What can be done to improve speech intelligibility on the phone?
Several factors contribute to hearing aid user’s experienced difficulties communicating on the phone. These include the absence of visual cues, inappropriate or inadequate coupling to the phone, presence of background noise and acoustic feedback. Success on the phone should be a priority for the hearing care specialist, as phone use is linked to self-reported quality of life.
To ensure that the phone being used will work well with hearing aids, it is important to understand the modes in which the hearing aids operate. Hearing aids operate in one of two modes – acoustic coupling or Telecoil (inductive) coupling. Hearing aids operating in acoustic coupling mode (holding the phone receiver to the hearing aid microphone) receive and amplify all sounds surrounding the user. Sounds amplified in this mode include desired sounds, such as a telephone's audio signal, as well as unwanted ambient noise. Hearing aids operating in Telecoil coupling mode (about 60 percent of hearing aids contain Telecoils) receive signals from magnetic fields generated by Telecoil-compatible telephones. Amplification of unwanted ambient noise can be avoided in this mode by turning off the hearing aid microphones in the Telecoil program. Turning off the hearing aid microphones also eliminates the issue of feedback squeal, an issue often associated with acoustic coupling. The use of a Telecoil hearing aid program translates to approximately a 6dB improvement in SRT score when compared to acoustic coupling.
Not all phones are created equal when it comes to use in combination with hearing aids. Generally speaking, analog telephones do not pose a risk of interference and will work well with most hearing aid models. But with most phones, both landline and cellular, being digital these days there is a risk of interference caused by electromagnetic energy emitted by the telephone's antenna, backlight or other components. An American National Standard Institute (ANSI) standard exists for the compatibility of phones and hearing aids. The standard offers a rating system that the clinician and end user can use as guidance. A telephone handset is considered hearing aid compatible for Telecoil coupling if it meets a T3 rating. In addition to rating the phones, the ANSI standard also provides ratings for hearing aids from M1 to M4. On that rating scale a rating of M1 signifies the least immune to RF interference and M4 the most immune. To find out is a particular telephone is likely to interfere with a particular hearing aid, the rating of the hearing aid is added to the rating of the telephone. A sum of five indicates that the telephone would provide normal use and a sum of six or greater indicates that the telephone will provide excellent performance with that specific hearing aid.
The quality of the signal received by the hearing aid user will also be reliant on the placement of the receiver. It is worthwhile to practice phone placement with your patients as most do not find it intuitive to place the receiver slightly behind and above the ear (ensuring that the hearing aid microphone or Telecoil is in close proximity to the telephone receiver). Most manufacturers offer the option to stream telephone conversations from Bluetooth enabled phones to the hearing aids. This removes the reliance on correct receiver placement and offers the possibility to listen to the phone conversation in both ears. Wireless streamed sound offers a 10 to 18dB improvement in SRT score, variation in wireless benefit is dependent on the technology used with the greatest benefit measured using Made For iPhone (MFi) technology where the phone signal is streamed directly to the hearing aids without the use of an intermediary device.
Most of the patients we see make use of cell phones. Cell phones offer several advantages for the hard of hearing; speaker phone, volume control and vibrating ringer are standard in most models. Some cell phones are optimized for Telecoil compatibility and most models offer Bluetooth. Cell phones can also be used to send and receive text messages and Apps can be purchased that enable captioned phone calls. Several landline phones designed specifically for the hard of hearing are available on the market. These are designed to boost high frequencies (usually a 30 to 40dB boost) and feature frequency and loudness adjustable ringers.