More durable than vinyl in that it maintains softness and does not shrink appreciably, however, it can be discolored in some patients. |
| Disadvantage of Silicone | It is difficult to glue anything to this material and tubing is sometimes hard to retain in the sound bore. Tube locks provide some help with this problem. |
| Disadvantage of Vinyl | Downside is that in some patients material hardens and shrinks over time which requires more frequent replacement. |
| Lucite with a soft canal | A combination of a lucite concha with a soft (vinyl or silicone) canal, provides the better sound retention of a soft mold with only the more cosmetically appealing lucite showing from the outside. |
| Open tube fittings | Not an earmold style, but used increasingly in place of ear molds in patients with high frequency or mild hearing loss. |
| Style of Earmold | Regular, Full Shell, Half Shell, Skeleton, IROS/CROS, Canal |
| Regular | Full mold containing entire concha volume, used with severe or profound loss due to excellent retention. Can be used with either regular tubing or a snap ring connection. Not terribly popular due to the bulk size and appearance. |
| Full Shell | Good retention for severe to profound loss, but less bulky and more cosmetically appealing than a regular mold. A popular choice for patients with a severe or profound loss. |
| Half Shell | Similar to a shell earmold with the top portion of the concha removed. Easier to insert than full shell earmold, but doesn't have quite the sound retention. Could be used for losses up to severe, but not a profound loss. |
| Skeleton | Basically a shell ear mold with the middle of the concha cut out and a skeleton of the shell remaining. Popular due to comfort and appearance. Can be used with mild to moderate loss, possibly moderately severe. |
| CROS/IROS | A non-occluding earmold designed for CROS hearing aids or open fittings with normal hearing in the low-mid frequencies and a loss in the high frequencies. |
| What does the CROS earmold look like? | Looks a little like a skeleton mold with the canal portion consisting of the tubing surrounded by a small amount of earmold material. In many instances, CROS/IROS molds are now being replaced by slim or open-fit tubing. |
| Canal | An earmold consisting of only the canal portion of the impression. At one time reserved for more mild/moderate losses, but with improvements in retention ability from soft earmold material, csn be used on losses up to severe in some cases. |
| Earmold Modifications | Venting, tubing, bores, length of canal |
| Reasons for Venting | Pressure equalization, increased comfort from letting the ear aerate, allows air-conducted low frequencies to escape, allows bone-conducted low frequencies to escape (reduced OE), allow unamplified signals to pass unobstructed to the eardrum. |
| Types of Vents | Diagonal, parallel, trench |
| The bigger the vent the more ____ are attenuated. | Low Frequencies |
| Small pressure vents are used for: | Pressure equalization and provide minimal modification of the frequency response , particularly if they are long as well as small in diameter. |
| What happens when the diameter of the vent is wide and the length of the vent is short? | There will be more of a low to mid frequency cut-off. |
| What should the vent be like for maximum reduction of gain at 1000 Hz and below? | The vent should be as wide in diameter and as short in length as possible. |
| Which vent is usually preferable to other vent types? | A parallel vent is usually preferable to other vent types. They run parallel to the bore. |
| If space dictates that a diagonal vent is used, what is important to keep in mind? | The point at which the vent intersects the bore is important. |
| If you want the diagonal vent to act like a parallel vent and reduce low frequency gain: | The vent should intersect the bore as near to the tip of the earmold as possible. |
| For a high frequency loss or for a flat audiogram the vent should intersect the bore: (prevent reduction of HF gain) | As near to the tip of the ear mold as possible. The vent should be drilled as far back, toward the end of the bore as possible. |
| If you want reduction of high frequency gain, the diagonal vent should be: | drilled as far back toward the beginning of the bore as possible (away from the tip of the ear mold). |
| Reduction of low frequency gain is accomplished through the vent being: | Short and wide. |
| For a reverse slop hearing loss, the vent should be: | drilled as far back toward the beginning of the bore as possible (to reduce high frequency gain). |
| Tubing is sized: | #12-16 with variation in the diameter. |
| Regular tubing is: | #13 tubing with variation in thickness. |
| A Libby Horn is wider than a standard tube and is primarily used to: | enhance amplification in the high frequencies. |
| When using a slim tube: | the gain of the hearing aid must be adjusted higher due to the decrease from sound going through the small diameter opening. |
| When can a CFA tubing be used? | It can be used to increase either high or low frequency gain. |
| Bores include: | Standard Bore, Belled Bore, Reverse Bore |
| Standard Bore | Drilled so that standard 13 tubing fits snugly with no leakage. |
| Belled Bore | bore widens near where sound exits into the ear to give a "horn effect" and enhance high frequencies. |
| Reverse Bore | Bore is wide at the entrance, but narrows as sound passes toward entrance into the canal. |
| Why does a reverse bore have a reverse effect of a belled bore? | The reverse bore tends to reduce high frequency gain. |
| Short Canals | Used for enhanced high frequency response and lower gain. |
| Long Canals | Used to enhance overall gain, particularly in low frequencies. |
| Gain | The amount, in decibels, by which the SPL developed by the hearing aid in the coupler exceeds the SPL in sound field. |
| Gain (plain terms) | The difference between the level going into the aid versus what comes out after the sound is amplified. |
| HF Average Full-On Gain | The average gain at 1000, 1600, and 2500 Hz when the volume control or the aid is turned as high as it can go. |
| Reference Test Gain Definition | A measure of gain below the aid's full on position, which allows for a more realistic appraisal of the way hearing aids might perform on an actual patient. |
| Reference Test Gain (Approach) | The gain control of the aid is set to amplify an input signal of 60 dB SPL to a level 17 dB below the OSPL90 value. Average reference test gain is established from average values at 1000, 1600, and 2500 Hz. |
| Frequency Response | The frequency range of amplification from a hearing aid expressed in Hz, from the lowest to the highest frequency amplified. |
| Harmonic Distortion | The distortion created when harmonic frequencies are generated in an amplification system. This is usually expressed in percent distortion. |
| Output Sound Pressure Level | The newer term for maximum output of a hearing aid; the highest SPL to leave the receiver of the aid, regardless of the input. |
| HF Average OSPL | The average maximum output of the aid, calculated by averaging OSPL 90 at 1000, 1600, and 2500 Hz. |
| Equivalent Input Noise Level | The inherent noise level within a hearing aid with the input signal turned off and the hearing aid set at the reference-test-gain level. |
| Amplitude Distortion | The presence of frequencies in the output of an electroacoustic system that were not present in the input, resulting in a disproportional difference between the input and output waves. |
| Frequency Distortion | An inexact reproduction of the frequencies in a sound wave. |
| Battery Current Drain | Measured with the volume control of linear hearing aids set to the reference test gain position and with compression aids set to full-on gain. |
| How is the battery current drain measured? | A 1000 Hz tone is introduced into the free field at an intensity of 65 dB SPL and battery current drain is measured. |
| ITE Dead/Weak: First Thing | Check to see if the battery is good. |
| ITE Dead/Weak: Checking for cerumen in the receiver | Using an otoscope, you should see a stainless steel nubbin with a mesh screen bottom when looking down the receiver tube. If wax is covering the receiver, remove with either a wax loop or suction. |
| ITE Dead/Weak: Checking for cerumen in the microphone | Using an otoscope, you should see a stainless steel nubbin with a mesh screen bottom. If wax is covering the receiver, use suction for removal. |
| What are the two things that affect HAs the most? | Moisture and cerumen |
| ITE Dead/Weak: Cleaning battery contacts | If battery contacts appear corroded, clean gently with a Q-tip dipped in 90% alcohol. |
| ITE Dead/Weak: After cleaning battery contacts | Increase tautness of battery contacts for better contact. |
| ITE Dead/Weak: Checking program button and volume controls for intermittency | Spraying a small amount of contact cleaner on these controls can sometimes provide temporary relief. |
| ITE Causing Feedback (1) | Check patient's ears for excessive cerumen (if they are occluded with wax the sound bounces off the cerumen instead of going through the TM). |
| ITE Causing Feedback (2) | Check to see if the patient is inserting the aid properly and that the aid still fits them properly. |
| ITE Causing Feedback (3) | Check to see if the receiver tube has fallen down into the shell of the aid. |
| ITE Causing Feedback (4) | Check for cracks in the faceplate or shell of the aid. |
| ITE Causing Feedback (5) | Check to see that microphone tube (much like receiver tube) is still in place. |
| ITE Causing Feedback (6) | If aid continues to squeal when you turn it on and put your finger over the receiver, you may have internal feedback and the aid should be sent back for repair. |
| If feedback is internal and you put your finger over the receiver the whistling will | not stop. |
| If feedback is external and you put your finger over the receiver the whistling will | stop. |
| ITE Causing Feedback (7) | Run new feedback test on aid. |
| Patient complains the ITE/BTE Aid Sounds different (3 things) | Perform listening check to see if the aid sounds distorted or weak. Check for wax in vent (of the ear mold), which could cause increased occlusion. If available, perform electro-acoustic check of Harmonic Distortion. |
| BTE Dead/Weak: First Thing | Check to see if the battery is good. |
| BTE Dead/Weak: Checking for cerumen in ear mold using an otoscope. | If the wax is occluding the ear mold, remove with either a wax loop, suction or remove tube from ear hook and blow out with a tubing blower. |
| BTE Dead/Weak: Checking for shrinkage in the ear mold tubing. | If the tubing diameter has shrunk and the tube is hard, replace. The tubing can shrink because it's vinyl (will restrict HFs). Should be replaced every six months. |
| BTE Dead/Weak:Check for moisture in tubing between the mold and the ear hook. | If present, remove the ear mold from the ear hook and blow out moisture with a tubing air blower. |
| If the BTE aid is dead, the ear mold can be checked as a source of the problem by removing it from the ear hook. | If the aid squeals or works once the ear mold has been removed, the problem is likely in either the ear mold or the tubing. |
| BTE Dead/Weak: Check filter in the ear hook, which can be clogged by moisture or dirt/dust. | If the aid is still not working after the removal of the ear mold, remove ear hook (if possible); if the aid begins to squeal or is working via listening check, the problem is in the ear hook filter. |
| BTE Dead/Weak: If the problem is in the ear hook filter, how is it resolved? | Replace the ear hook or if no new ear hook is available, remove the filter. |
| BTE Dead/Weak: Checking program button and volume controls for intermittency. | Spraying a small amount of contact cleaner on these controls can sometimes provide temporary relief. |
| BTE Dead/Weak: Checking microphone openings or filter covers. | If clogged or dirty, either replace or suction out. |
| BTE Dead/Weak: Cleaning battery contacts. | If battery contacts appear corroded, clean gently with a Q-tip dipped in 90% alcohol. |
| BTE Dead/Weak: After cleaning battery contacts. | Increase the tautness of battery contacts for better contact. |
| BTE Causing Feedback (1) | Check patient's ears for excessive cerumen. |
| BTE Causing Feedback (2) | Check for cracks in ear mold, tubing or ear hook. If detected, replace. |
| BTE Causing Feedback (3) | Check to see that ear mold is inserted properly or that the ear mold is still appropriate in size for the patient's ear. |
| BTE Causing Feedback (4) | If you remove the ear hook, place your finger over the receiver opening, and the still squeals, you probably have a loose or deteriorated receiver tube or some other problem causing internal feedback. A factory repair will be necessary. |
| BTE Causing Feedback (5) | Run a new feedback test to see if this will eliminate the problem. |
| Why do many BTE HAs have filters in their ear hooks? | Reduces the resonant peaks in the frequency response that can be caused by the tubing. |
| Coupler Mic a.k.a. measuring mic | Measures the output of the HA |
| Reference Mic (sits in the box) | Monitors the SPL reaching the HA from the loudspeaker |
| Where should the reference mic be situated? | The reference mic should be as close to the HA but not touching it. Monitors signal coming out of the loudspeaker → verifit will change the signal coming out of the speaker to match it to what is intended to reach the HA. |
| Signal Processor | the measured signal is compared to the known input signal. Graphs are then generated using those comparisons. |
Created by:
jennyhams
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