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Identify different types of hearing devices Contents Key to resources 2 Introduction 4 Different types and styles of hearing aids (devices) 5 Different types of assistive listening device (ALD) 7 Other hearing devices 9 Hearing device components 10 Analogue and digital hearing aids (devices) 14 Glossary 15 Feedback to activities 17 1 © NSW DET 2008 Key to resources for activities Note: Print this Key to resources for activities and refer to it as you work through the task guide. Resource number Resource title 1 Dillon, H (2001) Hearing Aids, Boomerang Press, Sydney Chapter 1: Introductory concepts Section 1.3: Types of hearing aids Chapter 10: Selecting and adjusting hearing aids Section 10.1: Selecting hearing aid style Complete Your Case Studies, Slide 2, to review this topic 2 Dillon, H (2001) Hearing Aids, Boomerang Press, Sydney Chapter 3: Hearing aid systems 3 Section 3.11: Assistive listening devices. This gives a useful overview of ALDs’ specific uses. Sections 3.5–3.10: These sections offer more of an insight into these ALDs. Sections 3.2–3.4: Concentrate your reading on Section 3.4, particularly 3.4.5. Dillon, H (2001) Hearing Aids, Boomerang Press, Sydney Chapter 16: CROS, bone-conduction, and implanted hearing aids Section 16.2: Bone-conduction hearing aids (Introduction) Section 16.2.1: Applications of bone-conduction hearing aids Section 16.2.4: Disadvantages of bone-conduction hearing aids Section 16.3: Implanted and semi-implanted hearing aids Section 16.3.1: Bone-anchored hearing aids Section 16.3.2: Middle-ear implants See also Martin, FN and Clark, JG (2006) Introduction to Audiology (9th edn), Allyn & Bacon, Boston. Go to Chapter 8: The inner ear, then turn to the section on ‘Vestibular mechanism’. The website Hear-it <www.hear-it.org> provides useful summaries of each of the devices in Dillon’s chapter. Look in the ‘Facts’ section of the site. To find out more about BAHAs, see Cochlear (a manufacturer) at <www.cochlear.com.au>. To find out more about middle-ear implants, see Vibrant Med-El (a manufacturer) at <www.vibrant-medel.com>. 2 © NSW DET 2008 Complete Your Case Studies, Slide 2, to review this topic. 4 Dillon, H (2001) Hearing Aids, Boomerang Press, Sydney Chapter 2: Hearing aid components Section 2.1: Block diagrams Look especially at Figure 2.2, which is a representation of a three-channel compression hearing aid in block diagrams. The last paragraph of this section gives you a good summary. Section 2.2: Microphones Section 2.3: Amplifiers Section 2.6: Receivers Section 2.5: Tone controls and filters Sections 2.8–2.10 Section 2.12: Batteries Section 2.4: Digital circuits Find out about some of the initial advantages of digital processing over analogue processing. Complete Your Case Studies, Slide 2, to review this topic. 3 © NSW DET 2008 Introduction In this unit we are going to look at what makes up a hearing device. We’ll start by looking at hearing aids (devices) from a distance, in all their variations. Then we’ll quickly zoom in, break open the cases of a few hearing devices and look at the bits that fall out. Then we’ll start to move back again, putting the pieces together to see how and why different hearing devices are produced. But why is it important to have an understanding of how hearing aids (devices) work? Imagine for a moment that, sitting in front of you, is your next client, Mrs Bessie Tulliver. Mrs Tulliver is relying on you to help her select the best hearing device for her hearing loss and needs. There are two hearing aids (devices) that seem to best match her hearing loss: the outstandingly named Concorde Supersound, and the Symphonic Dulcette. But which is best? Surveying the impressive list of things each hearing aid (device) is supposed to do, you see that the Supersound uses “six intelli-bands to constantly adjust the incoming sound to maintain a perfect signal level and removes interfering noises using the patented beamformer and noise-delete systems, which together pinpoint the people you want to hear, all housed within an almost-invisible, stylish, ergonomically designed post-auricular range of cases”. The Dulcette, on the other hand, is described as “a small, behind-theear aid (device) which compresses the sound within seven digital channels, suppresses ambient noise and uses adaptive directional microphones”. Would you know that the Supersound, at almost twice the price of the Dulcette, appears to be essentially very similar? As we consider the technology involved in a modern hearing device, we will be using the first 10 chapters of your textbook Hearing Aids by Harvey Dillon. We’ll be dipping into it so that, at the end of this unit, you will have a very good grasp of where to look in the text to find the answer to a question, as well as what makes up the common, garden-variety hearing aid (device). 4 © NSW DET 2008 Different types and styles of hearing aids (devices) Sometimes ‘hearing aids’ and ‘hearing devices’ are used to mean the same thing. However, as we will see, there are many more hearing devices than just hearing aids. Hearing aids are just one group of hearing device. Nonetheless, hearing aids are the largest and most common form of hearing device, so let’s consider them first. Hearing aids (devices) come in a vast array of shapes, sizes, colours, styles – and each hearing aid (device) manufacturer has its own variety. The following links give you a taste of the ranges from most manufacturers represented in Australia. They are listed alphabetically by manufacturer name. You don’t need to work your way through them all, but if you do, you’ll gain a bird’s-eye view of the current hearing aid (device) market. Bernafon International: <www.bernafon.com.au> Interton: <http://interton.com> Oticon: <www.oticon.com.au> Phonak: <www.phonak.com> ReSound: <www.gnresound.com> Siemens: <www.siemens-hearing.com.au> Sonic Innovations: <www.sonici.com> Starkey: <www.starkey.com> Unitron Hearing: <www.unitronhearing.com.au> Widex: <http://sc.widex.com> Note that some of these links are to Australian websites, and others are to international websites. At time of writing, some manufacturers’ Australian websites were not up to date! This is worth noting, as some of the hearing aids (devices) you read about might not be available in Australia. One of the reasons the Australian websites might not be current is that hearing aid (device) manufacturers are continually producing new ranges, so keeping the website up to date is a full-time job. The best way to find out which hearing aids (devices) are available in Australia is to contact the companies directly by phone and ask. If you’ve looked at only a few of the above links, you may be feeling a bit overwhelmed. There are, however, only five basic types of hearing aid (device): Body Aid Behind-The-Ear (BTE) aid In-The-Ear (ITE) aid 5 © NSW DET 2008 In-The-Canal (ITC) aid Completely-In-the-Canal (CIC) aid. There are also several uncommon hearing aids (devices), such as the Spectacle Aid and the Bone Conductor Aid, which have special applications. Of the five basic types, by far the most commonly fitted are the BTE and ITC. Activity 1 Go to Resource 1 1. Which style of hearing aid (device) is least visible to others? 2. Which style/s of hearing aid (device) is/are most reliable? 3. Which type/s of hearing aid (device) is/are easiest to clean? 4. Which type of hearing aid (device) is least sensitive to wind noise? Feedback is provided at the end of this document. Sometimes a conventional hearing aid (device) is not appropriate. For example, your client may really only have difficulty hearing on the phone, but in all other situations they manage without significant difficulty. Fitting a hearing aid (device) might help them with the phone, but it’s rather like providing someone who has difficulty reaching down to pick up things from the floor with a miniature crane. A pair of tongs might do just as well, and be less trouble to use. In instances such as this, an assistive listening device (ALD) might be more appropriate. 6 © NSW DET 2008 Different types of assistive listening device (ALD) ALDs can be fitted instead of hearing aids (devices), and they can also be fitted to work in conjunction with hearing aids (devices). ALDs usually perform more specialised functions than hearing aids (devices), and are thus chosen according to specific need/s. In this section it may seem as if we’re jumping around the textbook randomly, however all you need to grasp is a taste of the variety and range of options available. Activity 2 Go to Resource 2 Now that you’ve read this, name three ALDs which could be used for someone (with or without a hearing aid (device)) who has difficulty hearing on the phone: Feedback is provided at the end of this document. ALDs can be used with or instead of hearing aids (devices), in situations where a conventional hearing aid (device) either does not help, or cannot be successfully managed. For example, a readily available ALD is the Binaural Listener, in which a microphone, amplifier and battery are housed in a box which is similar in shape and size to a personal stereo. Lightweight headphones are connected to the box. For people who have severely reduced sensitivity and manipulation ability in their hands and fingers, the Binaural Listener is a good alternative to a conventional hearing aid (device). The headphones are larger and more easily placed on the head by the client or carer. The controls on the box are 7 © NSW DET 2008 large and can be held in front, so are much easier to use than the little controls on a conventional hearing aid (device). There are many examples of this type of ALD on the market. Most hearing aid (device) companies supply a few options. Several companies, such as Printacall <www.printacall.com.au> and Word of Mouth Technology <www.wom.com.au> specialise in ALDs and carry a large range. There are also a number of ALDs available through electronic stores such as Dick Smith, Tandy or JB Hi-Fi, and from manufacturers of other sound equipment, such as Sennheiser (available from Syntec at www.syntec.com.au). The company Phoenix Hearing Instruments carries a very large range of ALDs and many hearing aid (device) options. Examples can be found on their website <www.phoenixhearing.com.au>. Many ALDs are used in conjunction with hearing aids (devices). Hearing aids (devices) perform well at close range and in quiet environments. They perform less well at greater distances and in noisy conditions. ALDs can be used to help improve the performance of a hearing aid (device) in the face of these difficulties. Activity 3 Go to Resource 2 1. Lady Catherine de Bourgh has a moderate sensorineural hearing loss but is no longer able to manage to insert a conventional hearing aid (device). Her audiometrist has tried ITEs and BTEs. What could she use instead? 2. Mrs Profound has been finding it increasingly difficult to talk on the phone, and lately has been avoiding picking it up, because she can’t understand anyone any more. Her hearing aid (device) is functioning appropriately, and it is apparent that she relies on lip-reading to communicate. What options could you suggest to Mrs Profound to help her with the phone? Tick all that apply. (a) Suggest a different kind of hearing aid (device). (b) Give her information about the National Relay Service. 8 © NSW DET 2008 (c) Give her training in using the telecoil on her hearing aid (device). (d) Give her information about Telephone Typewriters (TTY). (e) Suggest that she may consider a cochlear implant. (f) Suggest a volume-control phone. Other hearing devices Hearing aids (devices) and ALDs go a long way in helping people with hearing loss and other associated difficulties. However, sometimes a person may have specific physical conditions which make a conventional hearing aid (device) and/or ALD inappropriate. In these cases, alternatives must be considered. Go to Resource 3 Sometimes a person has such significant difficulty hearing that none of the above hearing devices and/or ALDs are able to significantly improve their communication abilities. In these cases, one of several alternative devices may be appropriate. The most common of these is the cochlear implant. Invented by Professor Graeme Clark (Melbourne), the cochlear implant has significantly improved options for people with very significant hearing losses. Go to <www.audiology.asn.au> to read a short description of how the cochlear implant works. Brainstem implants are another type of device which provide a sensation of sound for people who are unable to benefit from a hearing device, ALD or cochlear implant. Read more about brainstem implants at <www.hearit.org>. There are other implantable and semi-implantable devices about, however these are the main ones. It’s vital that, as hearing professionals, we’re aware of the array of hearing aid (device) options available, including the less common ones, as you never know when you may meet someone who needs one. You may be the first point of contact for someone who needs a BAHA implant. Although you may not be the person to fit the BAHA, your client will depend on you to refer them to the person who will. Now let’s focus on the components that make up the most common hearing aids (devices), which we looked at in Resource 1.0 9 © NSW DET 2008 Hearing device components The BTE, ITE, CIC, Body Aid and Spectacle Aid all have in common the key components which form the building blocks of any conventional hearing aid (device). The key building blocks of a hearing aid (device) are: microphone amplifier filters and processors receiver (the little loudspeaker). Sound signals are converted to electrical signals by the microphone. These electrical signals are then modified by the amplifier/s, filters and/or processors. The resultant electrical signals are then converted back into sound signals by the receiver. Activity 4 Go to Resource 4 Use Resource 4 for the remainder of this task guide. Having read these sections of your textbook, draw the block diagrams for the following components next to their name. Microphone: Amplifier: Receiver: 10 © NSW DET 2008 Feedback is provided at the end of this document. Microphones, amplifiers, receivers and filters Let’s now look more closely at each of these components. Go to Resource 4 The earliest form of electronic hearing aid (device) consisted of a microphone, battery and receiver, with the receiver providing its own amplification. Amplifiers were soon added, allowing greater amplification of the signal. As you know, hearing loss for most people is not equal at all frequencies. For most people there is a greater degree of loss at some frequency regions than at others. For such people, equal amplification at all frequencies does not provide the best possible result. It is for this reason that filters are used in hearing aids (devices), allowing some sound frequencies to be amplified more, and other sound frequency regions to be amplified less. Telecoils and DAI There are two other common electrical hearing aid (device) components: the telecoil and direct audio input (DAI). These both allow the hearing aid (device) to receive a signal from another device. In the case of the telecoil, the signal is received magnetically, and in the case of the DAI the signal is received electronically (through a plug). Go to Resource 4 Using the telecoil, a hearing aid (device) can pick up signals from induction loop systems. A loop system is a loop of wire usually connected to a public address system of some kind. A common use is in a church, where the loop system is placed around the seating area. Another common use of a loop system is in a cinema, where the person can use their telecoil to listen to the movie soundtrack. Because the telecoil is picking up the soundtrack, the microphone on the hearing aid (device) can be switched off, so the loud crunching and munching of potato chips from the row behind is not amplified by the hearing aid (device). 11 © NSW DET 2008 Fast-forward your textbook for a moment to Chapter 3, and reread Section 3.6 (‘Induction loops’) to revise your understanding of how this works. Another use for the telecoil is with the phone, where it can again provide a clear signal with less interference. Using DAI, a hearing aid (device) can pick up signals from a range of audio devices and hearing aid (device) assistive listening devices. For example, a client’s iPod can be plugged directly into the hearing aid (device); likewise, the sound output from a computer can also be plugged directly into the hearing aid (device). A Bluetooth device can be plugged into the hearing aid (device), enabling the hearing aid (device) to receive signals from Bluetooth devices such as mobile phones. Remote controls One accessory for use with hearing aids (devices) is a remote control. The remote control allows the hearing aid (device) to be adjusted remotely, and so reduces the need for controls on the hearing aid (device) itself. Go to Resource 4 Batteries Finally, no electronic hearing aid (device) will function without a source of electricity. In early-model hearing aids (devices), the battery was similar in size to a moderate car battery, however they are now quite a bit smaller. Activity 5 Go to Resource 4 1. Which is correct? Tick the correct answer. Modern hearing aid (device) microphones: (a) create no noise of their own (b) are sensitive to vibrations 12 © NSW DET 2008 (c) have a magnet and diaphragm (d) have a completely flat frequency response 2. The most efficient type of hearing aid (device) amplifier is the Class B. True or false? 3. Hearing aid (device) receivers operate using: (a) electrical forces (b) pressure forces (c) astral forces (d) magnetic forces 4. Name the following filters: a. a filter that provides more gain to frequencies in a certain band: b. a filter that allows more gain to high frequencies than low frequencies: c. a filter that allows more gain to low frequencies than high frequencies: 5. Hearing aid (device) telecoils pick up magnetic signals. True or false? 6. Hearing aid (device) batteries last all year, just like watch batteries. True or false? Feedback is provided at the end of this document. All the components listed above are connected together in similar ways to form a functional hearing aid (device). However the finished product doesn’t always look the same. Now it’s time to go back inside the hearing aid (device), and consider in more detail how the heart of the hearing aid (device) modifies the sound signal to produce a better result for the person wearing the aid (device). 13 © NSW DET 2008 Analogue and digital hearing aids (devices) First, let’s discuss the difference between analogue and digital signal processing. Go to Resource 4 Initially all hearing aids (devices) were analogue (analog) hearing aids (devices). In an analogue hearing aid (device), when you follow the sound signal as it is converted into an electrical signal and then back into a sound signal, you will find that the electrical signal is analagous to the sound signal. That is, if you were to draw each signal on paper, they would look like each other. In the early 1990s, digital hearing aids (devices) started to appear. The key difference between analogue and digital hearing aids (devices) is in the amplifier and filter section of the hearing aid (device). Whereas in an analogue hearing aid (device) all the signals retain the original shape of the sound signal, in a digital hearing aid (device), all the signals are converted into a digital signal – a combination of 0s and 1s. Activity 6 Go to Resource 2 1. Write three key advantages of digital over analogue for hearing aids (devices). 2. Write down the point Harvey Dillon makes regarding what digital aids (devices) can’t do: 14 © NSW DET 2008 Feedback is provided at the end of this document. The heart of an analogue hearing aid (device) is the amplifiers and filters. In the digital hearing aid (device) the heart is the digital signal processor. As almost all new hearing aids (devices) are now digital, this will be our focus of our discussion, however the discussion can be applied to any method of sound processing. Glossary Acoustic hearing aid (device) effects Anything non-electrical that affects the sound reaching the eardrum (pinna, microphone tubing, ear hook, ear mould tubing, ear mould/ear shell, sound bore, venting, ear canal) ALD Assistive listening device BTE Behind-The-Ear hearing aid (device) CIC Completely-In-the-Canal hearing aid (device) Digitally programmable The settings of a digitally programmable hearing aid (device) are adjusted by a computer or programming device. This allows for much greater flexibility in adjustment than is possible using trimpots. Note that a digitally programmable hearing aid (device) is an analogue aid (device) Electro-acoustic hearing aid (device) effects Anything that pertains to the hearing aid (device) transducers (microphone, receiver and everything between them) ITC In-The-Canal hearing aid (device) ITE In-The-Ear hearing aid (device) MC Mini-Canal hearing aid (device) MPO Maximum power output : this is usually used to mean OSPL90 NRS National Relay Service: an Australian government service which allows a person using a TTY to communicate with someone who does not have a TTY (see <www.relayservice.com.au> for more information) OSPL90 The (output) SPL (sound pressure level) produced by a hearing aid (device) when it receives a 90dB input Peak clipping A method of maximum output limiting in which the peaks of the signal that would otherwise be greater than the maximum level are ‘clipped’. As a result there is no reduction in gain, but there is significant distortion REIR Real Ear Insertion Response. REIG stands for Real Ear Insertion Gain, while IG stands for Insertion Gain. Note that REIR, REIG 15 © NSW DET 2008 and IG are generally used interchangeably REUG Real Ear Unaided Gain; note that REUR and REUG are generally used interchangeably REUR Real Ear Unaided Response Signal-to-noise ratio (S/N or SNR) A measure of the level of the desired signal, relative to the level of undesired signal (background noise). The larger the SNR, the less the undesired signal masks the desired signal Trimpot A tiny potentiometer on a hearing aid (device) which allows the settings of the hearing aid (device) to be adjusted (using a screwdriver) TTY Telephone typewriter: a device which allows a hearing-impaired person to send text via an ordinary phone. The text can only be read by someone else with a TTY 16 © NSW DET 2008 Feedback to activities Activity 1 feedback 1. Which style of hearing aid (device) is least visible to others? CIC 2. Which style/s of hearing aid (device) is/are most reliable? BTE, Spectacle Aid, Body Aid 3. Which type/s of hearing aid (device) is/are easiest to clean? BTE, Spectacle Aid 4. Which type of hearing aid (device) is least sensitive to wind noise? CIC Activity 2 feedback Resource 2: Now that you’ve read this, name three ALDs which could be used for someone (with or without a hearing aid (device)) who has difficulty hearing on the phone: an amplified telephone a telephone coupler a sound-absorbing pad (eg foam rubber) Activity 3 feedback 1. Lady Catherine de Bourgh has a moderate sensorineural hearing loss but is no longer able to manage to insert a conventional hearing aid (device). Her audiometrist has tried ITEs and BTEs. What could she use instead? She could use a headphone ALD such as a binaural listener. 2. What options could you suggest to Mrs Profound to help her with the phone? Tick all that apply. (a) Suggest a different kind of hearing aid (device). (b) Give her information about the National Relay Service. (c) Give her training in using the telecoil on her hearing aid (device). (d) Give her information about Telephone Typewriters (TTY). (e) Suggest that she may consider a cochlear implant. (f) Suggest a volume-control phone. 17 © NSW DET 2008 Activity 4 feedback Resource 4: Having read this section of your textbook, draw the block diagrams for the following components next to their name. Microphone: Amplifier: Receiver: Activity 5 feedback 1. Which is correct? Tick the correct answer. Modern hearing aid (device) microphones: (a) create no noise of their own (b) are sensitive to vibrations (c) have a magnet and diaphragm (d) have a completely flat frequency response 2. The most efficient type of hearing aid (device) amplifier is the Class B. True or false? False. The Class D is the most efficient. 3. Hearing aid (device) receivers operate using: (a) electrical forces (b) pressure forces (c) astral forces (d) magnetic forces 4. Name the following filters: a. a filter that provides more gain to frequencies in a certain band: Band-pass filter b. a filter that allows more gain to high frequencies than low frequencies: High-pass filter (also known as a low-cut filter) 18 © NSW DET 2008 c. a filter that allows more gain to low frequencies than high frequencies: Low-pass filter (also known as a high-cut filter) 5. Hearing aid (device) telecoils pick up magnetic signals. True or false? True 6. Hearing aid (device) batteries last all year, just like watch batteries. True or false? False. Most batteries only last a week or two of consistent use. A hearing aid (device) draws current like a transistor radio, not like a watch. Activity 6 feedback 1. Write three key advantages of digital over analogue for hearing aids (devices). Digital aids (devices) can perform more complex processing. Digital aids (devices) can make decisions about how to process the sound. Digital aids (devices) are more efficient (in terms of size and power consumption) than analogue. 2. Write down the point Harvey Dillon makes regarding what digital aids (devices) can’t do: Digital aids (devices) do not provide ‘CD sound quality’. 19 © NSW DET 2008