Hearing aid with acoustical frequency response modification

A hearing aid for individuals with a loss of sensitivity to the higher frequencies acoustically attenuates the lower frequencies by providing a sound reproducer coupled to a sound delivering conduit provided with an aperture of prescribed size coupled to a cavity which surrounds the sound reproducer.

This innovation relates to a hearing aid for persons who are hard of 
hearing, comprising a sound receiver, amplifier, and sound reproducer, to 
which a conduit for delivering sound is connected, and it is an object of 
the invention to facilitate the adaptation of the appliance to the hearing 
characteristics of the persons who are hard of hearing. 
Persons who are hard of hearing lose first the ability to hear the higher 
sound frequencies. For this reason the adaptation resides, as a rule, in 
an attenuation of the lower frequencies (generally the frequencies in the 
range of 0.5 to 2 kHz) so that the entire frequency range can be amplified 
whereas the lower frequencies are not amplified with the same gain as the 
higher frequencies. 
In accordance with the innovation this adaptation is accomplished by an 
acoustic loading of the sound-transmitting path between the sound 
reproducer of the hearing aid and the ear of the person who is hard of 
hearing. In accordance with the innovation this acoustic loading is 
accomplished in that one or more openings disposed within the housing lead 
from the interior of the conduit to a cavity which surrounds the sound 
reproducer. 
In the simplest embodiment, there is at least one opening consisting of a 
bore through the wall of the conduit. In another suitable arrangement, at 
least one opening is formed in a bushing, which is inserted in the wall of 
the conduit.

The housing of the hearing aid comprises a wall 1, which encloses a cavity 
3 which contains the sound reproducer 2 of the appliance. A flexible 
tubing 5 is connected to the sound reproducer within the housing and 
extends outwardly through a wall of the housing. A bushing 4 is inserted 
in the wall of the tubing within the housing. The opening in the bushing 4 
leads from the interior of the flexible tubing into the cavity 3. The 
bushing 4 may have a plurality of openings or may consist of a tube, which 
is connected between the sound reproducer 2 and the flexible tubing 5 and 
formed with one or more openings. 
The sound pressure generated in the sound reproducer under electrical 
control is conducted through the flexible tubing 5, which is provided with 
the bushing 4, to an artificial ear, not shown, which defines a cavity of 
about 2 cm.sup.3, in which a condenser microphone is inserted. The bushing 
4 provided with one or more opening constitutes an acoustic load, which 
attenuates the transmission of sound at lower frequencies. 
The equivalent circuit diagram of the system for transmitting sound at 
lower frequency is shown in FIG. 3. Pi and Po designate, respectively, the 
sound pressure generated by the sound reproducer and the sound pressure 
received by the artificial ear, the equivalent parameters of which are 
designated Z and Ck. 
The equivalent parameters of the cavity 3 and of the flexible tubing 5, 
which is provided with the opening according to the innovation, of the 
hearing aid are designated CG, R, L and C. The opening or openings in the 
wall of the flexible tubing are so dimensioned that C and R constitute a 
damped resonant system, which prevents at the same time an acoustic 
feedback between the sound receiver and the sound reproducer. When the 
hearing frequency response of a person who is hard of hearing is known, 
the size of the opening or openings provided according to the invention 
may be adapted and checked by means of the artificial ear.