By:     Melissa Clark, Au.D., CCC-A,              melissa-clark-photo-small-square

     DHH Consultant at Nine East Network







One of our jobs as Consultants for the Deaf and Hard of Hearing is to help students listen and learn in the classroom.


Classroom environments are typically noisy, and noise can make it difficult for any child to access auditory information.


Classroom noise can include any auditory disturbance that interferes with what a person wants and/or needs to hear.  This includes noise from outside of the building, noise from within the building, and noise from within the classroom.


Auditory information is defined as any information that is intended to be heard. This often includes teacher instruction, peer comments and questions, information from digital media, and overhead announcements.


A signal to noise ratio (SNR), is the comparison of the measured loudness of the auditory information (signal) to the loudness of the noise. SNR is a significant factor in determining the ability to understand speech.


Distance between the listener and speaker needs to be considered when discussing loudness of a signal, because the level of a signal’s loudness decreases over distance.


Also, distance needs to be considered when discussing the effectiveness of hearing aid microphones.  Hearing aid microphones are most effective for signals and noise within 6 feet of the microphone.


So, how can we help students overcome the challenges of listening in noise and at a distance?  


We have found that using appropriate communication and listening strategies such as getting closer, moving away from noise, and watching the speaker can reduce the challenges of listening in a difficult situation.


Additionally, using hearing assistive technology can also make listening easier for students. We often recommend hearing assistive technology in the classroom to overcome these challenges.


Hearing assistive technology is commonly found in classrooms, and this is especially true for classrooms that have students with diagnosed hearing loss or (Central) Auditory Processing Disorder.


Hearing assistive technology helps listeners access communication by improving the signal to noise ratio, which mitigates the effects of listening in noise, at a distance, and in reverberation.


Many classrooms in Vermont are using hearing assistive technology – often referred to as an FM (frequency modulated) or DM (digital modulated) system.


FM and DM systems are comprised of a teacher-worn transmitter and a receiver. The transmitter is a microphone that wirelessly transmits a signal (teacher’s voice, digital audio) to a receiver. The receiver may be worn at ear level by the student, or can be a classroom soundfield speaker.


Here is an example of a hearing aid set up for FM:




The most important difference between FM and DM systems is that DM systems have advanced dynamic behavior leading to improved speech recognition in noise when compared to FM systems.


A Phonak Field Study News edition, “Roger for Hearing Instruments” reports results from a study by Dr. Linda Thibodeau (2013) that revealed there was a 35% to 55% improvement in speech recognition in noise when compared to dynamic and traditional FM systems.


When a decision has been made for a school to order hearing assistive hearing technology, then the school will need to ensure that the system is verified by an audiologist.  Verification ensures that the equipment is functioning properly and that there is not too much or too little gain.


Verification Guidelines for FM equipment have been published by the American Speech and Hearing Association and by the American Academy of Audiology.  FM systems need to be verified anytime a receiver or transmitter is replaced. Also, it is recommended that verification happen annually.


DM equipment verification




Pictured on the right is DM Equipment Verification.


A hearing aid, with the Roger receiver attached, is connected to the test system and placed inside the test box. The screen shows the measured output from the hearing aid and compares the output to the DM signal.





Currently, schools in Vermont can have FM/DM equipment verified at Dartmouth-Hitchcock Medical Center, University of Vermont, and at Rutland Regional Medical Center.


Nine East Network’s growing team of audiologists would like to offer FM equipment verification to schools in the future. We are currently working on developing company protocols so that we can conduct FM equipment verification as an additional service to Vermont’s schools and Deaf and hard of hearing students.


Check back on the Nine East Network blog for more information and future updates about the Vermont Deaf and Hard of Hearing Program!