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Converting dBnHL to dBHL

Carol Thomas Bryant, AuD

December 16, 2002


Question

1. What is the highest intensity level in dBnHL which can be used in ABR hearing threshold for deaf and normal patients.

2. How to convert dBnHL to dBHL.

Answer

1) The highest intensity level that can be reached in most commercially available ABR equipment is 90dBHL. Since it is the equipment limits that give us the 90dB intensity ceiling, when the maximum has been reached, it is independent of the person being tested or their auditory status.

Equipment companies may report higher output in their literature or in the calibration information section, around 130dB for instance. This can be misleading as the equipment has a built in correction that accounts for the amount of energy it takes to get from the internal board to the earphone, which is approximately 40dB.

2. How to convert dBnHL to dBHL.

To obtain a dBnHL value one can consult many published studies of normed data, The Handbook of Auditory Evoked Responses, by James Hall, PhD., is a good source. If one wishes to undertake the task themself, it is done by obtaining thresholds of normal hearing subjects typically at 1000Hz to correspond to the ABR click. The same subjects are administered a threshold ABR with a click stimulus. The comparison of the audiometric thresholds and the click ABR thresholds gives you the ''normed'' dB level.


Carol Thomas Bryant, Au.D.

Carol Thomas Bryant is the Manager of Training and Education for Madsen / GN Otometrics. She is responsible for developing advanced technology courses on behalf of Madsen as well as training programs for Madsen's full line of diagnostic instrumentation. Carol is Madsen's primary clinical interface for new U.S. products and software development.

Carol has spent the last ten years in the clinical environment, the last seven as Audiology Director for Tuscaloosa Ear Nose & Throat Center, P.C., in Tuscaloosa Alabama. She received her Au.D. from the University of Florida in Gainesville, her M.C.D. from Auburn University and completed graduate externships at Baylor College of Medicine in the Neurosensory Center of Methodist Hospital under the direction of Dr. James Jerger. Carol's background before entering Audiology was a B.S. in education and public school experience.


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carol thomas bryant

Carol Thomas Bryant, AuD