Ensuring The Eclipse Is Working Properly; Calibration Of Eclipse - Interacoustics Eclipse Additional Information

Eclipse Additional Information Page 5

2 Ensuring the Eclipse is working properly

2.1

Calibration of Eclipse

It is recommended that an Interacoustics distributor calibrate the instrument once a year.
Two types of calibration are used in the world of AEP – peSPL (peak equivalent Sound Pressure Level) and
nHL (normal Hearing Level).
peSPL is an objective measure of the sound stimulus pressure level. For a given peSPL dB value, the max
acoustical or vibration level is calibrated to match the level of continuous tones used to obtain the same
dBSPL reading on a sound level meter. As the duration of sound stimuli for AEP are extremely short, the en-
ergy delivered is not perceived with the same subjective loudness as the equivalent stimulus would provide,
if it were a continuous tone. Therefore the acoustical or vibration value given in dB peSPL does not corre-
spond very well with normal HL figures. For Clicks there is a 35.5dB difference (70dBpeSPL sounds as
35dBHL), and for Tone Bursts the differences are in the 20-30dB range depending on frequency and number
of sine waves used in burst.
Stimulus intensity is limited to 135.5dBpeSPL by the transducers.
nHL is a correction, which compensates for the difference in perceived loudness of the very brief stimuli like
Clicks and tone bursts. There is therefore a direct similarity between the indicated level in nHL and the HL
levels well known from normal audiometry. Brief tone burst correction values from peSPL to nHL are based
on a 2-1-2 manual burst as specified in ISO 389-6-2007. Longer duration tone bursts for AMLR and ALR are
employing peRETSPL values similar to continuous pure tones (as used in conventional audiometers) since
the temporal integration of tones lasting at least 50ms is considered sufficiently trivial to ignore.
Note Reference calibration values for the CE-Chirp® stimulus family are not specified in the current interna-
tional calibration standard (ISO 389-6), and the applied peRETSPL values have therefore been derived from
two studies: (1) by PTB in Germany (2008), and (2) by DTU in Denmark (Gøtsche-Rasmussen et al., 2012).
The mean of the values obtained in the two studies, rounded to the nearest 0.5 dB, are used by Interacous-
tics A/S to calibrate the broad-band CE Chirp® LS and the four frequency specific NB CE-Chirp® LSs deliv-
ered by the ER-3A earphone.
The following tables give the reference equivalent thresholds for various stimuli in dB peSPL and dB peVFL
Note The RETSPL figures given for ABR 3A inserts are for measurements made in an occluded ear simula-
tor (IEC 60318-4 / 60711) not a 2cc / HA-2 coupler, for which different values apply. Unofficial figures for the
HA-2 coupler are available at: http://hearing.screening.nhs.uk/calibration.
Remember to check Eclipse stimuli levels. An easy sound check with the transducer left on the table
is often a good manual weekly procedure.