Odstraňování vlivu velmi hlubokých a širokých nepůvodních vpichů/vrypů na jádřekovové varhanní píšťaly barokního typu na zvuk píšťaly
The elimination of impact of the deep wide unoriginal nicks/notches in the languid of the baroque type metal organ pipe on pipe sound
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1. Introduction For centuries, nicks in the languid of the labial metal could be found in organ pipes throughout the world. It is one of the techniques of pipe voicing adjustment (an overview of voicing techniques see e.g. in: [www1]; [Otčenášek Z., Dlask P., Syrový V., Hruška V., Otčenášek J., 2018]). The use of nicks differs between countries, districts, organ builder schools, and also between different cultural times. In Czech historical lands, the principal pipes in baroque period were built mostly without nicking (together with the used of low air pressures in windchest). If nicks were used than they were typically slim, low deep, and sparse (from 3 to 7 at languid width). Later, in romantic time, when some baroque organs were romanticized, nicks were doubled (up to tripled) and enlarged (being deeper, broader and wedged). Nowadays, Czech historical organs can be found with original baroque pipes without any modification (original state), with the addition of unoriginal romantic nicking later added to original pipes as well as pipes presenting both types of nicks concurrently. Less often we can find an organ with the pipes where the large number of deep broad notches were made at the edge of the languid resembling the teeth on a saw. In such cases the material of the languid was partly excised, and partly pressed and displaced below both the bottom edge and over the side walls of the saw teeth. In the last decades, when historical organs have had to be restored to original stage, also restoration of original sound was required; the elimination of the unoriginal nicks influence on the sound is necessary. Since the saw notches introduce heavy damage to the languid material, their elimination is an ongoing problem yet to be solved. Nowadays, the restoration of such organ with the saw notches can be 1) kept the pipes unchanged (what gives unsatisfactory, not eliminated influence on sound) or 2) cleared away with the common technology of smoothing (proper for thin nicks (Otčenášek Z., Koukal P., Švejda M. Moravec O., Dlask P., 2014); at saw notches, however not possible to get back the excised material and to correctly move back the displaced material; consequently the languid edge stay with the ripples). The present study verified a third possibility in which a new method of replacing the damaged languid by new ones is done. Since the cutting of the languid and soldering of a replica is considered an invasive intervention, the method was experimentally verified on the copies of historical pipes with identical modifications made (the original pipe being untouched). A replica model of the historical principal metal pipe (SupOctava 2, tone d1 [Dlask P., Otčenášek Z., Kopeček Š., Vorlíček M., Koukal P., Otčenášek J., Frič M., Hruška V., 2018]) from the Jesuit church in Klatovy (Czech Republic) was used (original can be seen in top of figure Obr. 1, replicas underneath). All copies were voiced at optimal sound for the air pressure in windchest of 55 mm H2O (539 Pa). The copies had very similar sound (see spectra in figures Obr. 4). Similar results were obtained also after each modification of the pipes; therefore, only results from measurement of only one replica pipe are presented here. 2. Method Acoustical measurements were performed in anechoic room (see figure Obr. 2). The recordings (wav format) were made with 24 bit A/D conversion, sampling frequency 48 kHz. The signal of tone attack was synchronized with the opening voltage of electromagnet of air valve (0 s). The FFT of spectrograms (see figures from Obr. 13 to Obr. 16) were computed with 42,66 ms hanning time window and 2,13 ms shift. The spectra (see figures Obr. 4, Obr. 11 and Obr. 12) are the average of 60x FFT with hanning time windows 682,66 ms and 13,66 ms shift. 3. Experiment The sound recordings, the spectra analysis, and listening tests with recorded sounds were done after each step of pipe modifications. 3.1. The documentation of default manufactured pipes without nicks was the first initial step (see figures Obr. 1, Obr. 3, spectra are in Obr. 4, and spectrogram of pipe K3 in Obr. 13). The frequency of 1st harmonic fo, pipe body length, cut-up height, cut-up with, slit breadth, foot length, foot opening diameter of measured pipes are in Tab. 1 (from left to right). The pipe K4 was used as a reference (without other alterations; the K4 spectra measured in the time after each step of other pipes show the temperature and humidity influence on results and repeatability of the method used, see figure Obr. 11). 3.2. In the second step the deep breadth saw notches were created (see figure Obr. 5). The notches where not accurately the same at all pipes (figure Obr. 6) but in spectra of all pipes we observed great lowering of both high harmonics (see difference between the red and green curves in figures Obr. 12) and noises (see sound pressure levels in figure Obr. 14). 3.3. In the third step the saw notches were cleared away by the common technology of smoothing. The material overhanging the languid edge from the bottom was pushed up from bellow by the metallic rod (see figure Obr. 7 left) through pipe foot. The saw teeth were aligned by other metallic tool by pushing both the material displaced from bottom and the tips of the saw tops back inside the teeth (see figure Obr. 7 right). After this step none of the pipe languid edges was straight (see languids after smoothing in figure Obr. 8 top; and languid detail viewed from the bottom after smoothed languids were cut out in next step see in figure Obr. 8 bottom). 3.4. The last step was the replacement of the languid by a new one. The authors were not experienced with this procedure. Firstly, all labial diameters were documented. Then a cut was made with a thin saw (cut width cca 0,2 mm) at the foot close to the languid (cca 0,5 mm) (see figure Obr. 9 left). The next cut was made in the upper edging of the languid (see languid in figure Obr. 10 top). Then the potential defects at foot, labium and pipe body were cleared and an accurate copy of languid was made (without nicks and notches). The languid replica was soldered at the foot and body (see figure Obr. 10 bottom). The cutting-up process of replacing the languid slightly changes the length of pipe and fo frequency (new values see in Tab. 2 in comparison with Tab. 1). 4. Acoustical results and assessment The results of the acoustical analysis demonstrate that the creation of deep breadth saw notches at pipe languid produced major changes in the pipe’s sound and tone attack. Changes were observed in the spectra of the established tone, the sound pressure waveforms and spectrograms of the starting part of the tone (figures Obr. 12 and Obr. 14). If the lowering of higher harmonics (green in figure Obr. 12) is not compensated by increasing the air pressure in the windchest (it was compensated in the case of organ romanticized modifications), a degradation of the organ sound can be noticed. The common smoothing method gives increasing of harmonic amplitudes at maximum 1/3 of their original values and therefore is not proper for the elimination of saw notches influence on pipe sound. When the sound of a historical organ needs to be restored, the windchest air pressure will be decreased when compared to the original baroque value and therefore it must be accompanied by the removal of the unoriginal saw notches. The results verify that, if the languid replica and soldering is done properly, and the languid cutting-up is replaced with a copy without notches, the original sound can be replicated. The sound before and after the substitution of the languid is not distinguishable when listen, and the spectra and spectrograms are similar (compare red and black curves in figures Obr. 12 or figures Obr. 13 and Obr. 16). 5. Conclusion The authors are aware that the experiments were performed on new pipes in which the material was not corroded, and without damage what occasionally occur in historical organs. Therefore, the new languid cutting-up and replacing method of saw notches elimination can not be directly used on historical pipes. Additional experiments have to be carrying out in order to ascertain such possibility.
- www1: http://www.orgel−info.de/aktuell.htm, 23 X 2018. JANKE, R. (2015): Parameter die den Klang einer Labialpfeife beeinflussen.
- Otčenášek Z., Dlask P., Syrový V., Hruška V., Otčenášek J. (2018): Retná varhanní píšťala a její základní intonační nastavení, Praha: AMU.
- Otčenášek Z., Koukal P., Švejda M. Moravec O., Dlask P. (2014): Změna zvuku kovové píšťaly barokního typu technologií vpichů na jádře, Praha: MARC AMU, Technologický list TL66/14.
- Dlask P., Otčenášek Z., Kopeček Š., Vorlíček M., Koukal P., Otčenášek J., Frič M., Hruška V. (2018): Odstraňování vlivu velmi hlubokých a širokých nepůvodních vrypů na jádře kovové varhanní píšťaly barokního typu na zvuk píšťaly, Praha: MARC AMU, Technologický list TL89/18.
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