Telephone handset attachment for use in-the-ear hearing aids

An attachment for a telephone handset used by users of in-the-ear hearing aids including a cup shaped member which acoustically couples the handset to the ear and serves to cancel feedback between the hearing aid receiver and microphone.

This invention relates generally to a telephone handset attachment for use 
by individuals who use in-the-ear hearing aids. 
Most all in-the-ear (ITE) hearing aid users have a problem when using any 
type of telephone on the ear in which they wear the ITE hearing aid. When 
the telephone receiver is placed on the ear, an acoustic cavity is formed 
with the walls of the cavity defined by the ear and the face of the 
telephone handset receiver. This acoustic cavity couples the hearing aid 
receiver output to the hearing aid microphone to provide acoustic 
feedback. This causes the hearing aid to go into acoustic oscillations at 
a frequency determined by the size of the cavity, primarily in the 
frequency range between 3,000-5,000 Hz, with harmonics at lower 
frequencies. During this oscillation (feedback) no sound level below the 
sound level of the acoustic feedback is amplified by the hearing aid. This 
makes it virtually impossible for the ITE hearing aid user to utilize the 
telephone on the ear where amplification at frequencies where hearing is 
impaired is needed. 
Recently hearing aid circuits have been developed which include acoustic 
feedback control circuits. These circuits are mainly an external 
adjustment of the amplifier gain in the frequency range where feedback 
occur. These feedback circuits prevent the ITE hearing aid from going into 
acoustic feedback when normally worn and used. However, when used in 
connection with the telephone it does not prevent the hearing aid from 
creating the described acoustic feedback and oscillation. 
It is an object of the present invention to provide a telephone attachment 
which introduces an acoustic cavity between the telephone receiver and the 
in-the-ear hearing aid to cancel the acoustic feedback between the hearing 
aid microphone and receiver. 
The foregoing and other objects as achieved by an attachment which 
comprises a cup shaped housing having an open end adapted to fit over the 
ear of the user and a closed end including an opening. Means are provided 
for acoustically coupling the telephone receiver to the housing to permit 
sound to enter through the opening and means are also provided for 
attaching the housing to the handset whereby the telephone receiver can be 
coupled to the ear via the cup shaped housing which acts as an acoustic 
cavity resonating at the feedback frequency and acting to cancel feedback 
from the hearing aid receiver to the hearing aid microphone.

The attachment comprises an ear cavity shell or cup 11 made of any suitable 
material, preferably plastic, which includes a suitable compliant acoustic 
sealing material 12 for sealing the cup to the telephone receiver and an 
opening 13 providing acoustic communication between the telephone receiver 
and the interior of the cup. Preferably one or more pieces of acoustic 
foam 14 are held in the cup. A strap 16 has one end attached to the cup 
and its other end adapted to cooperate with the VelCro material 17 on the 
other side of the cup for attaching the handset coupler to the telephone 
handset 18 as shown particularly in FIG. 2. 
The cavity shell 11 is designed and "tuned" so that it resonates in the 
frequency range in which the ITE hearing aid feedback occurs. The foam is 
placed in and fills up the shell cavity and its purpose is mainly to 
attenuate the harmonics created by the hearing aid's lower frequencies. 
The shell cavity amplifies at the ITE hearing aid's feedback frequency and 
the amplified acoustic waves are directed towards the ear, they interfere 
with the feedback between the microphone and receiver and they form a 
standing wave. This cancels out the feedback signals. This enables 
amplification of the incoming signal from the handset enabling the user to 
hear the telephone converstion. 
Thus, there has been provided a telephone attachment which enables a user 
of an in-the-ear hearing aid to use a telephone.