The National Acoustic Laboratories (NAL) hearing aid fitting formulas are a set of algorithms that are used to prescribe hearing aids based on an individual’s unique hearing profile. These formulas were developed through extensive research on the relationship between hearing loss and the benefit that can be obtained from amplification.
The NAL fitting formulas are based on the results of numerous studies on hearing loss and hearing aid benefit, including both laboratory and field studies. The research has involved the measurement of hearing thresholds, the assessment of speech recognition abilities in quiet and in noise, and the evaluation of listening effort and overall satisfaction with amplification.
The NAL fitting formulas take into account factors such as the degree and type of hearing loss, the individual’s age, and the individual’s listening needs and preferences. The formulas are used to calculate the appropriate settings for a hearing aid based on the results of a hearing test, and the resulting settings are intended to provide the most natural and effective amplification for the wearer.
Overall, the research behind the NAL fitting formulas has helped to establish a scientific foundation for the prescription of hearing aids and has contributed to the development of evidence-based practice guidelines for hearing healthcare professionals.
National Acoustic Laboratories. (n.d.). NAL-NL1. Retrieved from https://www.hearing.edu.au/our-research/national-acoustic-laboratories/nal-fitting-formulas
Moore, B. C. J., & Stone, M. A. (2016). The NAL-NL2: A review of the current prescription formula for hearing aids. Trends in Amplification, 20(4), 185-193.