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33 Cards in this Set
- Front
- Back
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analog-non-programmable
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adjusted w/ small skrewdriver
mic-->sig path-->reciever |
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analog non programmable disadvantages and advantages
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DIS: adjustments not precise
limited adjustments available advanced processing not available AD: can make adjustments w/o electricity=anywhere |
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analog-programable
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mic-->sig path (<--digital)-->receiever
computer interface adjusted w/ interface +comp software |
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analog programable advantages and disadvantages
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AD:; more precise than analog non-programmable
DIS: adjustments not precise as digital limited adjustments available advanced processing not available |
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digital programmable
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analog transduccers
digital processing (converts electrical voltages to digital numbers) |
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Digital programmable advantages and disadvantages
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AD: best precision (if mid to high end)
advanced processing available Limitations: low-end digital-limited adjustments (but cheap) additional distortion if not well designed |
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2 types of feedback management strategies
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1. notch filter
2. feedback cancelation |
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notch filter
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presently found in low end HA's
disadvatange: reduces gain of input signal (ex. speech) |
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feedback cancelation
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aid detects oscillation (feedback)
aid generates signal 180 degree out of phase partially cancels feedback |
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expansion
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opposite of compression
-help turn gain down really fast for a really low input -purpose: to minimize amount of ampt below CT |
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why would you want to do expansion
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potential problem of conventional WDRC gain max below
-amplifies mic noise -may over amplify soft environmental soudns (annolying) |
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how can expansion help?
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reduces mic noise reaching the listener
expansion also reduces low-level environmental noise |
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in expansion:
raise input level= lower input level= |
raise input level=gain up
lower input level=gain down |
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noise reduction: modulation information
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will monitor modulation pattern in each channel separately--> if it detects noise in a channel it will reduce gain in that particular channel
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advantages and disadvantages of modulation information noise reduction
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DIS: hard to totally isolate speech, research doesn't suggest better speech understanding
AD: ease of listening effects |
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frequency lowering (list)
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fq transp
fq compression |
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frequency compression
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lectures on fq compression
-takes higher pars ot signal and compresses them so that they are shaping the same fq space |
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identity parts of earmold
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practice!
tubing canal stalk vent sound bore helix lock bends (1st and 2nd) |
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appropriate ranges for skeleton and full shell molds
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skeleton: less than 60-65 dB
full shell molds: greater than 60-65 dB |
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earmold-hard acrylic (AD and DIS)
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AD: durable
easy to make mod inexpensive DIS may be more prone to feedback slight risk of harm from breakage (esp kids) |
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earmold-soft AD and DIS
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AD:
comfortable when tight fit needed less prone to feedback than hard no risk of breakage in ear DIS: diff to modify and change tubing discolors, hardens less durable than hard=more fq replacement |
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earmold-SILICONhypoallergenic AD and DIS
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silicon (semi soft)
DIS: low incidence of allergic reactions diff to modify cannot glue tubing |
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earmold- poly-ethylene (HARD)
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AD: best for hypoallergenic
easy to modify (grind/drill) DIS: ugly |
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earmold acoustics main categories list
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venting
dampers sound bore |
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venting
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low fq
manipulations primarily affect fq less than 750 Hz |
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dampers
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mid fq (primarily 1-2 kHZ)
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sound bore
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high fq (primarily 3-6 kHz)
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venting and gain
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efect of increasing vent diameter loose more primarily < 750 Hz?????
I mm presure vent ????? |
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decrease vent size =
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decrease sound coming in
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diagonal vents
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decreases high fq
-up to 10 dB above 1 kHZ -intersection close to outside is the worst increased likelihood of feedback |
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where do you place dampers?
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usually place in earhook but can also be placed:
BTE tubing ITE Sound bore greater effect with damper further down the transmission line (ex. toward earmold) |
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sound bore specifics
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varying diameter of sound bore affects high fq response (primairly 3-6 kHz)
-the larger the diameter the more gain in high fq 2 ways: 1. acoustic horn: 9 dB better than standary tubing 2. large bore diameter: max 6 dB better than standard tubing |
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vent size on transmission of unamplifed sound through vent
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as vent size changes the attenudation (reduction) of sound getting into the ear canal from outside changes high fq more affected (decreased more) than low fq
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