|By Cheryl Heppner, 8/11/11
Continuing the presentation by Dr. Matt Bakke and his colleagues at the HLAA Loop conference
A telecoil is considered low tech but results in high yield due to its effectiveness. It must be programmed competently by an audiologist for full effectiveness.
Factors Affecting Communication Access
People over the age of 60 with hearing loss tend to do less well at understanding in a noisy environment. Many people also have vision loss.
All the advances in technology cannot overcome certain other factors that are important to communication access. These include talker factors, auditory factors and visual factors.
The habits of each individual speaker have an impact on how effectively a person with hearing loss can understand them. Among them are: clear articulation of speech, speed of talking, whether the speech has a foreign or regional accent, and whether words are emphasized to better convey meaning.
How sentences are spoken, (which can add color to speech) can increase or decrease the interest of listeners. Word stress is “the music of speech.” When speech is modulated instead of monotone, it conveys feelings and keeps listeners interested. Control of the speech rate, so the speaker is not rushing through, is also important.
Good habits include making eye contact with the audience and moving around instead of being rooted on a stage or podium. Use of visual media to reinforce what is being said, and correct use of captioning, or interpretation for those who know sign language, also helps to support speech understanding. A key element in making captioning or interpretation effective is to prepare the captioner or interpreter in advance so they are familiar with what will be covered.
Signal to noise ratio (SNR) is defined by Wikipedia as a measure used in science and engineering that compares the level of a desired signal to the level of background noise.
Signal to noise ratio makes a significant difference in communication access. Dr. Bakke gave this simple rule to remember: size matters; bigger is better.
Several studies have looked at what is a minimally acceptable level is for signal to noise. One study was done in 2007 by Wilson, et al.
In 1999, Dr. Bakke attempted to determine what the minimally acceptable SNR was for loop-generated audio.
During Dr. Bakke’s study information was captured on what the participants judged to be excellent signal to noise ratio. One of the things learned was that loops generate white noise. The bare minimum for an acceptable level of SNR was found to be 18 dB, but higher numbers gave good to excellent ratings.
An interesting finding in this study was that the acceptable level was the same for all degrees and configurations of hearing loss. Thus, the goal is to achieve the highest possible SNR while maintaining a comfortable sound pressure level.
Reverberation, the echo within a room or space, is also an issue. The negative effect of reverberation increases the further the distance between the microphone and the mouth of the speaker. This is because the intensity of the signal drops as the microphone moves away from the mouth.
Another study by Dr. Bakke and his colleagues in 1999 took measures in three rooms. It found that in one room the microphone was only acceptable if it was not more than three feet from the talker and that holding it 3 three inches was much better. But this was only true in that one room. The general rule was that the closer the microphone to the mouth, the better.
While Dr. Bakke is not aware of acceptability rating research on frequency response, he noted that, based on the limits of today’s hearing technology, assistive listening systems should provide no less than 4000 Hz, and more if acceptable.
Hearing Loop Conference