It has been shown in previous experimental studies on energy equivalent exposure to impulse noise that a shortening of the impulse duration and a corresponding increase in the number of impulses leads to a significant increase in the following variables: the temporary threshold shift TTS₂ immediately after the exposure, the restitution time to the complete abatement of the threshold shift t(0 dB), and the integral of the hearing threshold shifts (Integrated Restitution Temporary Threshold Shift or IRTTS). However, it has been unclear so far whether this increase in physiological cost is due to the shortened duration or the increased number of impulses. In order to study this question, 5 test series (TS I to TS V) were carried out with 10 (8 male and 2 female) test subjects from 22 to 41 years of age (27.1 ± 5.8 years) in each test series in order to analyze the effect of variations in the number of impulses with constant impulse duration as well as the effects of the impulse duration with constant number of impulses. The goal was to obtain information about the significance of the parameters “impulse number” and “impulse duration” with respect to the danger to the hearing from the stress of impulse noise by comparing the results of these tests. Consistent with earlier work, it was found that energy equivalent fractioning of continuous noise into impulse noise of shorter and shorter duration leads to an increase of the reversible effects of the noise exposure. If the differences (which are due to the test design) in the rating level (± 3 dB) are taken into account, the tests showed that an increase in the number of impulses leads to a high, i.e., over-energetic increase in the physiological cost (in the form of the IRTTS values) which is consistent with the pre-set hypothesis. With respect to impulse duration, there also exists a critical value; if the actual values are lower than this critical value, the effects of the noise exposure increase over-proportionally as well.