by Neil Bauman, Ph.D.
1. Hearing Aids Do Not Correct Hearing to Normal
You might think that getting hearing aids would give hard-of-hearing people normal or near-normal hearing again. Surprisingly, the truth is that hearing aids only give you back about half of the hearing you have lost. This means that if you have an 80 dB loss like I have, with my fancy hearing aids, I can expect to hear as though I had a 40 dB loss. This is a blessing to be sure, but even with my hearing aids on, I still have a moderate hearing loss. As a result, I miss many things, especially in meetings and in larger venues such as churches and auditoriums. Thus, in addition to my hearing aids, I need further help from assistive devices such as loop systems.
2. Hearing Aids Are Only Effective for Distances Up to Six Feet
Shocking as it may seem, hearing aids are really only effective for distances up to six feet from the sound source. Sure, hearing aids will pick up many sounds from much greater distances, but the intelligibility of the sound decreases so as to be essentially useless at these greater distances.
This means that if the person I am talking with is less than 6 feet from my ears, I have a good chance of understanding him well. But, as the distance increases, hearing becomes harder and harder. I strain more and more to hear, but, at the same time, I understand less and less. The result is that I miss much/most/all of what the speaker says. This means that in meetings, church services and in auditoriums, I miss a lot because even though the building may have a million-dollar sound system, it’s loud-speakers are still considerably more than 6 feet from my ears. That is why, in addition to my hearing aids, I again need further help from assistive devices such as loop systems if I am going to hear and understand what is being said.
3. The Intelligibility of Speech Decreases as the Distance Increases
Hard-of-hearing people understand less and less of the spoken word as distance increases—even when wearing their fancy, expensive hearing aids. This is just the laws of physics in action.
Here are six facts about speech that will help you understand why this happens.
1. Speech is made up of both lower-frequency (<1,000 Hz) and higher-frequency (>1,000 Hz) sounds.
2. Lower-frequency sounds give speech most of its volume. (About 95% of the speech energy goes into making lower-frequency sounds.) At the same time, lower-frequency sounds only contribute about 40% of the intelligibility of speech.
3. Higher-frequency sounds add very little to speech volume. (About 5% of speech energy goes into making higher-frequency sounds.) However, this minuscule amount of speech energy contributes a whopping 60% to the intelligibility of speech.
4. Lower-frequency sounds travel considerable distances in air with relative ease.
5. Higher-frequency sounds are quickly attenuated in air so they don’t travel very far.
6. About 90% of the people with hearing loss have a high-frequency loss.
Now let’s put these facts together and see exactly what this means in practice for the average hard-of-hearing person. I think you will find this quite enlightening.
If you have a high-frequency loss, you hear the louder (lower-frequency) components of speech, but not the much-softer, higher-frequency parts of speech. Thus you hear people talking. That’s not the problem. However, because most of the intelligibility of speech lies in the higher frequencies, you don’t understand much of what they are saying. To you, speech sounds muffled and is largely unintelligible because you don’t hear the higher-frequency sounds that let you distinguish one word (syllable) from another. Thus, what you really need in order to understand speech better is more clarity.
Here’s the rub. The typical hard-of-hearing person needs more clarity (more higher-frequency sounds) in order to understand speech, yet it is these very frequencies that he can’t hear well at all.
At the same time, these vital higher-frequency sounds quickly attenuate in air. Thus, the further the hard-of-hearing person is from the sound source (the mouth of the person talking), the fewer higher-frequency sounds reach his ears. This double-whammy (not hearing higher-frequency sounds well in the first place coupled with the higher-frequency sounds “dropping out” of the air with increasing distance) leaves the hard-of-hearing person hearing mostly unintelligible (muffled) speech.
This is where assistive devices, such as loop systems, come in. With a loop system both lower- and higher-frequency sounds are captured by a microphone before the higher-frequency sounds are lost in the air. These sound signals are then amplified and “piped” to the t-coils in the hard-of-hearing person’s hearing aids without having to travel through the air as sound waves. The result is that the higher-frequency sounds are still there and the hard-of-hearing person hears beautiful, clear sound (or at least as beautiful and clear sounds as his damaged auditory system can produce).
This effect is remarkable. For example, one time, to prove the point, I stood near the back of a room that had a room loop system installed. With my hearing aids on (in microphone mode), I heard very muffled, mostly-unintelligible speech—so bad that if I didn’t speechread the speaker, I got nothing. Then I switched my hearing aids to t-coil mode. Instantly, I heard beautiful, clear speech—as though the person was speaking directly into both of my ears at the same time! That is what loop systems can do for us.
4. Loss of Sound Volume Is Not the Only Problem
Another thing that few people seem to realize is that loss of volume is not the only, or even the major, problem when you lose your hearing. If volume were the only problem, then amplification such as hearing aids would solve the problem. Unfortunately, along with hearing loss, we also lose some, or much, of our ability to discriminate between words with similar sounds. Thus, speech become “fuzzy”. We are never sure what you said is what we heard. This gives rise to so many of the “off the wall” comments made by hard-of-hearing people.
We hard-of-hearing people need as much clarity as possible so we can discriminate as well as our damaged auditory systems will allow. Again loop systems, because they capture the higher-frequency sounds and pipe them to our ears without attenuation makes hearing speech much clearer than using hearing aids alone.
5. Background Noise Is a Killer
Another serious problem with hearing loss is that we lose most of our ability to separate speech sounds from background noise as the ears of people with normal hearing can. This is because hearing aid microphones pick up, not only the wanted speech or music, but also any background noise present, other conversations and room reverberation.
Compounding the problem is that with hearing aids so often all we hear is foreground sounds—because everything we hear is in the foreground—both the speech we want to hear, and the background sounds that make it hard or impossible for us to understand speech when other sounds are present. That’s just the way things are when you have a hearing loss and wear hearing aids.
Furthermore, people with normal hearing can pick out speech from the background sounds when the signal-to-noise ratio is as low as 0 dB (the speech and the background sounds are at the same level), although they do much better if the speech sounds are somewhat louder than the background sounds (about 5 dB).
In contrast, hard-of-hearing people need a large degree of separation between speech and the background sounds (at least a 15 dB signal to noise ratio) so they can hear speech clearly. Loop systems when properly set up and attached to a properly-adjusted sound system do even better. They give a minimum of a 20 dB signal-to-noise ratio. This lets us hear speech clearly.
The reason loop systems can give a 20 dB signal-to-ratio is because typically the microphone is close to the speaker’s mouth so it only picks up the speech sounds and not the background noise or reverberation in the room. In addition, because we listen via the room loop and the telecoils in our hearing aids, we only hear what is coming from the sound system since the microphones on our hearing aids are turned off. Again, this gives beautiful, clear sound via a loop system.
As you can see, loop systems (and other assistive device technologies such as FM and infrared when used with neckloops) largely eliminate the two main limitations of hearing aids and, as a result, can turn our hearing aids into awesome listening devices. The result is that we both hear and understand a lot more than we other would.