Is the equal energy rule applicable to impact noise?

The equal energy hypothesis (EEH) is a theoretical framework for evaluating the acoustic trauma associated with a wide variety of noise exposures. Most of the data supporting the EEH have been large scale demographic studies. Controlled laboratory studies, especially with impulse noise, have brought into question the generality and validity of the EEH. The present study assessed the hearing loss resulting from four impact noise exposures having equal energy, but different peak levels (107, 113, 119, 125 dB SPL) and repetition rates (4/s, 1/s, 1/4s, 1/16s). Hearing loss was assessed at 0.5, 2, and 8 kHz in four groups of chinchillas using the auditory evoked response. The animals were exposed for five days and developed an asymptotic threshold shift (ATS) during the exposure. The animals, however, did not develop the same amounts of ATS for each exposure as predicted by the EEH; instead the hearing loss increased with peak level.