The loudness of transient sounds has been studied as a function of four physical parameters: intensity, rise time, duration and frequency. This has been done by presenting pairs of gun shots or pulses from a transient sound generator to subjects. The transient sound generator was constructed especially for this experiment and it allowed absolute control of the physical parameters. The subjects estimated the ratio of the loudness of the sounds in each pair (i.e., ratio estimation). Four experiments have been carried out and in each of these, one of the parameters has been varied, while the other three have been kept constant. For intensity, rise time and duration a linear relationship with loudness on a log vs. log plot was found. The correlation was strong, implying that the relationship is a power function. The slopes of these three different curves agreed with those obtained in previous experiments, while the results from the experiment with varying frequency clearly differed from those expected. The greatest inconsistency was that the I kHz and the 4 kHz pulses were regarded as equally loud, while the loudness level curves of Fletcher and Munson show a difference of 13 phons.