Tom, yes I've thought about aspect that since I posted originally. I'm still amazed that screws alone could have a big impact on sound in a typical speaker mounting situation. The low mechanical impedance of brass is still constrained by the gasket material around a speaker basket, the vibratory characteristics of the speaker basket, and the vibration damping capacities in the many materials used in a speaker. I wonder how much relevance can be drawn from the musical instrument analogy. An instrument is designed to vibrate and radiate sound, no surprise increasing mechanical coupling to the floor enhances sound. A speaker, to greater or lesser degree depending on manufacturing budget and skill of designer, is supposed to be as inert as possible. Of course we know from looking at all of the accelerometer graphs in Stereophile that all cabinets vibrate to greater or lesser degree, so the coupling angle you mention may well be a factor. This all got me wondering what effect might be had from using brass or bronze as speaker basket material instead of the usual suspects.