Hearing assistance devices include a variety of devices such as assistive listening devices, cochlear implants and hearing aids. Hearing aids are useful in improving the hearing and speech comprehension of people who have hearing loss by selectively amplifying certain frequencies according to the hearing loss of the subject. A hearing aid typically has three basic parts; a microphone, an amplifier and a speaker. The microphone receives sound (acoustic signal) and converts it to an electrical signal and sends it to the amplifier. The amplifier increases the power of the signal, in proportion to the hearing loss, and then sends it to the ear through the speaker. Cochlear devices may employ electrodes to transmit sound to the patient.
Undesired sounds such as noise, feedback and the user's own voice may also be amplified, which can result in decreased sound quality and benefit for the user. It is undesirable for the user to hear his or her own voice amplified. Further, if the user is using an ear mold with little or no venting, he or she will experience an occlusion effect where his or her own voice sounds hollow (“talking in a barrel”). Thirdly, if the hearing aid has a noise reduction/environment classification algorithm, the user's own voice can be wrongly detected as desired speech.
Typical hearing aid microphones have difficulties properly detecting a wearer's own voice. Problems include poor signal to (ambient) noise ratio, poor speech intelligibility, and ingress of foreign debris into the microphone. Prior solutions to this problem include: (1) the telecom industry typically uses a directional microphone system either in the housing (on the lateral side of an in-ear device) or on a boom, thereby positioning the microphones closer to the mouth. However, these directional microphones are susceptible to outside ambient noise, thereby degrading SNR and speech intelligibility, and are susceptible to foreign debris; (2) Kruger (U.S. Pat. No. 5,692,059) entitled Two active element in-the-ear microphone system combined the outputs of a dedicated airborne transducer together with a dedicated non-airborne transducer to produce a composite own-voice signal. Each transducer sensed a different frequency portion of the user's own-voice to produce the composite output. A piezoelectric accelerometer was the preferred non-airborne transducer. However, Kruger requires two different transducers: an airborne transducer and a non-airborne transducer. One transducer is dedicated to high frequency fricatives and the other is dedicated to low frequencies. A separate transducer dedicated to low frequencies, though it may give better sound quality, is superfluous for speech intelligibility in that low frequencies are not crucial for such as shown in FIG. 10; (3) Darbut (U.S. Patent Application No. 2007/0127757) entitled Behind-the-ear auditory device used an acoustic canal pad comprised of a flexible membrane and rigid base such that acoustic signals were amplified and routed to a microphone (paragraph 0130). Furthermore, the single-port (omni) microphone is coupled to this rigid base via “dampening elements whose internal prongs are offset from the external prongs, thereby isolating the microphone from vibration” (paraphrased from paragraphs 0072-3). However, Darbut employs an “at least partially in-ear element” which consists of a standard housing with an ‘acoustic pickup cushion pillow’ or ‘acoustic canal pad’ as described in 1(c) above. It functions as a “stethoscope-like” device; specifically, it provides acoustical amplification from vibrations of the cartilaginous portion of the ear canal. Since a standard housing is used for the in-ear element, a second pad is positioned opposite the acoustic canal pad in order to snugly position the standard housing against the cartilaginous portion of the ear canal and thereby allow the stethoscope-like device to amplify properly; (4) Platz (U.S. Patent Application No. 2011/0243385) entitled System for picking-up a user's voice used a standard ‘one-size-fits-all’ earmold to be worn at least partly in a user's ear canal together with an elongated, C-shaped retention element attached to the shell of the earmold and brought into engagement of a user's concha by manual plastic deformation by the user, thereby providing the necessary contact force between an ear microphone (i.e., a microphone oriented acoustically inwardly towards the user's ear canal and adapted for picking up the user's voice via bone conduction from the skull) and the ear canal wall. In a different embodiment, a first ‘ear’ microphone oriented acoustically inward towards the user's ear canal and a second ‘ambient’ microphone oriented outwardly towards the environment, with a sound port terminating at the outer end of the earmold, is used. Digital signal processing of the two microphone signals is performed to achieve Blind Source Separation (BSS) of the signals and thus eliminate the need of “bone-conduction microphones which would cause discomfort to the user” (paragraph 0032). However, in Platz the ear-canal microphone will not function properly without the C-shaped retention element engaged within a user's concha. In addition, this bone conduction microphone “would cause discomfort to the user” (described in paragraph 0032). As shown, the ear-canal bone conduction microphone depicted in the FIG. 3 of Platz has a separate protrusion from the earmold housing, presumably the cause of user discomfort.
Thus, there is a need in the art for an improved method and apparatus for own-voice sensing in hearing assistance devices.