Venting Flashcards
Does physical modification of the earmold and soundbore change the final output intensity and frequency response of the device?
Yes
What frequencies does venting primarily effect?
Below 1.5 kHz
What is the purpose of venting?
Allows amplified lows to escape
Reduces the occlusion effect
Allows unamplified signals in
Allows aeration of the canal and pressure release
What is the vent effect?
Anything that allows the exchange of air between the canal and outside air
What results in a vent effect?
Earmold with drilled vent bore
Open dome
Loosely fit closed or power domes
Earmolds with slit leaks (poorly fit or dynamic EAC)
Does the air inside the vent have an acoustic mass?
Yes
It takes energy to overcome this mass
Do high frequency signals have enough energy to overcome the inertia of the vent?
No
Do low frequency signals have enough energy to overcome the inertia of the vent?
Yes
They can easily move through
Do larger vents release more low frequency output?
Yes
Open is used for normal hearing, semi-occluded is used for worse, etc.
Do vents also allow low frequency signals generated inside the ear canal to escape?
Yes
If it doesn’t it results in an occlusion effect
When are occlusion effect complaints common?
When someone has low frequency thresholds better than 50 dB HL
What are some of the most noticeable vocalizations for the occlusion effect?
“ee” and “oo”
Baby genie is teeny tiny
How does the occlusion effect work?
The skull transduces low frequency energy generated by the voice
The BC signal becomes trapped in the EAC
Can hollow earmolds help with the occlusion effect?
Yes
The impact of the vent diameter is more pronounced in a hollow mold that a solid mold of the same vent diameter
When are custom non-occluding earmolds fit (thin rod in ear)?
CROS devices for retention but access to normal hearing
Hearing sensitivity is normal in the lows
Can the occlusion effect also be managed by stabilizing the device in the bony canal?
Yes
Needs to extend past the second bend to reach the bony canal
Does venting allow low frequency environmental noise to travel directly to the eardrum without amplification?
Yes
Called direct signal
What are the limitations of low frequencies going through the vent?
Can mask amplified high frequency signals
Digital sound cleaning does manage unamplified direct signals (noise)
How much louder does the amplified signal need to be to dominate the unamplified “direct” signal?
20 dB SPL
What happens if the unamplified signal and the amplified signal are equal in intensity?
They two signals combine and are perceived as one
What happens if the direct signal is substantially louder than the unamplified signal?
It will mask it
What is a potential vent issue?
The final output may be altered by the direct signal moving inward and the amplified signal moving outward being in-phase or out-of-phase
Cancel or double
What is the culprit of the in-phase/out-of-phase issue with vents?
Standing waves
What creates a feedback loop?
When high frequency output energy increases and escapes canal through the vent
Creates feedback
How much gain does an occluded mold allow?
40 dB of gain at 3 kHz
Supports audibility to 80 dB HL
How much gain does a 3 mm vent allow?
30 dB of gain at 3 kHz
Supports audibility to 60 dB HL
How much gain does an open dome allow?
25 dB of gain at 3 kHz
Supports audibility to 50 dB HL
Is vent size inversely related to high frequency output?
Yes
What is a parallel vent?
The sound bore and the vent travel through the ear piece side-by-side without intersecting
What is an angle vent?
The vent intersects with the sound bore as close as possible to the tip of the canal
Decreases high freq output and increases potential for feedback
Used as a last resort
What is a half external vent and a trench vent?
A channel from the tip of the canal to halfway down and then transitions to an internal vent
Behave similarly to parallel vents
What is the only real way to know the vent effect?
Measure it during real ear
What vent size is recommended for a 50-60 dB loss at 500 Hz?
0.5 to no vent
What vent size is recommended for a 40-49 dB loss at 500 Hz?
1-2 mm
What vent size is recommended for a 30-39 dB loss at 500 Hz?
2-3 mm or power dome
What vent size is recommended for a 20-29 dB loss at 500 Hz?
3-3.5 mm or closed dome
What vent size is recommended for 20 dB threshold to 1.5 kHz?
Open dome
What is a pressure vent?
Allows the release of pressure resulting from snug earmolds
0.5 mm
Does not release a significant amount of low frequency energy
Can select-a-vents significantly change the acoustic mass?
No
Can select-a-vents significantly change the vent effect?
May not
