Laser interferometry measurements of a Moroccan rabāb

Instrument: rabāb 
Country of origin: Morocco 
Place of origin: Fès 
Instrument maker: Abdessalam Chiki 
Year of manufacture: 2015 
Location: Basel, private property of Thilo Hirsch

Dimensions: 
Total length: 513.2 mm 
Max. Body width: 114.8 mm 
Width at the upper end of the skin: 96.2 mm 
Width at top nut: 31.6 mm 
Body depth at the upper end of the skin: approx. 80 mm

Vibrating string lengths: 
d-string: 410 mm 
G-string: 403 mm

Materials: 
Body: walnut 
Pegbox: walnut 
Fingerboard: Acajou (mahogany) 
Decoration: mother-of-pearl 
Bars: spruce 
Top nut, tailpiece button: Bone 
Bridge: bamboo 
Top: goatskin

Laser interferometry measurements: Alexander Mayer, mdw - University of Music and Performing Arts Vienna, Department of Music Acoustics – Wiener Klangstil (IWK), 18.2.2020

Each figure (Filenames: A_####Hz.jpg) corresponds to the frequency of excitation on the bass side of the bridge (shaker: Frederiksen Vibration Generator Nr 2185.00). Images are made by time-averaging of laser speckle interference at the camera (time-average ESPI approach). Operating deflection shapes (roughly translating to theoretical vibrating modes) are observed at each frequency.

Photo of the setup: Thilo Hirsch