Infrared has the specific advantage that the signal does not cross walls and hence provides a very high level of confidentiality. It can also be used in multi-channel systems for simultaneous translation, where it is used purely as a communications system.
It suffers quite badly from shadowing, offering many situations in rooms where the signal is lost. Special receivers have to be issued which draw attention to the hearing disability. There are also very serious concerns about the standards of hygiene; have the receivers really been cleaned and disinfected? The cost of these processes is a significant expenditure for the operator of the facility.
Radio systems are even less attractive. Apart from the negative user response noted above, there is a major problem with signal loss. Professional radio microphones use diversity reception to reduce signal loss due to reflection of the radio signals from walls, etc.. This is not possible with the radio receivers used for assistive listening. Furthermore, there is a major problem with shortage of frequencies and confidentiality is totally non-existent.
In comparison, induction loops have the following advantages:
- Uses built-in T coil in hearing aid
- Utilises internal tonal correction
- No additional receiver needed
- Hygiene problems eliminated
- No loss of special receivers from venues
- Will work in conditions of bright light and outside
Sadly, not all hearing aids are fitted with the loop facility. In the UK, almost all NHS aids are equipped with a ‘T’ position, as are many privately sold aids. In the UK private sector, it is often the audiologist who decides whether to offer the loop reception facility, but generally they do offer aids with a ‘T’ setting. At present, about 95% of hearing aids in the UK are said to have the loop receiving function.
In the USA, audiologists do acknowledge the benefit of the ‘T’ facility, however up to 50% of aids sold in the USA are without the ‘T’ coil facility.
Digital hearing aids work in exactly the same way as ordinary analogue aids in terms of induction loop use but you must make sure that the digital hearing aid has a ‘T’ switch position. As far as we are aware, all digital hearing aids supplied by the NHS (National Health Service) in the UK have a ‘T’ coil facility. Privately dispensed digital aids may or may not have a ‘T’ coil. As policies over ‘T’ coil provision in hearing aids vary around the world – check with your audiologist about this before you buy, as it may affect what they offer to you. Many digital hearing aids allow the option of setting the relative levels between microphone and ‘T’ coil inputs to be adjusted by the audiologist. If the loop signal is quiet / loud relative to normal microphone use, ask your audiologist to adjust it for you.
The international standard governing the use of induction loops (IEC60118-4) requires that the loop coil be vertically orientated to pick up the magnetic signal. Regretably, IEC60118-1 which applies to hearing aids, does not define any orientation. Some hearing aids are available with a pick up coil adjusted for reception of horizontal magnetic fields and these may give poor results even when used in a correctly installed loop system unless you bow your head forwards to face the floor. Ampetronic are currently researching this effect and would welcome your comments if you have experienced this problem. Please let us know the hearing aid manufacturer, model number and date of purchase for our records together with a brief description of the exact circumstances under which the problem arose.
Always check with your audiologist BEFORE purchasing a hearing aid to ensure compatibility with induction loop systems.
There has never been a technical study on whether a hearing loop could have any negative effect on a pacemaker or interfere with its operation.
Studies have reached the ‘Proposal’ stage before but have been rejected by the experts as the magnetic field strength produced by a hearing loop system could not in all practical reality affect a pacemaker, and so the study would be rendered pointless.
However the concern is understandable and it is a sensible question considering how a pacemaker functions.
Although there is no evidence to state that the magnetic field produced by a hearing loop can effect a pacemaker, in order to alleviate any doubt Ampetronic simply suggest that a distance of 150mm or 6’’ separation between loop cable and pacemaker is maintained.
This would imply that a neck loop is not placed directly across the chest and that a person with a pacemaker should not lean against a counter or portable loop system”.
Automatic Gain Control is standard in all Ampetronic equipment. AGC automatically adjusts the output level of a loop amplifier to retain a constant level while retaining normal dynamics of speech and music. AGC provides a dynamic range that can be comfortably received by the hearing aid, and provides excellent intelligibility for the hearing aid wearer over a wide range of input levels.
AGC is a fundamental part of creating an assistive listening system that is beneficial to the hearing impaired. The international standard for induction loop systems IEC60118-4 does not mandate the use of AGC, however it is practically not possible in normal circumstances to meet the requirements of this standard without gain control.
An Induction Loop, also known as a Hearing Loop or T-Loop, is an assistive listening system that provides access to facilities for those with a hearing impairment. It takes a sound source and transfers it directly to a hearing aid via a magnetic field without background noise interference or distortion.
The presence of an Induction Loop should always be indicated by the internationally recognised hearing impaired sign with a T symbol.
Over the last 25 years Hearing Loops have become the default assistive listening solution in Europe, Scandinavia and Australasia, and are now becoming increasing prevalent in America. Due to their benefits and ease of use, hard of hearing groups are mandating their installation in locations as diverse as taxis, kiosks, schools, houses of worship, concert halls and stadiums.
Hearing aids enhance sound in close conversational settings, or where there is little background noise or distance to the source. Many modern digital hearing aids can filter out a great deal of background noise, however this does not resolve the issue of distance between the sound source and the hearing aid user.
A Hearing Loop magnetically transfers the sound from a microphone, TV or audio signal directly to hearing aids and cochlear implants without interference, background noise or distortion, regardless of distance.
The cost of a Hearing Loop system is proportional to the size and complexity of the loop design, the associated amplifier(s) and the accessories required.
A ‘fit-for-purpose’ retail/reception desk or home TV room loop should typically be less than £300 plus any installation fees, whereas a professional system for a large venue may cost thousands of pounds proportional to the size of the venue and other audio visual equipment that may be installed.
It is worth remembering that the cost of installing a Hearing Loop in a medium size venue, such as a place of worship, will often be less than the cost a single user has paid for their professionally fitted hearing aids.
The increasing popularity of Hearing Loops has seen a steady increase in the inclusion of telecoils in hearing aids. At present just under 70% of hearing aid models in active use are fitted with them.
This number is as high as 95% in countries where Hearing Loops are already established.
All new model cochlear implants now offer telecoils with manufactures stating that 95% of all new hearing aids are to offer telecoils, although some Audiologists do not activate them as standard, especially in the United States.
Hearing aids usually have an active life of around 5 to 10 years before a person’s hearing degeneration dictates a replacement. It is therefore reasonable to assume that by 2020 almost all hearing aids will have a telecoil installed.
If you would like more information about your model of hearing aids please contact your Audiologist.
All assistive listening systems, including hearing/induction loops, can be used with portable receivers and headsets.
Wireless technologies are not suitable for assistive listening solutions that directly utilise the hearing aid in their current form as they cause significant battery drain and have a limited range.
In the case of Bluetooth, as an example, the area cover is between 5-100 square meters (depending on type), the technology can only support the connection of up to 7 users at the same time and also requires the ‘pairing’ of devices in order to connect them.
Although Hearing Loops have traditionally been used in places such as houses worship and conference rooms, advances in technology have allowed the spread of the technology to areas including:
Stadiums, theatres, cinemas, concert halls, sports halls, courts, lecture halls, school classrooms, video conferencing suites, meeting rooms, museum exhibits, fairground rides, taxis, help points, nursing homes, domestic TV rooms, retail counters, receptions, transport stations, waiting rooms, boats, minibuses, cars and trains.
The way an Induction Loop (otherwise known as Hearing Loop or T-Loop) works is quite simple:
A sound source, such as a voice, TV, cinema sound system or other audio system is captured using a microphone or via a line out connection.
The sound signal is then connected to an Audio Induction Loop Amplifier which generates a current to pass the signal to an induction loop, usually made of copper tape or wire.
The copper wire induction loop surrounds the area where the listening audience is located and produces a magnetic field.
The magnetic field is picked up by the Telecoil (or T-coil) inside the hearing aid of hearing impaired members of the audience.
The hearing aid tailors the sound to the specific needs of the individual. Sound is delivered directly into the ear canal, without background noise and with the full spectrum of sound frequencies required for intelligibility.
The number of users who can benefit from the system at one time is only limited by the number of people that can fit in the ‘looped’ area. Expensive receivers are not required and users don’t suffer the inconvenience of asking for and wearing a headset that marks them out as hard of hearing.
Hearing Loops are an inherently simple technology, but care should be taken (and professional advise sought) in their design, specification and installation so that the facility conforms to the International Standard and is of optimum benefit to the end user.
For more information see How Induction Loops Work
Many freestanding induction loop products (or ‘portable’ loops) are for sale in the UK and around the world, promoted for a host of benefits and applications. Freestanding loops certainly have their place, however if you plan to specify or purchase one of these units – for any application – we encourage you to think through a few important factors that determine whether it is the right solution for you, and most importantly : Will the Induction Loop System provide a real benefit to the hard-of-hearing?
To meet the requirements of disability access legislation, and to make sure that your investment in Induction Loop technology is really helping to make a difference, you must make sure that there is a real benefit for the end user. An induction loop will provide a benefit only if the system provides the end user with better separation of the wanted signal (usually a voice) from the background noise than the hearing aid can achieve on it’s own. We need to achieve a clear and intelligible sound reproduction. For a freestanding loop it is therefore vital to ask a few questions:
Will the microphone pick up what is required and nothing more?
The microphone must be directional and pointed at the source (often the person speaking) – an omni-directional microphone will pick up noise from all directions, therefore collecting all background noise as well! If there is more that one person speaking, a single microphone is unlikely to be adequate, so many freestanding systems will not be suitable – for example in a meeting room with several people, a carefully designed audio system is vital if the system is going to be of any benefit.
Is there a built-in microphone that limits where the unit can be located?
A built in microphone will force the freestanding unit to be placed in a specific position relative to the speaker. This may not be ideal for either the layout of the counter or desk, and may not be compatible with getting the magnetic field in the right place for the hearing aid user. Built in microphones can make this configuration very difficult or impossible to get right.
Is the sound quality clear and intelligible?
Due to the pressure to keep costs to a minimum, unfortunately many freestanding loop manufacturers have decided to compromise on sound quality to cut costs. It is simple to make an induction loop with low output at the higher frequencies which are vital for the hard-of-hearing to hear clearly, resulting in a muffled sound. A good system must have a flat frequency response over the audio spectrum, +/- 3dB from 100 Hz to 5 kHz. This is specified in an international standard (IEC 60118-4). Does the specification clearly state this? If not, you should be aware that the unit is unlikely to provide a benefit to the user, and is more likely to be a source of upset and frustration – as well as failing to meet the international standards!
Is the signal produced by the loop in the right place for the user?
Induction loops are ruled by some very basic principles. One of these is that the magnetic field in the user space that a loop creates is more and more variable and more constrained the smaller the loop becomes. There is no magic solution, a small loop might be more attractive for your counter-top, but it means much more difficulty for the user to make sure that they are standing, bending, crouching, leaning or tilting themselves just right to get in a good spot to hear the signal clearly. Many users do not understand this problem. Choosing a small loop size is a major compromise to performance, so make sure that you are doing this for very good reasons – a larger loop may need a slightly more complex installation, but the performance is dramatically better for the user. Ask the supplier about the shape of field that the unit produces – there are always ‘dead’ spots around the loop where there is no signal, so you must be aware of where they are to make sure the unit is positioned effectively. The highly variable pattern produced by freestanding loops is all too often not understood even by the manufacturers, so make sure that you get a clear answer before you agree to buy!
Will the freestanding unit get in the way? And what happens if it gets moved?
The counter, desk or other space on which you are considering placing your freestanding loop is no doubt used for a lot of other reasons too. Can you permanently locate the loop somewhere so that it points towards the user (this is essential for a good signal whatever you might be told!) and also ensure that the microphone points towards the sound source? If it is going to be knocked, moved or put away, the benefit to the user is likely to be lost completely. Don’t expect the hard-of-hearing user to know how to make it work, they will often just assume the system doesn’t work properly or isn’t turned on. If the loop is to be a benefit for the end user, you must ensure that it is fixed permanently in position.
Batteries or mains power?
Some freestanding units are designed to run off rechargeable batteries. This can create a major headache for the people running the service area where the loops are used. If such a loop is kept on a charger, it often will not be where it needs to be when a hard-of-hearing user needs it. If the loop is kept on a counter, it is not charging up, so it will either be switched off to conserve power, or very often will run out of power. The people responsible for managing the loops are very unlikely to be able to tell if the loop system is working properly or not without special test equipment – you are only going to find out when a hard-of-hearing person arrives and can not get any benefit from your system, and only if they let you know. Furthermore, suitable training needs to be provided to ensure that all the staff dealing with clients know how to use and position the loop system. Loop systems should be permanently on and operating at all times if they are going to be a benefit unless there is absolutely no other choice available.
Can a portable system be available ‘on demand’ just when it is needed?
Requiring a hard-of-hearing individual to ask for help is not acceptable if it can be avoided and is against much disability access legislation, and discriminates against the disabled. For those lucky enough to suffer from no disability it may not be so obvious why the hard-of-hearing should not have to ask. However a system which is only available ‘on-demand’ requires the hard-of-hearing person to declare themselves as disabled, and cause what they may well see as disruption or hassle. Such an arrangement can cause discomfort or embarrassment and is likely to result in the systems that you have invested in never being used, and providing no benefit at all to the users. A truly beneficial induction loop system should always be working away unseen and without attention, providing help to those that need it whenever they need it. Unfortunately there are some portable loop systems used ‘on-demand’, whether to cut costs or through a misunderstanding of how to provide fair access for the disabled community. Whether your investment in loop systems is to provide a benefit to the hard-of-hearing, or just to meet legislation, make sure that your system is always available or you will be discriminating against those you are trying to help.
A Phased Array is a used to counter the effect of metal structures, or to achieve even field strength over large areas.
A series of loop rectangles laid in a specific method, with a second array laid over the top. The two arrays are driven with an amplifier capable of driving current through two separate loops simultaneously with one loop shifted 90 degrees out of phase with the other, or two amplifiers connected together connected by a phase shifter.
If designed carefully the result is an astonishingly even field coverage over a practically unlimited size of room, in the presence of metal or not. Overspill will be reduced from a perimeter loop substantially, but will still radiate up to 1 room width from the side of the room.
A Phased Array requires careful design to achieve even coverage. Ampetronic can carry out this design for you, check your designs for free, or offer you training or advice for designing your own arrays.
Current Drive in Induction Loop Amplifiers
As explained elsewhere, the basic principle of an Induction Loop system is that an electrical current through the wire creates a magnetic field which is picked up by the hearing aid. There is an International standard (IEC 60118-4), which establishes the intensity of the magnetic field, and the frequency response needed from the system. This specifies that over the range from 100 Hz to 5 kHz, the signal will be within the limits of ± 3dB relative to the signal at 1 kHz.
A significant amount of research has also shown that speech, in the short term where intelligibility is crucial, requires that the system must handle full power signals up to at least 1600 Hz.
Loop systems have as a fundamental aspect, the fact that a definite length of cable is used. Some designers and contractors ignore the fact that this wire length has a definitive inductance. This component is of such magnitude that audio signals are affected. The use of multiple turn loops has a very serious effect, because the impedance of this inductive component increase by the square of the number of turns in the loop, while the signal strength increase only by the number of turns, for the same current. As the impedance of the loop, due to this inductance, increases with frequency, the serious problem arises that when the loop is driven by an amplifier designed for driving loudspeakers at good quality, the output current when connected to the loop reduced significantly with frequency.
The table below gives the frequency at which the response is down by 3 dB relative to reference, and this problem cannot be resolved easily by simple “Tone Controls” . The table also indicates clearly the immense loss created by multi-tun loops in such a situation. The mathematical basis for the table is simply the ratio between resistance of the loop, giving the base current when driven by an amplifier designed for good loudspeaker damping (low internal impedance), and the magnitude of the loop impedance, made up from both resistance and inductance.
As shown clearly, the frequency response requirements of the standard simply cannot be met.
|Cable section (mm²)||Single Turn Loop (Hz)||2-Turn Loop (Hz)||3-Turn Loop (Hz)|
|Cable Section AWG||Single Turn Loop (Hz)||2-Turn Loop (Hz)||3-Turn Loop (Hz)|
Using Constant Current feed removes the problem, as the special loop drivers as designed by Ampetronic control the current into the loop independent of the loop impedance. While there are limitations of cable length etc., as referred to elsewhere, the Ampetronic drivers easily offer the required frequency response.
The magnetic field produced by a standard Hearing Loop design is not limited to the inside of the loop and can ‘spill’ into adjacent areas. A standard perimeter loop can ‘spill’ up to 3 times the diameter of the loop, both horizontally and vertically.
This causes interference with loops close by and can also lead to security issues with regard to confidentiality.
Modern computer aided Loop designs can prevent this by designing systems that use multiple loops and amplifiers to create what is known as a ‘low spill’ system that doesn’t extend more than a few feet from the edge of the loop.
In some extreme cases, the environment may contain a significant amount of cabling or high voltage electricity that creates its own magnetic field, which causes interference making an Induction Loop either uneconomical or unsuitable.
However, with the use of modern equipment and the correct design, these cases are now very limited and a simple test can be carried out to identify any issues using a Field Strength Meter.
Hearing Loop Systems are typically more expensive and time consuming to install than other assistive listening systems, however this cost is usually recouped over time as the systems are ‘fit and forget’ meaning that they require little maintenance and operation.
Room Hearing Loops consist of two main components that are required for installation, the amplifier and the loop. The amplifier can either be placed in a rack with other audio visual equipment, or mounted to a wall in smaller venues.
The loop itself is usually installed under carpets or wooden flooring and occasionally on architrave or in the ceiling.
Small reception, or desk mounted loops are simpler as the loop often comes ready constructed for attachment.
In many cases it is possible to lay copper wire or tape around the edge of a room to form what is referred to as a ‘perimeter loop’, or sometimes even bury the cable in the floor outside the building.
However this is often not the case as factors such as room size , shape, building construction and metal within nearby structures can all prevent a perimeter loop from being a feasible choice.
Specialised computer programs now exist than can design a loop pattern comprised of many smaller loops, and sometimes more than one amplifier, which create a magnetic field that will operate to International Standards of conformity for field strength, background noise and frequency range.
Please seek the advice of a qualified specifier before installing a system. Remember, if it is not providing a genuine benefit to the hearing impaired and conforming to the International Standard for performance (IEC 60118-4), then it isn’t working.
Although the installation of a Hearing Loop (or Induction Loop) can be done by anyone with basic electrical knowledge, a field strength meter and certification documentation is required to test and commission the system to ensure it is working to the International Standard required by the user.
If you do not have a field strength meter, or are unsure about how to fulfil the requirements of the standard it is recommended that a qualified installer is used – remember, if the Hearing Loop isn’t working to the international Standard, then it isn’t working.