There are different techniques available to the Audiologist:-
Real ear measurement
This is an objective method of determining how well matched the frequency response of the hearing aid is to your hearing loss with the hearing aid actually in the ear, as it would normally be used. A thin measuring tube is placed behind the hearing aid in the ear canal and this enables the sound delivered to the eardrum to be accurately measured. To make the measurement more real, normal speech is used for the measurement. The measurement is then compared to the response (target) that international research has shown to be best for your type of hearing loss. I use targets proposed by NAL (National Acoustics Lab) and the latest is NAL NL2.
This is the technique that I routinely use for re-assessing hearing aids and during the initial fitting proceedure. Real ear measurement can be used with the hearing aid connected to its programming software so that it can be adjusted (fine-tuned) accurately to your hearing loss.
Coupler measurements
This is an objective method of determining how well matched the frequency response of the hearing aid is to your hearing loss with the hearing aid out of the ear. The hearing aid is placed in a ‘coupler’ to the measuring equipment. This coupler mimics the acoustics of an average ear canal (usually 2cc). The hearing aid can then be adjusted.
2cc coupler measurements are not as accurate as real ear measurements unless the difference between the real ear and coupler are known. If so, accurate fine-tuning is possible. This technique is useful if the patient is not present or is uncooperative (young children).
Speech mapping
This technique provides a real-time visual display of the hearing aid output which can be compared to targets. it is best used with a probe tube in the ear canal, behind the hearing aid, similar to real ear measurements. This technique allows the variation in loudness of different frequencies of speech to be assessed in real time. The hearing aid can then be adjusted and the resultant affects measured.