RIC assembly with thuras tube

A hearing aid assembly comprising a receiver comprising a front chamber and a back chamber being acoustically coupled to respective front and back chamber openings, and acoustical guiding means for guiding air from at least one of the front and back chamber openings to an air mixing zone for mixing air from the front and back chamber openings. The mixing of air from the front and back chambers enhances the low-frequency response of the hearing aid assembly.

FIELD OF THE INVENTION

The present invention relates to a hearing aid assembly. In particular, the present invention relates to a so-called receiver in the canal (RIC) hearing aid assembly having an enhanced low-frequency performance.

BACKGROUND OF THE INVENTION

It is well-known that traditional receivers applying domes with holes exhibit a significantly reduced low-frequency response due to the low frequency filtering characteristics of the holes in the dome.

A direct comparison between frequency responses of a closed dome and an open dome is shown inFIG. 1. It is evident that the sound pressure level (SPL) of the closed dome is significantly higher that the SPL of the open dome in the frequency range from 100 Hz to 2 kHz.

In view of the above-mentioned lack of low-frequency performance it may be seen as an object of embodiments of the present invention to provide a receiver arrangement for a hearing aid assembly, said receiver arrangement enhancing the low-frequency response for receivers applying an open dome arrangement.

SUMMARY OF INVENTION

The above-mentioned object is complied with by providing, in a first aspect, a hearing aid assembly comprisinga receiver comprising a front chamber and a back chamber being acoustically coupled to respective front and back chamber openings, andacoustical guiding means for guiding air from at least one of the front and back chamber openings to an air mixing zone for mixing air from the front and back chamber openings.

It is an advantage of the present invention that the suggested mixing of air from the front and back chambers in the air mixing zone increases the low-frequency performance of the hearing aid assembly. In case of a full range receiver, the frequency performance is increased for the low frequencies of the full range. In case of a tweeter i.e. high frequency receiver, the frequency performance is increased for the low frequencies of the high-frequency range.

The hearing aid assembly may form part of a RIC hearing aid where the above-mentioned assembly is adapted to be positioned in the ear canal whereas other parts of the RIC hearing aid, such as battery, microphone etc., may be positioned outside the ear canal.

The receiver may be a balanced armature-type receiver. However, other types of receivers having front and back chambers may be applicable as well.

The air mixing zone may form part of an air mixing chamber which may be acoustically coupled to a sound outlet of the assembly. The sound outlet of the hearing air assembly may comprise a dome.

In an embodiment of the invention the front chamber opening may form part of the air mixing zone. The acoustical guiding means may thus be coupled to the back chamber opening so as to guide air from the back chamber opening to the air mixing zone. The air mixing zone may be in direct acoustical contact with the dome of the sound outlet of the hearing aid assembly in that the dome may form part of the boundaries of the air mixing zone.

When air from the back chamber opening arrives at the air mixing zone it has been phase-shifted and delayed compared to the air from the front chamber opening. The introduced phase-shift is caused by the fact that air from the front chamber opening is generated when the receiver membrane moves in one direction, whereas air from the back chamber opening is generated when the receiver membrane moves in the opposite direction.

The acoustical guiding means may comprise a tube, such as a flexible duct, having a predetermined length and a predetermined inner diameter. The tube may show a low-pass frequency behaviour because high-frequency components (above 3 kHz) are typically damped by the tube geometry.

Various predetermined lengths and inner diameters have been tested in order to optimise the low-frequency response of the hearing aid assembly. Thus, the length of the tube may be selected in accordance with the relevant frequencies in order to utilize the acoustical resonance of the tube.

As a result of the tests the predetermined length and the predetermined inner diameter of the tube may typically fall within the ranges 20-100 mm, such as 3-80 mm and 0.5-1.0 mm, such as 0.25-0.75 mm, respectively. However, other tube dimensions may be applicable as well.

At least one electrical connector adapted to connect the receiver to exterior electrical components of the hearing aid assembly may be provided. Such exterior electrical components may involve batteries, amplifiers, microphones etc.

It may be advantageous from a space saving perspective to position one or more electrical wires interconnecting the receiver and the at least one electrical connector at least partly within the acoustical guiding means. In this way vulnerable free-hanging electrical wires between the receiver and the electrical connector can be avoided.

DETAILED DESCRIPTION OF THE INVENTION

In its most general aspect the present invention relates to a hearing aid assembly, such as a RIC hearing aid assembly, where air from a receiver's back chamber is mixed with air from the receiver's front chamber. This mixing of air from the two chambers enhances the low-frequency response of the hearing air assembly significantly. An increase of around 6 dB in SPL may be achieved; or even more. Acoustical guiding means, such as a flexible tube, is provided for guiding air from the back chamber to a mixing zone in the form of a chamber where also air from the front chamber is present. The mixed air drives a sound outlet dome of the overall hearing aid assembly. The length and the diameter of the acoustical guiding means influence the low-frequency performance of the hearing aid assembly.

Referring now toFIG. 2a hearing aid assembly200according to the present invention is depicted. The assembly comprises a body201and a sound outlet dome202attached thereto. The body houses a receiver203having a front chamber204and a back chamber205. Pressurized air may escape from the two chambers via respective sound openings206(front chamber) and207(back chamber). An acoustical seal208is provided between the receiver and the body201in order to avoid uncontrolled mixing of air from the two chambers. The receiver is electrically coupled to the connector209via electrical wires210. The connector209ensures that the receiver can be electrically connected to exterior parts, such as a behind-the-ear (BTE) part, of the hearing aid.

A tube section211is provided between the body201and the connector209. This tube section211forms an acoustical channel where pressurized air from the back chamber opening207is allowed to enter and propagate. An additional tube section212and a passage214are provided for leading pressurized air to a mixing zone near the front chamber opening206so that air from the front and back chamber openings206,207are mixing in order to enhance the low-frequency response of the hearing aid assembly200. The air arriving from the back chamber opening207is in phase when it blends with air leaving the front chamber opening206.

When air from the back chamber opening207is guided to the mixing zone behind the sound outlet dome202the low-frequency performance of the assembly is highly improved in that the SPL in the low-frequency range, typically below 2 kHz, is increased significantly.

The high-frequency performance of the hearing aid assembly is primarily dominated by sound escaping from the front chamber opening of the receiver. The tube sections211,212act as a low-pass filter having a cut-off frequency of around 3 kHz. Thus, essentially no high-frequency components are allowed to pass through the tube sections211,212.

Thus, it is advantageous that the increased low-frequency performance caused by the air from the back chamber opening does not influence the average high-frequency performance of the assembly in any particular way.

The receiver203shown inFIG. 2is a balanced armature-type receiver. However, other types of receivers having front and back chambers may be applicable as well.

A three-dimensional illustration of the RiC part of a hearing aid assembly is shown inFIG. 3. The hearing aid assembly comprises a body301housing the receiver (not shown) and the connector304interconnected by the tubes302and303. The tube302is leading air from the back chamber of the receiver to the air mixing chamber behind the sound outlet305. The tube303, which also serves as an air guiding passage, contains electrical wires interconnecting the receiver (not shown) and the connector304.

FIG. 4shows a comparison of the SPL from a receiver having an open back chamber and a similar receiver being equipped with a tube which in the following is denoted a thuras tube. As seen inFIG. 4the thuras tube increases the SPL in the frequency range from around 300 Hz to around 2 kHz. The thuras tube used in connection with the results presented inFIG. 4has a length of 90 mm and an inner diameter of 0.75 mm.

FIG. 5ashows the achievable SPL for various lengths of the thuras tubes. The tendency is clear in that the low-frequency response increases with increasing length of the thuras tube. Also, maximum SPL seems to shift towards lower frequencies with increasing length.

FIG. 5bshows the achievable SPL for various tube diameters. As seen inFIG. 5b, an optimal low-frequency performance seems to exist for tube diameters of around 0.75 mm where the low-frequency response is maximal in terms of achievable SPL, at least in the frequency range 300 Hz to around 2 kHz.

FIG. 6illustrates that the acoustical performance of the hearing aid assembly is essentially not influenced by the presence of electrical wires being arranged in at least part of the thuras tubes. For comparison, the frequency response of a traditional receiver having no thuras tube is shown as well. As seen inFIG. 6the traditional receiver shows a lower SPL (up to around 6-7 dB) in the frequency range 250 Hz to around 2 kHz.

Another embodiment of the invention is shown inFIG. 7. This shows a RiC hearing aid assembly600comprising a low-frequency receiver614and a high-frequency receiver604, e.g. applicable as a woofer—tweeter receiver combination for HiFi purposes. The woofer i.e. the low-frequency receiver614outputs the low frequency range, the tweeter i.e. the high-frequency receiver603outputs the high-frequency range of the output. The woofer is positioned in the BTE part615of the hearing aid, the tweeter is positioned in the RiC part616of the hearing aid. The sound of both receivers603,614is outputted through the sound outlet dome602.

In such a distributed system the tweeter has a peak at around 5 kHz, instead at 3 kHz common for full range receivers which is desired as it approaches the natural resonance frequency associated with the human ear. To reduce the cross-over effects associated with the split of the frequency spectra of the respective receivers, the thuras tube can be optimised to provide an increase of the low part of the high-frequency spectrum, particularly at 3 kHz. Accordingly, the the full range output of the hearing aid shows an improvement due to the frequency performance increase at 3 kHz.