Question
I obtain LDL measurements (loud but ok) using both speech and pure tones. The instructions are the same for both procedures. More often than not the patient has an LDL of 100 dB or so for pure tones but only 75 or 80dB for speech. I'm assuming this is the binaural fusion effect for speech. Should I use speech rather than tones for this measurement?Answer
Obtaining LDL (loudness discomfort level) or UCL (uncomfortable level) measurements is a recommended step in assessing a person's residual dynamic range to help appropriately set the OSPL90 (output sound pressure level) or MPO (maximum power output) of hearing instruments. Dynamic range is defined as the level of difference between a person's threshold of audibility and discomfort. Before multichannel hearing instruments, it was not as critical to measure frequency-specific LDLs because not enough adjustment could be made to account for frequency-specific differences. With today's hearing instruments incorporating as many as ten to twenty channels, conducting frequency-specific pure tone LDL testing is necessary to better appropriately map a person's dynamic range in an effort to more accurately set the MPO of the hearing instruments.
I recommend using frequency-specific information for setting the proper MPO because speech is a broadband stimulus encompassing many frequencies. It is important to convert the hearing level LDLs derived from audiometric testing into SPL so it corresponds with the hearing instrument(s) specifications. Because there are volumetric differences between the real ear (RE) and that of a coupler (C), you should factor in a real ear to coupler difference (RECD). Once the LDL measurements are calculated into the MPO settings of the hearing instruments, you can present speech (or other broadband stimuli) to evaluate the perceived loudness of high intensity sounds as amplified through the hearing instruments. This will help ensure all inputs through the hearing instrument(s) will be below the LDL.
Side note: The reason that you were seeing a lower LDL for speech compared to pure tones (assuming you were testing under earphones monaurally) was due to loudness summation of the speech signal. There was more energy across multiple frequencies for the speech signal versus the energy presented at a single frequency for the pure tone; so a lower level of speech was required to reach LDL compared to the pure-tone stimuli.
August Roy Hernandez, M.A.-FAAA has been an Educational Specialist and trainer for Siemens Hearing Instruments for the past six years. Prior to Siemens, August worked in multiple private practice and hospital settings providing diagnostic services and audiologic rehabilitation for hearing impaired individuals.
For more information on Siemens, visit www.siemens-hearing.com