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ASSISTIVE LISTENING DEVICES
What They Are
Assistive Listening Devices (ALDs) are those products, aside from hearing aids, that assist people in understanding speech, enjoying music, and being alerted to important sounds like the telephone, doorbell, and smoke alarm. They have become more important recently due to the passage of the Americans With Disabilities Act (ADA) and its requirement for these devices to be available in public accommodations and in the workplace. There has never been a major effort to market these devices widely to the hearing impaired population, who remain uninformed of their existence.
What They Do
Enable Understanding By Increasing Speech-To-Noise Ratio (SNR): Ninety five percent of hard of hearing people have a sensorineural (high frequency) hearing loss. They may hear speech sounds but cannot understand them because the consonants are high frequency, low power, sounds. Without the consonants, words cannot be understood. Hearing aids generally boost these missing frequencies to the extent of the decibel loss and are fairly effective in low noise "living room" situations. However, distance to the sound source and level of background noise, especially speech babble, destroy the effectiveness of the hearing aids. In situations of high background noise, such as a noisy cocktail lounge, the aids actually worsen the ability to hear. Assistive listening devices in these situations simply pick up the sound much closer to the source, thus eliminating background noise and increasing the speech-to-noise ratio to a point that understanding is possible . At the same time, similar to hearing aids, they accentuate the high frequencies. The all-important speech-to-noise ratio is thus enhanced to the extent that the person may now both hear and understand what is being said. This is accomplished either with personal amplifiers with extendible microphones wired to them, or with FM transmitter-receiver combinations where the transmitter with mic is placed near or on the sound source and the receiver is used to hear the transmitted voice at a distance from the source.
Alert People To Telephone, Doorbell, Alarm Clock, Smoke Alarm, Etc.: Persons with severe to profound losses normally cannot hear many types of environmental noises, especially without their hearing aids. In these cases, sound detectors are used to pick up the particular sound and then flash a light or activate a vibrator to alert the person.
Enable Telephone Communication: Equipment to enable people who cannot carry on a conversation using a standard or amplified telephone is available. Presently called a TTY (formerly TDD), this is a typewriter-like device using the standard QWERTY typing set that either plugs directly into the telephone line or has acoustic cups allowing a normal telephone handset to be connected to the device. The user then types their message. The recipient must also have a TTY connected to the telephone to receive the message. Recent federal legislation mandated relay operators in each state to provide intermediary service by a third person between someone with a TTY and another person using the telephone normally.
Why You Need ALDs >>>>>>> They Help When Hearing Aids Can't
As a person becomes hard-of-hearing, and almost all of us do as we age, the first thing we notice is that people seem to be mumbling. The lack of high frequencies in your hearing destroys the intelligibility of the spoken word. If you get hearing aids, the problem is often solved for low noise, close-up situations. But this is only a small part of the real world, and this is what frustrates people. When they are in automobiles, restaurants, on the street, in movies, auditoriums, or large spaces, they quickly find they can no longer hear with hearing aids. Realizing this, many hearing aid manufacturers and dealers advertised, "XYZ HEARING AID ALLOWS YOU TO HEAR WITH BACKGROUND NOISE". This was entirely false and misleading advertising and, after being warned several times by the Food and Drug Administration, the FDA imposed sanctions on the leading companies, which included the biggest names in the industry.
In other words, it is widely recognized that the inability to hear in background noise is the No.1 problem and complaint -- after the price of hearing aids!. Why then don't most hearing aid dispensers and audiologists inform their clients and/or sell them ALDs which incontestably reduce background noise and allow communication? Three reasons: a) They don't know much about them; b) ALD's have a much smaller profit margin (40-60%) than hearing aids (300-600%) and cost much less; c) They are afraid that ALDs will compete with their hearing aid business..
GET THIS: Transmitters have almost NOTHING to do with how well you understand what you're listening to, so don't worry about what transmitter comes with an ALD system. Transmitters have more to do with how FAR you can listen and still pick up the signal. However, it's important to decrease background noise (increasing SNR) by getting the transmitter microphone near the source of sound, or plugging the transmitter directly into the sound source (TV, VCR, public address system amplifier, etc.).
Receiver quality and design, however, have almost EVERYTHING to do with how well you can understand. Hard-Of-Hearing (HOH) people need more SNR (signal-to-noise ratio --or-- speech-to-noise ratio) to be able to understand. This is primarily accomplished in two important ways:· (1) By having a receiver that increases the higher frequencies (signal) and (2) also inhibits the lower frequencies (noise). Thus this type of receiver also increases the all-important SNR.
Why does this type of receiver increase your understanding? Ninety five percent of HOH people have a high frequency loss. The high frequencies, which are the consonants in speech, are also the low power elements of speech. Vowels are higher power, lower frequency elements. So we tend to hear the vowels but miss the consonants. Let's suppose that you write a word on the blackboard. Then erase the consonants, leaving just the letters A, E, I, O, or U. What are your chances of understanding what is written? Slim to none is the answer. This is why a receiver with excellent high frequency amplification is important to understanding.
So do all ALD (assistive listening device) receivers have a great high frequency boost? Mostly NOT! Why? I don't know. I can only guess that most, if not all, design engineers have normal hearing and must not realize the extent to which HOH people need the high frequency boost -- as much as 15dB SNR (5.6 to 1) or more in noisy situations. This means that the speech sound must be 5.6 times higher than the background noise level. If a person with normal hearing listens to a receiver with significant high frequency boost, it may sound tinny or scratchy to them. But not to HOH people! Don't they test these out on HOH persons?
II AN IMPORTANT WORD ABOUT HEARING WITH WIRELESS SYSTEMS
Some people often become frustrated with their hearing aids because they can't hear well in restaurants, in automobiles, in movie theaters or auditoriums, and in most other situations in which there is some degree of background noise and/or some distance to the sound source. The result is that these people think they can't be successfully fitted with aids and they "give up". They stop wearing the aid and never return to their audiologist or dispenser. Here's a flash for those people:
1) Hearing aids can enhance the quality of your life significantly in low noise, "living room" situations.
2) No matter what you have been told or heard, hearing aids will NOT function well, if at all, in higher noise situations, especially background speech noise, or at distances more than 8 feet. The actual distance at which you can hear (and understand) with hearing aids will depend upon:
· >The amount of background noise
· >Distance to the speaker
· >The frequency (tone) of the speaker's voice.
People with a hearing loss need a higher speech-to-noise ratio (SNR) than those with normal hearing. The best way to accomplish this is simply to get closer to the source of the sound. You can do this by putting your ear within an inch or so of the speaker, but this may become embarrassing in a house of worship, for example, when the speaker is the reverend. Or the speaker may be someone sitting across the table from you in a restaurant. Picture yourself dipping your tie or blouse in someone's soup as you lean across the table to hear. The answer, of course, without getting too much sillier, is the assistive listening device (ALD). These devices provide two important functions, vital to understanding speech:
· >They get you closer to the sound, usually utilizing a microphone. This cuts down the background noise and improves the all important speech-to-noise ratio (SNR) dramatically .
· >A good ALD amplifier will enhance the high frequencies, keeping the lower speech frequencies at the same level or attenuating them. This is important for the 95% of us with a high-frequency (sensorineural) loss because obviously we need the highs emphasized. But holding down the low frequencies also helps because the lows tend to interfere with our ability to detect high frequencies. This is a physiological phenomenon called "upward spread of masking".
LONG DISTANCE SITUATIONS : 8+ Feet: If you had a microphone on a 100-foot cord attached to your hearing aid, you could hear under most circumstances by placing the mic near the sound source. For obvious reasons this is impractical. For long distances (note we are defining this as near as 8 feet) we use two approaches, both utilizing sound transmission, usually FM radio wave, or Infrared light wave.
1) The Classroom/Lecture/Tour-Guide Situation: this is where you use a personal portable battery-operated wireless FM transmitter with lapel mic that is carried by the person speaking. A receiver with earphone, headset, CI Cord, or neckloop is used by the listener(s). Maximum operating distance may be as much as 1500'. A system such as this consisting of a single transmitter and receiver can be obtained for under $200.
2) The Square Dance/Theater/Church/Auditorium/ Wide Area Situation: Complete assistive device systems for these situations normally cannot be brought to the facility (church, movie) by you, although many people have donated one to their house of worship. The fixed base transmitter (plugged into an electric outlet) must be installed by the facility itself and connected to their sound source (movie projector, PA system, etc.). The assistive device system is owned by the facility. However you may bring your own receiver (Infrared or FM, depending on the type of system installed) or get one from the facility usually surrendering your driver's license or your spouse at the main entrance. A transmitter and four receivers for these "wide area" systems can cost as little as $454.99.
SHORT DISTANCE SITUATIONS - Up To 8 Feet: Hearing with background noise at close distances is easily solved by using a personal amplifier like the Williams Sound Pocketalker, $149.99 (See "Hearing With Background Noise"), for listening in restaurants, cars, at card games, and in small groups. Good amplifiers should provide an excellent high frequency audio response with close to 50 dB of average gain in the higher speech frequencies. Listening may be with earphone, headphones, neckloop, CI Cord, or any device that you can plug into the amplifier which usually have a 3/8"(3.5 mm) jack. .
One of the most frustrating things I deal with is trying to get someone with a severe or profound loss to be able to understand sufficiently on the telephone to carry on a conversation. And I'm usually trying to help them by phone! Even when a particular telephone amplifier has adequate volume, in many cases it does not provide enough high frequency boost for word clarity and understanding.
Severe to Profound Loss: 85-100+ dB
With very severe to profound losses, it is mandatory to use hearing aid's with T-switches for telephones and assistive listening devices so that you can use the amplification of your hearing aid(s), which presumably has been optimized for your particular loss. But here we run into a problem, and this is important to know:
Many T-coils are not electronically "matched" to your hearing aid amplifier, as is the hearing aid microphone. The result is that when you switch to the T-coil, the frequency response of the hearing aid may change significantly because of the mismatching, making the sound that you hear (now being brought in via the T-coil rather than the microphone) not as clear as with the microphone. The answer is to have your T-coil changed to a "Power Coil" type of circuit. This is a T-coil circuit with a preamplifier which increases the volume through the T-coil circuit, and "matches" the T-coil circuit to the amplifier in the same way the microphone circuit is matched to the amplifier. You will now get the same volume and same frequency response from both circuits. So for very severe to profound losses, a good T-coil circuit is extremely important for communicating on the telephone or using assistive devices.
Moderate To Severe Loss: 60 To 85 dB
In many instances it is more comfortable and more effective to be able to use the telephone directly, without the use of a hearing aid. This is especially true if you have long or frequent telephone conversations. In this case, a good telephone amplifier is required. With mild to moderate losses, this is not a problem. Almost any amplifier on the market will usually suffice although some have a better (high frequency) response than others. However there are many people with a moderate to severe loss who are marginal. They have been able to hear using an amplifier in the past but are now having problems. I hear from them by the scores, and get frustrated trying to get them the right product. Two possibilities for moderate to severe losses are 1) Using one of the new high-gain or double-amplified telephones (most of these now have an audio output jack which enables you to listen with headphones, neckloop, etc.) 2) Using a Model 1693 Amplifier with graphic equalizer to tune for your particular hearing loss.
Remember however: Assistive devices are not like eyeglasses. You have to try out different devices. The reason for this is that the cochlea is not the only thing determining how well, and what, you will hear -- there is also post-cochlear processing by the auditory nerve and brain. Very little is known about the processing that goes on there. But I know from experience that two people with identical audiograms can differ greatly in how well they hear on the telephone and elsewhere. For this reason, one can't accurately predict which device will work best
Hearing Aids – THE HYPE, THE BALONEY -- THE NO SPIN ZONE
Joe Marin – B.S., B.A., M.S.
I’ve read the write-ups in trade magazines about various advances in hearing aid circuitry for many years. The latest, of course, are the digitals. These engineering-type articles are usually written by people employed by or associated with a manufacturer and, for the most part, are meant to provide a scientific basis for the their latest designs. HOWEVER, the implications of “breakthrough technology” in these articles can be seriously misleading in many ways. The comments that follow are based the laws of physics, engineering design and my experience as a HOH person..:
*** THIS HYPE IS FOR YOU: Many, perhaps most, dispensers can’t understand or follow these articles because of the article's highly technical nature. But the manufacturer’s marketing people (who don’t understand them either) take these “advances” and run with them, emphasizing words and phrases like “dsp” (digital signal processing), “optimal compression ratios”, and “wide dynamic range compression” (WDRC) in their advertising. Now most of this circuitry really does change the H/A response in ways that enhance WHAT IS BELIEVED to be related to our hearing mechanism; that is, primarily, the cochlea’s response to sound. The problem is that scientists, to this day, DON’T KNOW exactly how we hear, and therefore do not have an accurate model to go by. This is probably due to the unknown post-cochlea processing that occurs in the auditory nerve and brain. The result is that some people will be helped to some extent, and some people (even with an identical audiogram) will spend $3000 for the hype. Almost half the people (46%) buying aids are unsatisfied according to The Hearing Journal.
*** THIS HYPE IS FOR THE DISPENSER: The dispenser is the main target for the hype. There are ads in every trade magazine using all the buzz words to convince them of the superiority (and the rationale for charging more) of one aid over the others. And I imagine a department within every manufacturer whose only job is to come up names for the new aids: Prisma, Signia, Triano (Siemens); Canta (GN Resound); Axent (Starkey); Sierra (Electone), …ad infinitim.
*** NOISE REDUCTION – THE BALONEY: Many articles deal with the elimination of “noise” since this is a primary complaint of H/A users. Several aspects are important:
1. Much noise reduction is very simple to solve because any type of H/A – digital or analog -- eliminates noise, PROVIDED THE NOISE IS OUTSIDE THE SPEECH FREQUENCIES. But some noise is usually present within the speech frequencies (especially other speech), so we derive the “speech-to-noise” ratio (SNR) – also known as “the signal-to-noise ratio". This is the proportion of speech energy to the unwanted sound. The higher the SNR, the better is our understanding. The problem is that in many ads and some articles, “noise” may be ambiguously defined and may contain varying degrees of speech noise or not contain speech noise (babble) at all!. This is a SCAM because, as mentioned, unless the noise frequencies are in the speech frequency range being amplified, they are attenuated by the H/A. And some H/As include a bass-cut switch or channel which further reduces the lower frequencies where much (non-speech) environmental noise resides. Ads for these aids will say “Noise Reduction Circuitry”, or “Hear In Noise”. A few years ago, after many warnings, the FDA fined these companies and told them to cease and desist from this misleading advertising. The companies included the biggest names in the business.
2. Now, with the advent of digital processing, we are getting articles claiming to reduce noise with dsp (digital signal processing) alone, or in combination with aids having unidirectional microphones. These articles claim about a 2-7 dB increase in SNR. HOWEVER, THIS IS PEANUTS compared to the requirement of HOH people who need 15+dB SNR, especially with hefty background noise. Again, the ads say “Hear In Noise!” …not on this planet!
*** REAL NOISE REDUCTION – THE SCOOP: Significant noise reduction with commensurate increase in the SNR is actually possible in today’s world, but not with any magical digital processing – not yet at least. The advances in digital processing circuitry do provide small increases in speech intelligibility along with some other “bells and whistles” – feedback reduction, etc. But not nearly enough, in my view, to be thought of as “significant” by most HOH people. And not enough to justify the additional cost. The secret to hearing with background noise? GET CLOSER to the sound source by putting a mic near it, or plugging into it and having it transmitted directly to your ear or hearing aid. The downside is that you usually can’t hear other sound sources at the same time without each of them having an input, such as is found in government committee rooms, the UN, and other “wired” places. The upside is that these gadgets cost one tenth of the cost of the much hyped H/As, and ACTUALLY WORK!