Rene Morel Metal Ruler Lesson

[dpappas]

In previous threads, an anecdote emerged about Rene Morel thumping a ruler that was hanging off the table, and retracting it as it oscillated.  It was related to sound post fit and tone.

I've been thinking about this (and whacking metal rules for a good twenty minutes), and I'm asking the experts if my understanding is correct.  A tighter post would allow less vibration, but would also favor higher frequencies.  A looser post would allow more plate movement, but at the same time would favor higher frequencies.

I know this is an oversimplification, but I found that shaving a think slice off a sound post and putting it in the same position resulted in a similar effect, a deeper tone.

[Don Noon]

28 minutes ago, dpappas said:

I'm asking the experts if my understanding is correct.  A tighter post would allow less vibration, but would also favor higher frequencies.  A looser post would allow more plate movement, but at the same time would favor higher frequencies.

A cantilevered beam (ruler) and a tighter post have nothing in common that I can see.  However, there might be some analogy concerning the distance between the soundpost and the bridge foot, where more distance = stronger driving of the lower frequencies (or mid-frequencies, since the bass foot is doing the low-frequency stuff).

[Bill Yacey]

A sound post applies a preload force between the plates. The more preload, the more stifled movement will be between the plates. The reason high frequency is favored when a post is fit tight is because the plate as a whole doesn't need to move to reproduce the high frequencies.

Removing the low frequencies from the spectrum simply leaves the high frequency content.

It is this idea of preloading that I reject the need to pre-stress = (preload) the top plate when installing it. Tension resists movement.