jwilzewske: Messing About in Harpsichords: DIY Ceramic Plectra

T he sound of the harpsichord resembles that of a bird-cage played with toasting-forks... No, it is more like two skeletons copulating on a corrugated tin roof.”
— Sir Thomas Beecham, British conductor (1879-1961).

S omtimes I cannot leave well-enough alone. An amateur guitarist friend at work was showing me his nice, new pick—made of some exotic ceramic material. The manufacturer of the pick is very mysterious and non-forthcoming with regard to what the “specially-formulated”, lubricious, hard material is. But junior Archimedes that I am, I go and measure it—measure its density, etc.—and I suspect (but do not know for certain) that it is boron nitride.

I think: “That is really cool! But why should guitarists have all the nice toys? What about harpsichordists?”

T here are all sorts of other technical materials that are used for musical instruments that are specially selected or constructed so as to achieve physical properties that vary by desirable amounts, in desirable directions.

T hink graphite violin bows: how far they have come in the past 20 years. Think Michel Wegen graphite-epoxy composite guitar picks. Think ceramic composites in jet engine turbines. Think exotic dental composites and orthopedic surgery ceramic composites. Think yttria-stabilized zirconia cutlery in your kitchen!

I n one of my former lives, I did some semiconductor engineering and physical electronics. I have a slab of silicon nitride lying around. I look up the Young’s modulus (elastic modulus) and other physical properties of the silicon nitride and compare it to the properties of Delrin™ and of bird quill. Hmmm. I go down to my basement shop at home and begin slicing up my little left-over silicon nitride slab into plectra-shaped bits.

T he machining of the plectra is pretty straightforward, if you are a rockhound and have some lapidary and faceting tools and some diamond bits for your Dremel MotoTool™ (or comparable 20,000 rpm flexible-shaft hand tool). I used 400-grit diamond for most of the cutting, and 14,000-grit and 30,000-grit cerium oxide powder for the polishing work.

T he ceramic surfaces are polished to nanometer smoothness so that they will not abrade the harpsichord strings.

H ere is a drawing of my ceramic plectra:

McNair silicon nitride harpsichord plectra

T hey are quieter and slipperier than Delrin™ plectra. The sound of the harpsichord tongues and jacks would not be at all affected by these exotic ceramics. The “ceramic vs. Delrin™ vs. quill” noise differences I’m talking about are only about the noise of the plectrum tip itself, just as it slips against the deflecting string before the plectrum excursion (or string deflection) is large enough that the plectrum releases the string.

I think the only person who can possibly hear the “scritch” of Delrin™ acetal plastic against the strings is the performer a few inches away. With nitride, there is no plectrum-against-string noise at all.

T o everybody else, the pleasant harpsichord “action-falling” sounds with ceramic plectra like these should be identical to the ordinary mechanism quilled with conventional plectrum materials.

R emains to be seen, but I suspect these technical ceramics may give much lower “wear” compared to Delrin™ or quill? Much less frequent need for re-voicing and re-quilling? Other advantages?

I do suspect that plectra made out of such ceramics will, in general, give a “brighter” sound—maybe brighter than purists would find desirable, who knows? But the toughness of these materials might open up new horizons of harpsichord dynamics and expression.

A nd I have no doubt that the “springiness” (nitride elastic modulus ~ 200 GPa, compared to Delrin™ and bird quill elastic modulus ~ 3 GPa) will give a ‘faster’ action than Delrin™ or quill.

H ere is a little Excel spreadsheet I put together, modeling the stiffness of Delrin™ plectra of different dimensions. (I have a similar spreadsheet for my silicon nitride plectra.)

Spreadsheet model of Delrin™ plectra stiffness

W hat else? The nitride materials do not undergo ‘work-hardening’. They do not get brittle like Delrin does with elapsing time and more playing. And the nitride composites have very low coefficients of friction (somewhat lower than zirconia, as I recall). Other advantages, too.

A nyway, the possibility of helping to advance the state of harpsichord technology intrigues me. Why is the ‘business end’ of the harpsichord sound-producing mechanism still stuck with Delrin™, same as Hubbard and others used 50+ years ago!

A lso, you may want to give a look at Lorna Gibson’s new materials science book, on composites (link below). More ideas for innovative plectra materials! No reason why homogeneous, nearly-isotropic (same properties in all directions, along all axes) like Delrin or ceramics is the only way to go.

jwilzewske

Thursday, June 17, 2010

Messing About in Harpsichords: DIY Ceramic Plectra

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