Hearing aid with enhanced vent

A hearing aid with a microphone for receiving acoustic signals and converting them to electrical signals, electronic circuitry for processing the electrical signals, and a speaker for converting the processed electrical signals into acoustic signals, has a shell that encases at least portions of the microphone, the electronic circuitry, and the speaker, the shell further encasing an inside volume. The hearing aid further has a vent that provides an opening between the inside volume and a region external to the hearing aid. A flexible membrane is provided that covers an opening of the vent and an acoustic resistor that contacts the flexible membrane. The membrane helps prevent wax fumes from entering the inside volume, and the acoustic resistor helps to reduce distortion in the frequency response of the hearing aid.

BACKGROUND

The present invention relates to a hearing aid, and specifically to a hearing aid having an enhanced vent that produces sound having beneficial characteristics.

A custom hearing aid typically includes a vent. The main purpose of the vent is to reduce the “occlusion” effect, which is defined as an unpleasant sensation related to a loud sound of the hearing aid user's voice. The occlusion sound is generated due to vibrations of the ear canal tissues that are generated, e.g., when the wearer speaks.

The intensity of the occlusion sound is drastically increased when a hearing aid user inserts the aid into the ear. This is because the hearing aid blocks the ear canal, thereby forming a closed volume around the ear drum. When this happens, the sound pressure, caused by vibrations of the canal tissues, increases to levels that make it very annoying to the hearing aid users.

In conventional hearing aid designs, a conventional vent forms a passage for the ear from the closed volume near the ear drum to the outside space, thereby allowing a reduction of the occlusion effect.FIG. 3illustrates the frequency response of a hearing aid with a conventional vent design.

One negative effect of such a vent, however, is to increase the occurrence of an acoustic feedback by letting the amplified sound pressure from the ear canal enter into the microphone, thereby creating a feedback loop. A hearing aid with a vent has a limited stable gain that is determined by the vent cross-section area, vent length, and the distance between the vent opening and the microphone inlet.

The prior art International patent publication WO 92/21218 (“Gauthier”) illustrates a known hearing aid design (seeFIG. 1), showing a microphone10, receiver (speaker)12, various electrical components14,16,18, and20mounted on a printed circuit board22, a battery housed in a battery compartment24, and wires26running from the printed circuit board22to the speaker12. The speaker has a sound conducting tube28that opens to the ear canal of the user.

Gauthier discloses a vent construction that allows an increase in the stable gain of a hearing aid. The hearing aid has a housing30that has an air vent passage32extending along the length of the housing and conducts sound from the ear canal to outside of the ear. Gauthier's modified vent (referred to as a “tuned passage”)42has an opening from the vent32into the inside volume38of the hearing aid.

However, the vent construction of Gauthier has the following disadvantages:1. Due to the resonance effects of the Helmholtz resonator that is formed by the opening42and the inside volume38, the frequency response of the hearing aid becomes strongly distorted. In addition to the expected reduction of the gain at low frequencies (due to leaks of sound energy through the vent), the response developed is illustrated inFIG. 4. Also the increased sound pressure inside the shell38leaks into the microphone10inlet via the gaps in the battery door, creating another feedback path and causing peaks in the response curve near the 1-3 kHz frequency range, as is illustrated inFIG. 4.2. The wax fumes go through the opening42into the inside of the hearing aid38and create wax deposits causing corrosion and a consequential malfunction of the electronic parts of the hearing aid.

SUMMARY

The invention is directed to a hearing aid, comprising, according to various embodiments: a microphone for receiving acoustic signals and converting them to electrical signals; electronic circuitry for processing the electrical signals; a speaker for converting the processed electrical signals into acoustic signals; a shell that encases at least portions of the microphone, the electronic circuitry, and the speaker, the shell further encasing an inside volume; a vent that provides an opening between the inside volume and a region external to the hearing aid; a flexible membrane that covers an opening of the vent; and an acoustic resistor that covers the flexible membrane on the side of hearing aid components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2illustrates an embodiment of the present inventive hearing aid design. As with the design of Gauthier,FIG. 2shows a microphone10, speaker12, various electrical components14,16,18, and20mounted on a printed circuit board22, a battery housed in a battery compartment24, and wires26running from the printed circuit board22to the speaker12. The speaker has a sound conducting tube28that opens to the ear canal of the user.

According to this embodiment, however, the enhanced vent32includes an opening in the vent42that is covered with a small flexible membrane44. This membrane44allows the sound from the vent42to go into the inside volume38of the hearing aid while protecting it from the wax fumes.

The membrane44used may be of a type described in U.S. Patent Publication No. 2005/0018866, herein incorporated by reference, and behaves like a very thin non-stretched film that re-radiates sound pressure on one side to the other side without substantial losses.

The opening also may include an acoustic resistor46in the form of, e.g., a stretched tight cloth, a tight metal mesh, etc, that is positioned between the membrane44and the inside volume38of the hearing aid. The acoustic resistor46allows the hearing aid to obtain a smooth response of the vented hearing aid and to achieve higher stable gain and better occlusion reduction, as illustrated in the frequency response curve shown inFIG. 5.

By way of example, in a preferred embodiment, the acoustic resister for the system described herein has a resistance in the range of 50-200 acoustic ohms, with a practical membrane having a diameter of 3 mm. Such membrane type devices for the protection of receivers from ear wax are disclosed in U.S. Patent Publication 2005/0018866. A typical range of vent diameters is within 1-3 mm.