Today's modern classroom is a noisy place. For a student with a hearing loss the classroom is actually a hostile or toxic listening environment from which they receive very limited acoustical instruction. This is do partly because of the way we build today's classrooms (hard surface walls, large glass windows, tile or concrete floors, etc. And partly do to the laws of physics for acoustical properties which states that every time we double the distance between the speaker and listener we drop or lose 6 decibels (dB) in volume. The average adult male teacher speaks at 65 dB SPL and the average adult female teacher speaks at 62 dB SPL at a distance of 3-feet from their lips. The average noise floor in a classroom is between 56 dB SPL and 60 dB SPL. The first row of seats in a classroom is about 6-8 feet from the teacher and the last row is approximately 24-30 feet from the teacher. Using the shorter distances and computing the voice volume for a female teacher we then have at the first row the average a voice volume of 56 dB SPL and at the last row a voice volume of 44 dB SPL. For the best understanding a normal hearing person needs +10 dB Signal to Noise Ratio (SNR). Below this point they can function but are working very hard to follow what is being said. For a student with a mild to moderate hearing loss the ratio should be +20 dB SNR. At 6 feet we have a ratio of 56 dB SPL for the teacher's voice with a noise floor of 56 dB SPL giving us a 0 SNR and at 24 feet we have a -12 dB SNR. Even normal hearing students, in the back half of a classroom struggle to understand what the teacher is saying. To overcome this problem we look toward an Roger system for hard of hearing students and soundfield systems to help normal hearing students.
The Purpose of an Roger System
In the past we have used FM systems to meet the special needs of students in the classroom but with the advent of the Roger system which uses new and improved digital techniques to improve clarity for the student. The Roger system is uniquely designed to capture the teacher's voice close to their lips, 1-18 inches, before the room noise can blend with the voice and move the teacher's voice electronically to hard of hearing student's hearing aid were it is then amplified in such a way that the student will receive maximum benefit from what is said by the teacher. This lets us work around the laws of physics and the inverse square law for acoustics. We now provide the +20 dB SNR, needed by a hard of hearing student, to follow an oral discussion without being totally exhausted before half the day is over.
The Roger System
The Roger system is composed of two basic parts, the transmitter and the receiver, plus a method of coupling the receiver to the students ear, hearing aid or cochlear implant. Since most hard of hearing students wear hearing aids or a cochlear implant (CI) the coupling is generally done through a form of magnetic induction or by direct coupling, called Direct Audio Input or DAI.
Important Note about Telecoils vs. DAI
As explained earlier, a telecoil, also called a T-coil or Induction coil, is designed to pickup a fluxing magnetic field, generated by an induction loop or neckloop, and feed the signal into a person's hearing aid or CI. The difference between an induction loop and a neckloop is the induction loop is designed to cover an area or classroom while the neckloop does the same thing on a more personal level, generating the field just around the head and neck of the person.
Roger vs. FM Products