First Acoustic Images of a Master-Class Violin
The 16 channels data stream is characterized by smooth, flat waves, 50.000 Samples per second. The period is 384.6 Hz. Click the image to hear the sound! Some times one can see the third harmonic in form of waves with double peaks. The following picture shows the arrangement of the array: the numbers mark microphone channels of the array. The violin is played in a distance of 50 cm to the array in the position drawn.
Reconstructive acoustic interference integral over an interval of 164 ms. The image is overlayed by a hand sketch. Click the image to find an image with a higher resolution and dB-scale with maximum value algorithm.
Find a sequence of 25 images refering to 385 Hz in the next video. The source of the movie (AVI) is here (ZIP), 10.000 images per sec. integrated over 1ms each, 170k/620k.
The next video shows a high-speed movie too with 25000 images per second. It shows a sequence of 66 images refering to 385 Hz. Here is the zipped source (zipped AVI), 25000 images per sec. integrated over 1ms each, 295k/1.6M.
Relative to channel sound pressure (52.9 dB) the effective value of the interference images (see behind above image) lays between 34.6 and 44.8 dB. It means, that each place in the interference image is at maximum -10 dB or factor 1/3 so loud as the channels effective value is.
In opposite to cars or motorbikes, fine, smooth and closed waves in the interference images and movies are typically for the violine. The oscillation of each part can be observed in the movies. The body seems to oscillate around a center point. Sometimes it is possible to see a weak emission where the stroke of the bow meets the violin. The left hand attenuates the vibration and emmission, so it is marked mostly by a blue region. The end of the grip emmittes more.
Please take notice, that the player was not in an optimal recording position. Some microphones get direct waves from the front side and the bottom side of the violin. Because it is to suppose, that each side of the violin oscillates different to others, we were surprized to get sound locations at all.
- At that time we did not know anything about artefacts, like room-resonances, diffraction effects and phase shifts at the violins body at that time.
- The 16-channel array, the recorder and PC we used is shown here.
The world of violins:
Geigenbaumeister Joerg Mayer
D-09427 Ehrenfriedersdorf, Germany
for the possibility to take the records and to
Dr. sc. Friedrich Blutner
Am Waldsportplatz 1
D-09468 Geyer, Germany
for his invitation.
Ips: Images per second
Sps: Samples per second
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file created Febr. 20, 1998
AVI to MP4 konvertiert, Layout angepaßt, 7. Febr. 2023