BSA ABR Reference Levels for Stimulus Calibration
1 Reference levels in the table in bold are from ISO 389-6 (2007). Figures not in bold are where no values are available from ISO 389-6(2007) and are those recommended by BSA. Stimulus rate: 20/s. Adult listeners.
2 If the calibration is made using the same reference values with a 6cc coupler (IEC 606318-3) instead of an artificial ear, click and tone pip stimuli intensities are likely to be slightly greater at a given indicated hearing level. The differences are thought to be less than 2 dB. The 6cc coupler is therefore an acceptable alternative to the artificial ear, but if it is used the calibration would not comply with IEC 389-6.
3 Values for the Bayer DD45S supra-aural earphone are from PTB Physikalisch-Technische Bundesanstalt (2010). Chirp values from Interacoustics.
4 Warning: when using inserts, the sound pressure level in a neonate’s ear canal is likely to be 10-20 dB greater than it would be in an adult’s ear. This is an effect of canal volume. To avoid cochlear damage, never test babies at levels above 85 dBHL when using insert earphones.
5 A 2cc coupler (IEC 606318-5) is an acceptable alternative to an occluded ear simulator although its use does not comply with ISO 389-6. Reference values for the coupler can be derived from those for the ear simulator as follows: clicks: subtract 9.0 dB (Haughton, P. 2006. Int J Audial 45: 60-65); tone pips: subtract 4.0, 5.5, 8.5 and 9.5 dB at 0.5, 1, 2 & 4 kHz respectively (differences in the RETSPLs for continuous tones). The tabulated values have been derived in this way.
6 Reference values are for the B71 vibrator. Until a study provides values for the B81, use the B71 values; the manufacturer suggests this.
7 BC tone pip data have been derived by adding differences between the reference levels for tone pips and continuous tones (AC) to the ISO reference force levels (BC) for continuous tones. (Fedtke & Richter, 2007 and ISO 389-3). Interim values only.
8 The values for chirps and narrow band chirps were provided by Interacoustics.
9 The reference levels tabulated above are appropriate when using the peak-peak equivalent measurement method specified in IEC 60645-3 (2007). Equipment should be calibrated at a level that is comfortably above that of the background noise but low enough to avoid the risk of distortion. Recommended levels are 70-80 dBHL (AC) and 30-40 dBHL (BC).
10 “Clicks” and “tone pips / bursts” are the reference stimuli defined in IEC 60645-3 (2007).
11 These reference levels supersede previously recommended levels.
12 Please address any queries to admin@eratraining.co.uk
Changes from the previous version: (1) data for the DD45S earphone are now given. (2) B70 withdrawn and B81 now included.
~ The chirps referred to here are those specified by Elberling, C., and Don, M. 2008.
“Auditory brainstem responses to a chirp stimulus designed from derived-band latencies in normal-hearing subjects,” J. Acoust. Soc. Am. 124, 3022-3037
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