The pipe organ offers the opportunity to conduct psychoacoustic experiments in which the sound of a natural instrument can be perfectly steady and reproducible. This study takes advantage of the pipe organ to concentrate on that aspect of musical dynamics determined by the physical parameters of steady sounds, leaving aside the admittedly important effects of other variables such as context and articulation. Juries of musicians and music students provided judgments of musical dynamic levels produced by steady sounding of various stops and combinations on two pipe organs. The physical strength of each of these sounds was measured, and they were analyzed in octave band spectra. Correlations between the physical parameters and the musical judgments were examined. Results of this study provide some support for the hypothesis that loudness calculated by a procedure such as Zwicker's will be a good predictor of the steady aspect of musical dynamic strength, whereas a simple unweighted sound level in decibels is rather poor.