Differences in nasalance scores obtained with different Nasometer headsets

The goal of the present research study was to investigate possible differences in nasalance scores between different Nasometer headgears. Frequency response characteristics of microphone pairs in a Nasometer model 6200, a model 6450 and two model 6500 headsets were compared using long-term average spectra of white noise and multi-speaker babble signals. Prerecorded sound files from a male and a female speaker were used to record nasalance scores with the four Nasometer headsets and to calculate cumulative absolute differences within and between the headsets. The main outcome measures were the cumulative absolute differences between the decibel (dB) values in the frequency bins from 300 to 750 Hz for the nasal and oral channels of each microphone pair. Cumulative absolute differences between nasalance scores of repeated stimuli within and across Nasometer headsets were tabulated. Results showed that cumulative absolute differences for the frequency range 300-750 Hz were between 6.58 and 7.68 dB. Within headsets, 95.6% to 100% of measurements of all four Nasometer headsets were within 3 nasalance points, although test-retest differences of up to 6 nasalance points were found. Between headsets, 56.1% to 98.9% of measurements were within 3 nasalance points, with the single largest difference of 8 nasalance points. In conclusion, differences between repeated nasalance scores obtained with the same and different headsets were noted. Clinicians should allow a margin of error of ±6 to 8 nasalance points when interpreting scores from different Nasometer headsets.