Hearing Assistive Technologies

acoustics

study of sound and perception

how sound behaves in a given space

noise

any unwanted/interfering sound

signal

the sound you want to listen to

signal to noise ratio

distance

from sound source to ear

reverberation

(echo)

amount of time it takes a sound to decrease by 60 dB after the source has stopped

measured in seconds

noise

any sound that interferes with the signal

tends to carry a lot of low frequencies which “mask” softer high frequency speech sounds

ANSI standards: <35 dB HL (unoccupied class/room)

ASHA standards: <30 dB HL (unoccupied class/room)

sound level meter: has 3 scale for different purposes… ‘A’ scale is most common

signal to noise ratio S/N

equation of signal strength vs overall noise, often related to distance from the speaker/source

inverse square law

inverse square law

signal decreases by 6 dB for every doubling of distance

echo

this is created as sound bounces off of hard surfaces

soft surfaces absorb sounds

size and shape

sound interacts with what and what of a space?

reverberation time

measurement of time it takes for a sound to dissipate/decrease by 60 dB HL

hearing assistive technologies (HAT)

only the DHH students can hear it

connect to personal technology (hearing aids or cochlear implants)

can be used with ear level receiver (looks like a hearing aid)

can be used with a receiver unit and headsets

classroom audio distribution systems (CADS)

used as a “mini” PA system in the classroom

beneficial to many kids for many reasons

only beneficial to DHH kids with very limited hearing loss

not beneficial in a reverberant room

purpose of HAT

eliminates distance between the speaker and the listener (especially because hearing aids and cochlear implants are near field devices)

overcomes noise competing with the speaker’s message

provides direct transmission which eliminates factors of reverberation

benefits of HAT

increased speech perception/word recognition (better reception of voiceless sounds)

decreased listening fatigue, anxiety, and “cognitive load” (easier to hear/distinguish similar words, new vocab, and better ability to follow directions)

decreased vocal strain for teachers

increased use of prosodic information from the teacher (duration, intensity, and pitch)

increased perception of humor, sarcasm, word emphasis, etc

is important for understanding speech

proper use of HAT

microphone placement should be within 4-6 inches of speaker’s mouth, centrally faced, and avoid letting it rub on clothing or touch jewelry

teacher must repeat, rephrase, or summarize other student’s comments

give microphone to students for extended comments OR use a pass around microphone

use for small group work if possible

other applications of HAT

give to presenter for assemblies or field trips

connect to computer for listening instead of headsets

connect to smartboard for media presentations

use for after school activities

adults use for group meetings, restaurants, exercise, sports, work, conferences

types of HAT transmission technologies

FM (frequency modulation)

DM (digital modulation)

remote microphones using 2.4 GHz transmission

bluetooth

infrared

FM

fixed signal transmission frequency

DM

frequency hopping to avoid interference

DM transmission

is like wifi, you can pull up numerous wifi accounts in your area

once you connect to your account, there is no interference from nearby wifis

all operate independently

FM systems

transmitter, cord, and microphone

transmitter and receiver must be on the same frequency (transmitter can send to more than any/all receivers on same channel)

can transmit outside of the confines of the classroom

must carefully plan frequencies in buildings with multiple systems so they don’t cross over

frequencies are protected by the FCC but sometimes there can interference (CB, bus radios, airplane transmissions, walkie-talkies)

interference can also occur from computers and fluorescent lights

DM (roger) systems

digital modulation allows system to “hop” frequencies as it searches for a clear signal (channel)

transmitter and receiver must be paired/synced

can accommodate multiple transmitters paired to one receiver for team teaching

will not bleed over into other rooms

not impacted by computers, lights, etc

many systems can be used as teacher mic, interview mic and conference mic (system recognizes position and automatically adjusts to new function)

remote microphones

are a type of DM system

bluetooth transmission (2.4 GHz)

less expensive than FM transmitter and two receivers

rechargeable or disposable batteries

may have less transmission distance than FM/DM

system may “drop out” and need to be re-paired

great for car, sports, restaurants, work, family life

types of remote microphones

roger partner mic (phonak)

oticon connect clip

signia streamline mic

widex com-dex

resound micro-mic (mic only)

resound multi-mic (has headset, port, becomes table mic, etc)

bluetooth

resound

can connect to phone, MP3 player, etc

can connect to TV and computer

allows user to answer phone in both devices simultaneously (hear better with two ears rather than one, can use phone as a remote microphone in noisy environment)

are allowed to connect later if patient didn’t want it earlier

infrared

requires “line of sight” for light transmission

used primarily in CADS

does not bleed over into other systems

can experience interference in room with bright sunlight

if any object, person, or thing blocks the light transmission, the sound cuts off

CADS considerations

not recommended for children with more than a mild hearing loss

can be used with CI students if placed within 3 feet of child

teacher can hear herself and is less likely to forget to unmute

other students benefit and can be used specifically for these populations: ADHD/ADD, ELL, transient middle ear problems, and auditory processing disorders

loop systems

these use telecoil

sometimes called an audio induction loop

provides a magnetic, wireless signal that is picked up by the hearing aid when it is set to T (telecoil)

system uses: microphone to pick up the spoken word, amplifier which processes the signal, and the loop cable (a wire placed around the perimeter of a specific area)

benefits of a hearing loop

cuts out unwanted background noise

no need to use a receiver/headset

sound goes directly into the hearing aid

can be used by anyone with a compatible hearing aid

it is inconspicuous (can’t see it, usually under carpet or around perimeter of room)

cost effective

any number of users can use the system

speech to text

also known as automatic speech recognition (ASR)

commonly labeled as subtitles or captioning

pre-recorded items have subtitles/captions that have been edited for accuracy

are “live”

software is matching the speaker’s voice to the most probable word

accuracy can be highly affected by rate of speech, pronunciation, accent, and content specific vocabulary

good tool for person’s who are listening for verbal information and just needs back-up for missed information

computer assisted real time translation (CART)

can be in person or remote

considered the “gold standard” for access

trained transcriptionist types everything word for word

often missing capitalization and punctuation

running transcript off event

needed for full access for persons who are not relying on hearing and using ASR to verify or fill in missing info