Venting, Sound-Bore Modifications

Earpiece Sound-Bore Guidelines

With the advent of digital hearing instruments and signal-processing technology, a section on basic earpiece acoustics may soon become passé. For now, however, there are three common ways to control the amplified signal of a hearing instrument once the signal leaves the receiver; venting, dampers, and sound-bore modifications.

Venting typically affects frequencies below 750 Hz. In general, the larger the vent, the more low-frequency energy is "bled off." By using different vent diameters, varying amounts of low-frequency amplification can be reduced. Earpiece venting can range from totally open or non-occluding styles to very precise and interchangeable venting via a vent control insert such as a mini vent plug (MVP).

Open earpiece fittings are earpieces with very large vents. These types of earpieces can be quite effective for hearing losses that do not require low-frequency amplification. They allow the patient to perceive low-pitched sounds naturally (through the open vent), while using an instrument for high-frequency amplification. Reduction or elimination of the occlusion effect is an added benefit for the patient.

Damping primarily affects frequencies between 1 and 3 kHz due to the effect the damper has on the resonant peaks of the hearing instrument. As the name suggests, the damper dampens or smooths out the frequency response of a hearing instrument. As a result, the sound quality of the hearing instrument is much more natural, with feedback less likely. Dampers can be fit to the ear hook, the earpiece tubing or the sound bore of the earpiece. The location determines the amount of smoothing the damper will achieve. The closer the damper is to the end of the signal chain, the greater its effect on smoothing response peaks.

The size and shape of the sound bore can also control the frequency response of the earpiece/hearing instrument combination. Changes in bore diameter can affect frequencies at 1.5 kHz and above. Larger sound-bore diameters and tubing can result in a 3 to 5 dB gain above 1.5 kHz, such as the case with a half tubed earpiece. Additional high-frequency gain can be realized by specifying a Libby Horn tube. Smaller tube diameters can also reduce high-frequency gain, as needed for reverse-slope hearing losses.

Proper use of these basic acoustic principles can improve the performance of even the most sophisticated digital instrument.

 Sound-Bore Glossary

Large bore (LB) (horn effect)
A 4 to 5 mm bore at the end of the canal that mimics the horn effect and helps increase high frequencies.

Small bore (SB) (reverse horn effect)
A 1mm bore that helps boost perceived low frequencies by reducing high frequencies.

Open bore (OB)
Commonly used with gently sloping, high-frequency losses. The canal is cut short and "hollowed." An example is Westone's Style No.10 Earpiece.

Fishmouth (FM) (bell bore)
Not a true acoustic modification, but rather a beveled cut in the end of the sound bore that acts as a cerumen trap.

Venting Glossary

Angle vent (AV)
The vent intersects the sound bore between the end of the tubing and the end of the earpiece canal.

Half external vent
A channel from the canal tip to the aperture that transitions to an internal vent. Used when drainage or discharge from the ear is a problem.

Parallel vent (PV)*
The sound bore and the vent travel through the earpiece side-by-side and do not intersect.

Mini vent plugs (MVP)
Normally drilled with a 3 mm diameter bore. MVPs come with each of the following vent sizes: #(2.5 mm), #2 (2 mm), #3 (1.5 mm), #4 (mm), #5 (0.8mm). Includes one solid plug.


*We always drill vents parallel as a default if no vent configuration is specified. If the physical size of the earpiece or acoustic requirements prevent us from using a parallel vent, we will install an angle vent.