Selection of mounted tuning forks and rubber hammer.

How it works:

Each tuning fork is mounted on a wooden sound box to amplify the sound (they're very difficult to hear without the box). A microphone/preamp/scope setup may be used to visually demonstrate the pure sinusoidal sound wave. Additionally, a frequency analyzer shows a single frequency component (however, if the gain is turned up high, you may also see the frequency components due to the resonances of the sound box or harmonics of the tuning fork if it was whacked too hard). One of the 256 Hz tuning forks is also adjustable in frequency so that beats may by heard when it is sounded simultaneously with a regular 256 Hz fork. Alternatively, beats may be produced by walking briskly away from the class towards the blackboard with tuning fork in hand. The simultaneous receding and approaching (via a blackboard reflection) tones of the tuning fork interfere and produce beats (from the students' frame of reference). The following table lists the various frequencies that we have available with comments.

* These notes are based on the Scientific or Diatonic Scale in which C₃=256, thus making computations simple. The Equal Tempered Chromatic Scale has A₃=440 which makes C₃=261.63 The notes of the scale are variously designated in different countries. Being made in France, these tuning forks have the French inscriptions; the first six notes bear the names given by the monk Guy of Aresso in 1026. They are the beginnings of words which occur in a hymn to Saint John the Baptist, and are as follows: ut, re, mi, fa, sol, la. The seventh syllable, si, was added in 1684 by Lemaire. In Italy do was substituted in place of ut, because it was easier to pronounce in singing. In England the notes were named after the first letters of the alphabet. In Germany, H is substituted for B.

Comments:

The tuning fork was invented by John Shore, a trumpeter in the service of George I of England, in 1711, nearly three hundred years ago. The resonant case was added subsequently by a French instrument-maker, Marloye. A good tuning fork will "ring" for a couple of minutes. This requires a special metal alloy (ordinary steel won't work, for example). Modern tuning forks are typically some hard aluminum alloy. Most of ours are not aluminum and were made in the 1850's by Dr. Rudolph Koenig (they're inscribed with his initials) and sold by Marloye & Co. in Paris (owned by Koenig's father-in-law). Needless to say, these tuning forks are priceless antiques and should be treated as such. It appears that they were quite valued even when new as is evidenced by this quote from Sound and Music, by J.A. Zahm (McClurg & Co., Chicago, 1892): "The making of a perfect instrument—especially if that instrument be a tuning fork or a wave siren—is for Dr. Koenig a labor of love. It is for this reason that the tuning forks which bear his stamp are so universally sought, and, when secured, are so highly prized."

You will notice that the frequencies have the units of vs (vibrations/sec) and the number indicates the number of vibrations from the equilibrium point rather than our present day reckoning of frequency, which is cycles/second (cps). Thus, the inscribed number is actually twice the frequency of the tuning fork.