CROS stands for Contralateral Routing Of Sound. In simple words, it means a device that transfers signals received on one ear to the other ear.
If you got one ear that is totally deaf (meaning, there is no use putting a hearing aid on it) and your other ear is OK, or close to that, you can use CROS. CROS hearing aids gets the sounds from the deaf ear to the good ear.
They put a special hearing aid on the deaf
ear (It looks just like a regular hearing aid). This device gets the
sounds from the surrounding and transmits it to the device on the good
ear (This one also looks like a regular hearing aid).
The device on the “good” ear, is a receiver and an amplifier. It receives the signals from the first device (the one on the deaf ear). Then, it sends the amplified voices to the ear canal, just like on a standard hearing aid.
Generally speaking, it looks just like two hearing aids, but they got different functionalities. The devices must be either BTE-like or ITE-like and the earmold must be open fit so it won’t block sounds that the good ear can hear from the first place. There is only an earmold on the good ear, the device on the deaf ear just receives the sounds.
Bi CROS hearing aids is in use when the better ear is also with some hearing loss. In this case, the signals from the deaf ear are transmitted to your better ear, and then they are being amplified. In addition, It functions as a standard hearing aid for the better ear. In standard CROS you don’t have to amplify the sounds since the better ear is totally functioning. If you got a bi-CROS, the device on the better ear also functions as a regular hearing aid.
If your hearing ear is in good shape, there is no need to
amplify the signals from the deaf ear. Moreover, the microphone is on
the deaf ear and the speaker is on the good ear, so there really
shouldn’t be any feedback issues.
If you use Bi-CROS, there is a higher potential for feedback. That’s because the signals are amplified. On the other hand, the earmold doesn’t have to be open fit.You can use a sealed earmold and this should save you the feedback noises.
Sounds from the deaf side don't get lost. You can hear them on your good ear.
You can still have some localization of voices (It’s the ability to figure out where the sounds are coming from). It depends on getting sounds from both sides of the head. CROS isn’t a perfect solution but it’s better than nothing.
In some cases, the sound from the death ear can disturb, since it blends with the sounds that you normally receive on the good ear.
Some abilities that require both your ears might be harmed. Things like localization and noise reduction.
BAHA is the main “competitor” of CROS. It can also be helpful if you got a significant hearing loss on one side only. BAHA requires a surgery and it got it’s own problems and benefits.
The signals from the death ear to the good ear are transferred
in two ways. The first option is a wire that runs on the back of the
neck. The other option is using RF signals. In this case, the
communication between the ears is done wireless.
CROS can be extremely useful if people address you mostly to your deaf side. Think of buss drivers with hearing loss on his right ear. Not only that people talk to his deaf side, he also got the street noise on his hearing side...