Sistems of assisted listening
We are going to explain three systems of assisted listening that use modulated frequency waves, FM. These systems can in some cases communicate an emitter with several receivers, for example an event. And in other cases an emitter to a single receiver, as would be a class for a student.
This system allows a single transmitter such as an audio table in an assembly hall, portable microphones, etc. can broadcast for several receivers.
Transmitter (one): High power portable stationary FM emitter
It emits an FM signal. This signal is limited to a few tens of meters. The following image shows a station of the brand Listen. We can connect to this station, any audio signal through an audio mediate un 3.5 mm jack cable, such as the audio output from a mixer in an auditorium or the receiver of a wireless microphone system.
We will choose an FM channel from among the eight predefined by the manufacturer to emit the signal. We can also regulate the emission power to have a greater or shorter range depending on the characteristics of the room.
Receiver (several): Portable FM receiver
We can use headphones or induction loop connected to this channel. The hearing will be perfect, with clear sound and without noise, and regardless of the distance to which we are. The following image shows a portable FM Receiver of the brand LISTEN. The receivers must be connected to the channel selected by the emitter that is emitting.
We can listen to the received sound by connecting the 3.5 mm jack port to some headphones or an induction loop. In the receiver we can increase or reduce the volume of audio to adapt it to our listening needs.
Headphones and induction loop
We can connect some headphones, like the ones shown in the following image:
But also, we can connect an induction loop like the one shown in the following image. This induction loop is also connected to the 3.5 mm jack port of the FM receiver and the user places it around the neck, hence the name "loop". This cable located around the neck creates a magnetic field that is induced by cochlear implants or hearing aids of people with hearing impairment and transform that signal into high quality sound.
The hearing aids must be analogue and have the T-telecoil position in order to induce these magnetic fields. In the case of digital hearing aids we will not be able to access this feature.
At the University of Alicante we have a loop with an emitter for use in conference halls, such as those used in the Conference on Accessible Technologies and Support Products of the University of Alican te, and 4 receivers with 4 normal headphones and 4 loops of induction.
It is a similar system to the previous one, but in this case, the communication is individual; there is only one emitter emitting and one receiver receiving on the FM channel.
At the UA we offer a packet of FM transmitter and receiver to students with hearing disabilities. These students at the beginning of the class make it easy for the teacher to connect, the transmitter with a lapel microphone and it is placed near the mouth so that the sound has the least noise and the highest possible quality.
Transmitter (one): Emitter with microphone for lapel
The following image shows an FM transmitter with a lapel microphone and an FM receiver connected to a headset.
Receiver (one): FM receiver connected to headphones or induction loop
The student usually sits in class with their receiver and according to their needs, connects a headset or an induction loop to hear the teacher's voice clearly.
This system simulates the operation of a cochlear implant or the T position of an analogue hearing aid. This receiver is capable of inducing the existing magnetic field in fixed magnetic loops made by work in rooms and will allow to hear that signal with headphones.
The following picture shows a telecoil receiver with a headset connected to it.