There are many different ways a hard-of-hearing person can use a telephone with their hearing aids. The three most common are:
(1) Holding the telephone near the microphone on the hearing aid.
(2) Using a telecoil (T-coil), holding the hearing aid against the phone, and
(3) Connecting the hearing aid to the telephone by means of Blue Tooth technology (usually through the remote control).
The techniques and engineering used in these three methods differ markedly. In this blog I am going to discuss only the T-coil method.
There is a substantial difference between the signal (magnetic flux output) created by landline telephones and cell phones. The T-coil technique works well with most landline phones, but not with most cell phones.
The manufacturing of conventional landline phones is regulated by laws, such as the Americans with Disabilities Act (ADA), that are designed to give people with hearing loss access to telecommunications. For many years, most landline telephones have been required to include a strong unshielded receiver in the handset that connects efficiently to a hearing aid.
In contrast, cell phones have tiny receivers with low magnetic flux output, i.e., a weak signal used to connect the phone and the hearing aid. This limits their effectiveness for people wearing hearing aids, although Federal Communication Commission regulations do require cell phone manufacturers to offer some models that are compatible with hearing aids.
Image from Hearing Loss Association of America, Albuquerque chapter, http://www.hlaabq.com/Telecoils.html.
HOW T-COILS WORK
Traditional landline telephones and most hearing aids have magnetic coils (small coils of wire built into the unit). To use a T-coil on a landline phone, the wearer switches the hearing aid to the “T” position and holds the phone against the hearing aid. Touching the phone to the aid allows the magnetic signal from the telephone to pass directly into the hearing aid. It is important to note that this is a magnetic connection, not an air-borne sound connection. Using a magnetic connection eliminates feedback from the signal.
It is important to stress the need to have the distance between the speaker in the telephone and the T-coil in the hearing aid very small—less than half an inch. Increasing this distance quickly destroys the magnetic signal.
PROGRAMMING A HEARING AID FOR T-COIL FUNCTION
The usual way to create special listening programs is first to create the basic (Universal) program. Then you open the Program Selection menu and select the program you want to generate–in this case T-coil.
When you use this approach, the computer-generated T-coil program usually has several major faults. That is because the amplified sound is far too complex.
The signal coming out of the telephone has already gone through compression, frequency modification, and clarity enhancement. You do not want to add “compression” or other high-tech features to a signal that has just been compressed. All you want the hearing aid to do is strengthen the telephone signal.
You do not want or need feedback reduction; since the phone signal is magnetic, there is no feedback loop. You also do not need automatic noise reduction, compression, output reduction, frequency transposition, or most other high-tech features. Such features become a hindrance when you run the telephone signal into the T-coil of the hearing aid.
However, you do need to pay careful attention to the frequency response (6 dB/octave or flat response is usually best) and gain, but you should turn most other features off. Therefore, for the telecoil program, reduce the AGC to the minimum and turn off frequency transposition. You can also turn off digital feedback reduction as long as you are using a pure “T” input (i.e., the microphones are turned off).
Check to make sure your settings are appropriate by using a listening scope (attached to the hearing aid), setting the instrument to T, and listening to a landline phone call. If it sounds loud and clear to you, it will probably sound loud and clear to your patient.
AudioScan real ear equipment has a quick “Speechmap for Telecoil” test built in to the Verifit and Verifit 2 systems. Besides testing that the telecoil response matches the mic response (a 1 minute test) it will allow providers to quickly verify if the telecoil is vertically oriented in the hearing aid.
Hearing loop fields – in the seated area – involve a vertical magnetic field. In all loops there are areas where the field has a large horizontal component: this happens on the outer margins/side of the loop and above the wire. In those areas users of some Cochlear America’s implants and Starkey devices which are unfortunately equipped with horizontal telecoils, can still pick up the loop signal. Of course it is much easier for the consumer to vary the orientation of a phone held closely near a hearing aid (i.e. find the “hotspot” if their instrument offers a vertical telecoil) than it is for the user of horizontal telecoil to sit in a hearing loop having to look at the floor or holding one’s head sideways – preventing the listener in a looped lecture to see the speaker but allowing him or her to hear the speaker. Most audiologists think that offering a telecoil is enough and are thrown for a loop (pun intended) if the consumer complains about having to hold their head a certain way in a loop to hear. MFRs need to be very clear about their product and their telecoils.
Manufacturers would do well to start providing the SPLITS (optimal telecoil response in a hearing aid) as well as the SPLIV (“as worn on the ear” telecoil) specs as is mandated in the new S3.22 ANSI standard which, unfortunately, will likely take years for the FDA to approve. I would applaud if they would also spend 5 or 10 minutes in their CEU classes on their particular product telecoils orientation and proper programming.
Contrary to widely held misconception among some audiologists, telecoils do have broad frequency responses well into the 5000+Hz range and match the broad frequency response offered in an IEC standard hearing loop of 100-5000 Hz. This means that telecoils used in loops provide unparalleled speech understanding and contribute to consumer satisfaction with their hearing devices in places where hearing aids alone are unable to deliver.
1. http://www.hearingreview.com/2014/09/consumer-perceptions-impact-inductively-looped-venues-utility-hearing-devices/
2. http://www.audiologypractices.org/used-alone-hearing-aids-fail-to-deliver
3. http://www.audiologyonline.com/articles/telecoil-lonely-transducer-that-big-11911
Juliette Excellent explanation and information to assist audiologists, manufacturers of hearing devices and consumers wearing these devices on the best use as well as telecoil orientation
Cellphones have a T rating and makes a big difference in performance. Ideally consumers should look for a T rating of T3 or T4 for use with telecoil. See this link for further info: http://www.asha.org/public/hearing/Hearing-Aids-and-Cell-Phones/
This post seems to perpetuate the belief among many hearing care professionals that the t-coil’s primary use is with the telephone. In my experience that application is of secondary importance to a huge segment of telecoil users.
With volume controls, tone controls. neck loop jacks, text and more, fewer people need to engage their telecoils for use with the ear piece on their telephone. This, in turn, negates the supposed benefit of automatic telecoil activation that, without a manual over ride, makes the telecoils unable to function in a looped environment. Telecoil users today have a fast growing list of opportunities to use that feature on their hearing aids in churches, theaters, meeting rooms, legislative chambers and even in their home TV room – something not alluded to in this piece.
Thank you, Juliette, for detailing some of the aspect of hearing loop technology and the problems that can be encountered with telecoil use in a looped environment.
T-Coils are also the link to Hearing Loops. We are pleased to note the increased use of Hearing Loops in public venues such as houses of worship and other places; concert halls, playhouses, city council chambers, transportation terminals (airports and rail) community centers and countless other venues. Hearing Loop initiatives are alive and well in Southern CA with over 100 new sites having been “Looped” in the last 24 months and countless more awaiting funding for new “Loop” installations. Hearing Now USA is leading the movement for increased use of Hearing Loops in public places that use amplified sound, as well as banks, pharmacies, ticket windows and other sites that are frequented by the hearing impaired.
I have Phonak hearing aids with tcoil. When I go to theater that give you a neck loop with receiver they do not work. If the theater is wired they do work. What do I need to correct this problem?