Spessori di tavola e fondo – appendice

Come produrre, ascoltare e rilevare le note (frequenze dei modi) dei piani armonici.
How to produce, listen and detect the notes (mode frequencies) of the plates.
Index of videos :
ENGLISH TRANSLATION of the written notes in the video, in order of appearance :

00:05 – Top and Back thicknesses – How to produce, listen and detect the notes of the plates

00:18 – Top and the back plates free from the ribs produce some notes to the percussion that correspond to characteristic modes of vibration, called starting from the lowest in frequency M 1, M 2, M 3 and so on as the frequency increases. To excite one mode, hold the plate with two fingers along a nodal line (non-motion zone) by tapping the fingertip of the other hand in an antinodal area (motion zone) while listening to the note produced.

00:41 – With a trained ear the detection of notes can easily be done based on listening and comparison with reference notes, or you can use electronic systems such as tuners or computers by placing the microphone in place of the ear at the listening points. This allows a better perception of the minimum frequency variations and to know the numerical values

01:17 – The most useful modes for the luthier are M 1, M 2 and M 5 also called cross mode, “X” mode and ring mode with reference to the geometry of their nodal lines. They correspond to the torsional, lateral and longitudinal flexures that are carried out with the hands during working to test the flexibility of the plates. Mode 5 is the most effective indicator of the stiffness in relation to the mass and can be taken as a useful reference during the thicknessing of the plates

02:52 – Detection systems
The analog chromatic tuner (Korg AT12) will provide only the note and the pitch shift in hundredths of a semitone. In addition to the previous data, the digital tuner (App G String, on the telephone) can also provide the frequency in Hertz. The spectrum analyzer (Audacity free software) is very effective as it will allow you to read very clearly the peak frequency of the various modes.

04:06 – How to do and what to hear
Hold the plate between the thumb and middle fingers of the left hand with the least possible pressure at one of the nodal points (P) indicated in the image. Tap with the tip of the ring finger (not the fingernail) of the right hand at an antinodal point (A) indicated in the image and listen or place the microphone at the same point on the opposite side of the plate. If necessary, slightly move the fingers that grip the plate until you find the best point to hear a clear and resonant note

04:10 – Mode 5 Back – P = Grip points – A = Listening points

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