Banjos

Сентябрь 6, 2022

Содержание

2. BANJOS BANJOS ARE MAINLY OF THREE TYPES: 4-STRING BANJO WITH RESONATOR: POPULAR IN RAGTIME AND DIXIELAND
3. BANJO BANJO WITH RESONATOR OFF AND ATTACHED
4. BANJO SOUND A 5-STRING BANJO IS USUALLY TUNED TO D,B,G,D,G (294, 248, 196, 147, AND 393
5. BANJO SOUND FRACTION OF TOTAL SOUND UP TO AND INCLUDING HARMONICS Hn
6. MODES OF VIBRATION THE COMPLEX VIBRATION OF A SYSTEM CAN BE CONVENIENTLY DESCRIBED IN TERMS OF
7. HOLOGRAPHIC INTERFEROMETRY EXPERIMENTAL MODAL ANALYSIS MY BE ACCOMPLISHED USING ANY TRANSDUCER CAPABLE OF DETECTING MOTION, BUT
8. VIBRATIONAL MODES OF THE HEAD HOLOGRAPHIC INTERFEROGRAMS OF SEVERAL VIBRATIONAL MODES OF THE HEAD OF A
9. VIBRATIONAL MODES OF THE HEAD
10. HEAD MODES SPECTRUM FROM TAPPING HEAD SHOWING LOW-FREQUENCY HEAD MODES
11. RESONATOR THE RESONATOR VIBRATES VERY LITTLE. ITS MAIN ROLE IS TO DEFINE AN AIR CAVITY WHICH
12. EFFECT OF RESONATOR ON SOUND FRACTION OF TOTAL SOUND vs FREQUENCY WITH AND WITHOUT THE RESONATOR
13. BRIDGES BRIDGES ARE MADE OF DENSE HARDWOOD WITH A CAP OF EVEN DENSER WOOD. MOST BRIDGES
14. TRANSFER OF VIBRATION ENERGY WITHIN THE BANJO ACCELERATION AMPLITUDES OF VARIOUS PARTS OF THE BANJO WHEN
15. SOUND DECAY SOUND SPECTRA FROM 1st STRING EXCITED 1 INCH FROM THE BRIDGE RECORDED 0-2 s
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BANJOS
BANJOS ARE MAINLY OF THREE TYPES:
4-STRING BANJO WITH RESONATOR: POPULAR IN

RAGTIME AND DIXIELAND JAZZ; USUALLY PLAYED IN STRUMMING OR FLAT PICKING STYLE
5-STRING BANJO WITH RESONATOR: POPULAR IN BLUEGRASS MUSIC; USUALLY PLAYED WITH PICKS
5-STRING BANJO WITHOUT RESONATOR: USED IN OLD-TIME MUSIC; OFTEN PLAYED IN “CLAW HAMMER” STYLE (STRINGS ARE PICKED AND BRUSHED WITH THE FINGERS)
THE BRIDGE RESTS ON A MYLAR MEMBRANE WHOSE TENSION CAN BE ADJUSTED WITH A HOOP AND BOLTS
WITH THE RESONATOR IN PLACE, THE INSTRUMENT HAS AN ENCLOSED AIR CAVITY, AS FOUND IN GUITARS, VIOLINS, MANDOLINS, AND OTHER INSTRUMENTS. TUNING OF THE CAVITY IS POSSIBLE BY USE OF ADJUSTABLE SPACERS CALLED “RAEJUSTERS” WHICH CHANGE THE SPACING BETWEEN THE RESONATOR AND THE REST OF THE BANJO POT

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BANJO
BANJO WITH RESONATOR OFF AND ATTACHED

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BANJO SOUND
A 5-STRING BANJO IS USUALLY TUNED TO D,B,G,D,G (294, 248,

196, 147, AND 393 Hz, RESPECTIVELY). THE BRIGHT SOUND HAS MANY HARMONICS.

SPECTRUM OF BANJO SOUND FOLLOWING A PLUCK OF THE OPEN 1ST STRING

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BANJO SOUND
FRACTION OF TOTAL SOUND UP TO AND INCLUDING HARMONICS

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MODES OF VIBRATION
THE COMPLEX VIBRATION OF A SYSTEM CAN BE CONVENIENTLY

DESCRIBED IN TERMS OF NORMAL MODES OF VIBRATION. A NORMAL MODE IS CHARACTERISTIC OF THE VIBRATING OBJECT ITSELF AND IS NOT DEPENDENT ON HOW THE OBJECT IS EXCITED OR OBSERVED. FOR A MANDOLIN, A NORMAL MODE IS DETERMINED BY THE COUPLED MOTION OF ITS STRINGS, BRIDGE, HEAD, ENCLOSED AIR CAVITY, AND THE NECK/HEADSTOCK/FINGERBOARD ASSEMBLY.
THE DEFLECTION OF AN OBJECT AT A PARTICULAR FREQUENCY IS CALLED AN OPERATING DEFLECTION SHAPE (ODS). AN ODS MAY RESULT FROM THE EXCITATION OF MORE THAN ONE NORMAL MODE. A CURVE FITTING PROGRAM MAY BE USED TO DETERMINE THE INDIVIDUAL NORMAL MODES FROM THE ODS.

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HOLOGRAPHIC INTERFEROMETRY
EXPERIMENTAL MODAL ANALYSIS MY BE ACCOMPLISHED USING ANY TRANSDUCER CAPABLE

OF DETECTING MOTION, BUT HOLOGRAPHIC INTERFEROMETRY OFFERS THE BEST SPATIAL RESOLUTION.
ELECTRONIC TV HOLOGRAPHY IS A FAST AND CONVENIENT WAY TO RECORD ODSs FROM WHICH NORMAL MODES CAN BE DETERMINED.

SYSTEM USED FOR TV HOLOGRAPHY

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VIBRATIONAL MODES OF THE HEAD
HOLOGRAPHIC INTERFEROGRAMS OF SEVERAL VIBRATIONAL MODES OF

THE HEAD OF A HUBER LEXINGTON BANJO.

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VIBRATIONAL MODES OF THE HEAD

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HEAD MODES
SPECTRUM FROM TAPPING HEAD SHOWING LOW-FREQUENCY HEAD MODES

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RESONATOR
THE RESONATOR VIBRATES VERY LITTLE. ITS MAIN ROLE IS TO DEFINE

AN AIR CAVITY WHICH HAS QUITE A LARGE EFFECT ON THE HEAD VIBRATION AT LOW FREQUENCY. INCREASING THE SIZE OF THE RESONATOR-RIM GAP BY MEANS OF A RAEJUSTER INCREASES THE RESONANCE FREQUENCY OF THE ENCLOSED AIR CAVITY

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EFFECT OF RESONATOR ON SOUND
FRACTION OF TOTAL SOUND vs FREQUENCY

WITH AND WITHOUT THE RESONATOR

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BRIDGES
BRIDGES ARE MADE OF DENSE HARDWOOD WITH A CAP OF EVEN

DENSER WOOD. MOST BRIDGES HAVE 3 LEGS, ONE AT EACH END AND ONE AT THE CENTER. A USEFUL TRICK IS TO DRILL VERTICAL HOLES THROUGH THE OUTER LEGS WITH ALUMINUM RODS TO STIFFEN THE BRIDGE.

FRACTION OF SOUND vs FREQUENCY FOR TWO BRIDGES. BRIDGE 1 IS MADE OF A STIFFER WOOD THAN BRIDGE 2.

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