The influence of the rise time on the loudness of sound pulses and the meaning of the sound spectrum on this influence were examined. A “paired comparison” method was used. The sound pulses had a duration of 0.7 to 1.0 sec and the rise time was varied between 0.03 and 1.0 sec. For most of the measurements, a signal level of 95 dBre2×10−5N/m2was used. The signals with the fastest onset showed the highest loudness. The influence of the rise time on the loudness was significantly dependent on the signal spectrum. The possibility of explaining the observed effects on the basis of changed synchronism of the neural activity and on the basis of a rapid adaptation in the nervous system is discussed.