Objective quality is a general term used to denote those physical characteristics thought to govern the subjective quality of an instrument, and depends ultimately on the instrument geometry and material composition. Other physical characteristics (such as acoustic impedance) may be capable of being related both to subjective and objective quality and this paper examines the extent to which acoustic impedance may be used as a predictor of subjective quality. Based on previous work, three simple hypotheses are put forward and examined by subjective experimentation. It is shown after experiments on large bore tenor, bass, medium bore tenor trombones and a straight tube that no hypothesis as it stands may be used as a guide to subjective quality, but that a procedure based on assessing the envelope of the impedance curve of the instrument may be of value. Observations on various parameters such as internal cleanliness and mouthpiece bore are mentioned in view of the lack of published evidence on these features.