The CRM-220 radio aid system - what is it?

Principal of operation

The CRM-220 is a wireless communication system specifically for use by people with a hearing loss. The system consists of two main elements: a transmitter and a receiver. The transmitter unit collects the sound and transmits it without loss of quality to a receiving unit. Both ‘ends’ of the system are portable and the receiving unit presents this relayed sound in some way to the user’s hearing aids.

Design objectives

When originally designing the Connevans CRM-220 radio aid, one major design objective was to provide a unit which makes use of the individually tailored response of the user’s own hearing aid, with good sound quality, yet being robust with straight forward operation.

Now several years later, the CRM-220 system is a tried and tested, good value system for hearing aid users.

What will a radio aid system NOT do?

Well, a radio aid system adds no gain (or power or volume) to a hearing aid - so a user will not be given increased amplification. It is the power output of the hearing aid, NOT the radio aid, that the hearing aid user listens to.

It would however be acceptable to say that a radio aid system adds 'effective' gain because as a speaker moves away from arm’s length distance from a hearing aid user there is no reduction in the volume (or power!) presented to them.

What does it do then?

The Connevans CRM-220 radio aid system will provide a consistent sound feed over varying distances just as if the person speaking was always at arm’s length.

Who wears what?

The radio transmitter unit is worn by the person speaking. The radio receiver is worn by the hearing aid user who carries it around with them wherever they go.

When using the radio aid system the users still listen to their own hearing aids but now the speaker's voice is fed ‘directly to the ear of the hearing aid user’.

How does the hearing aid ‘hear’ the radio microphone?

The input to the user’s aid from the radio microphone receiver can be a direct connection (if available) or via the inductive loop pick-up (T) coil.

The radio aid system will provide a consistent level of sound wherever the hearing aid user or person talking may be in the room. There is a great improvement in the perceived ‘signal to noise ratio’ heard by the hearing aid user with less background ‘mush’. The system will give a range of at least a room inside or coverage outside over a football pitch, thus meeting most requirements.

What happens if the person speaking talks loudly?

The Connevans radio microphone CRM-220 System has an automatic gain control to prevent loud sounds from causing discomfort or distortion.

How well does it work?

The CRM-220 has a good frequency response with low levels of distortion. The overall performance of the system will be limited by the user’s own aids - if the aids are correctly fitted then the radio aid system will perform well, but if the hearing aids are badly chosen, it will not perform well.

Who will the CRM-220 help?

Your audiologist is the best person to consult with regards to suitability of equipment; however, as a rough guide a CRM-220 radio aid system will be of benefit to anyone who is a good hearing aid user. If you are able to sit beside a hearing aid user in a quiet room and communicate via their hearing aids rather than by lip reading (i.e. actually able to use their hearing aids) then a radio aid system will probably be helpful, allowing the hearing aid user to ‘listen at a distance’. The CRM-220 radio microphone will help to counteract the problems of distracting sounds outside that quiet room situation.

How does it sound?

Using a stetofork listening stick it is possible for a hearing person to ‘get a feel’ for the improvement that a CRM-220 radio microphone can give in different noisy situations. When demonstrating a CRM-220 to a user sitting nearby, an initial response from the hearing aid user of 'sounds the same', is not unusual. It is difficult to improve on the hearing aids themselves and because a consultation room is usually quiet it is not until we move outside into a more usual level of ambient noise with a greater distance from the person talking that the user realises the potential benefit of a radio microphone aid system.

Bear in mind however, that a hearing aid user is not used to interpreting sounds from afar. 'Over here' means nothing, people often don’t understand at first where the sound comes from if they cannot see the speaker talking. A radio aid increases the emphasis on sound, but visual clues are still important. Experience and practice are necessary to make full use of this available 'sound'.

Is the CRM-220 a true wireless radio system?

Yes. The Connevans CRM-220 is an FM radio system working on a similar basis to the domestic BBC VHF radio network, although the CRM-220 radio microphone operates at a higher frequency and cannot be picked up on a conventional domestic radio. BBC Radio 2 transmits between 88-90.2 MHz in the VHF FM band; the radio microphone systems for hearing impaired people operate around 173-175 MHz band. In order that a number of CRM-220 radio microphone systems may operate on the same site, a number of channels have been allocated, each with specific frequencies. Manufacturers use varying channel coding systems; Connevans uses a channel number system.

Who manufactures the CRM-220?

The CRM-220 equipment has been designed by Connevans and is manufactured, sold and serviced in our works in Reigate - Made in Britain.

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