The Sound Characteristics Of The Baglama With Respect To Differ- ent Chest Shapes Sinem Öztürk 1 İstanbul Technical University İTÜ Gümüşsuyu Kampüsü, Makina Fakültesi, 34437, Beyoğlu - İstanbul / Türkiye Filiz Yücel Gürer 2 Ankara Music and Fine Arts University Turan Güneş Bulvarı Yukarı Dikmen Mahallesi, Neşet Ertaş Caddesi, No:4 06550 Oran Çankaya/An- kara/TÜRKİYE Özay Önal 3 Ankara Music and Fine Arts University Turan Güneş Bulvarı Yukarı Dikmen Mahallesi, Neşet Ertaş Caddesi, No:4 06550 Oran Çankaya/An- kara/TÜRKİYE

ABSTRACT Baglama is the most common folk string instrument in Turkey. It has a bowl-shaped resonator box called a chest which amplifies the sound. The chest can be constructed in various forms by the luthiers. This study aims to determine the sound characteristics of the baglama associated with dif- ferent chest forms. First, a prototypical baglama was modeled and analyzed numerically with the SolidWorks, HyperMesh and Actran software programs. Operational Deflection Shape (ODS) meas- urements of the baglama were also carried out experimentally. The numerical results were compared with the experimental ones and had an excellent agreement. Using this experimentally validated nu- merical model, the natural frequencies, mode shapes and sound propagation properties of the bag- lama were investigated for chests of different geometries.

1. INTRODUCTION

Although there are few publications in the literature on Bağlama acoustics, studies in the national field have gained momentum in the last 20 years. As the baglama is an instrument whose material is wood, it undergoes some deformations over time. One of them is the soundboard collapse. Similar problems exist in instruments such as guitar, oud and violin. The problem was tried to be solved by adding balcony laths to the inside of the soundboard. A similar method has also been tried in baglama to prevent the soundboard from collapsing (Aktaş, 1999; Coşgun, 1991; Demir, 1996). It has been stated that gluing the balcony laths made in different lengths, thicknesses, and heights to different parts of the soundboard positively affects the sound. However, this described effect was not measured

1 ozturksi@itu.edu.tr

2 filizyucel@mgu.edu.tr

3 ozayonal@mgu.edu.tr

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by any tool and was limited to personal evaluations. It is also unknown whether the soundboard col- lapses over time and thus whether the experiments have worked.

The vibrations that occur in the strings of the bağlama are transferred to the soundboard. In oud and guitar, the strings are connected to a piece on the soundboard. However, in the baglama, the strings are connected to the wire plug at the end of the boat. In this part, the wire plug and the lower threshold are together. As a result, different forces and pressures act on the soundboard of the oud and guitar, unlike the baglama. Demir studied a baguette produced according to this setup and com- pared the resulting sounds with another traditional baglama (Demir, 2002). At the end of these com- parisons, based on personal perception, without using any measurement tool, it was stated that the vibration duration of the sounds increased, the loss in high-pitched sounds decreased and the harmon- ics became more pronounced.

In another study, a two-piece soundboard is used instead of a one-piece soundboard, balcony laths are added to the simple soundboard, new sound holes are drilled on the soundboard instead of the soundhole at the bottom of the wire insert, and a mechanical auger structure is preferred instead of a wooden auger. Baglama and a cura were produced (Erdis, 2006). This baguette and cura produced were compared with two baglamas and two cura in the classical structure. The sounds obtained from these instruments were compared to sound intensity and resonance times. It was determined that the sound intensity of the new baguette increased, but the expected increase in the resonance times could not be observed.

Çiçekçioğlu (2017) made a baglama according to the golden ratio in his study and compared it with another traditional baguette. The sounds obtained from both baglamas were recorded with a sound recording program on the computer and the sound intensity-time graphics were examined. In his study, Akaltan (2017) modeled the body and cover of the guitar using ANSYS software and de- termined the resonance mode shapes of the body and cover with the help of this model. In the guitar, the force applied to the cover and the resulting deformation resulting from connecting the strings to the body at different angles were examined with the help of SOLIDWORKS software. It was deter- mined that the angle with the least buckling effect of the strings was 60°. Resonance mode shapes were determined by modeling the boat and soundboard of the baglama using similar methods. Ac- cording to the results obtained, guitar and baglama were compared.

In another study, Alp (2018) investigated the effects of the change in the boat size of the baglama. In this context, it has been ensured that only the hull sizes of the two baglamas produced from the same material with the same thickness and method are different. This study determined that the bag- lama sound board's size changes affect the baglama's acoustics.

In this study, a bağlama with a widely preferred body form was constructed using wooden material whose parameters were already decided. After performing required experimental studies on it, the 3D solid model of the baglama was generated. After validation studies of the numerical model, the mode shapes of the baglama were determined by making a modal analysis. Then, keeping all the parameters constant in the baglama model, it was examined how the acoustic properties of baglama changed due to the changes to be made only on the body form. Natural frequencies and mode shapes were exam- ined for those different body forms.

2. NUMERICAL MODEL

The solid model of the baglama, which was manufactured during the preparation phase, was cre- ated by taking the draft drawings and curves with the reverse engineering method and "3D surface scanning" process.

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This geometry obtained is the geometry that references numerical studies that experimental studies have verified. This created model was also arranged with the help of the SOLIDWORKS program and grouped into three parts called the handle, the cover and the tub. The solid model of the manu- factured coupling (reference coupling) is shown in Figure 1 below.

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SOUND BOARD

Figure 1: Solid model of the fabricated baglama.

The finite element models of the experimentally examined reference coupling and couplings with different hull geometries were created with the HYPERMESH program. The dimensions and types of the finite elements were determined under the frequency range of the analysis. The handle and cover parts of the designed baglama models are the same as the reference baglama. The design was carried out only for the hull part.

There are finite element models created with the HYPERMESH program belonging to both the reference body and other bodies designed in different geometries, with the neck and soundboard common to all models.

Figure 2: Finite element models of the neck and soundboard of the baglama.

Finite element models created with the HYPERMESH program of bodies designed in different geometries are given in Figure X.

Figure 3: Finite element models of the baglama bodies designed in different geometries.

3. EXPERIMENTAL MODEL

The experimental data of the study were obtained by the method called "Operating Deflection Shapes" (ODS). The photographs of the apparatus used in the experimental study are shown in the figure below.

Figure 4: The apparatus used in the experimental study.

The transducer is placed on the lower threshold of the neck and is connected to the amplifier. When the soundboard is vibrated, black powder is sprinkled on it better to observe the vibrating and non-vibrating parts of the soundboard. Dust particles began to spatter once the soundboard resonated in response to the appropriate single frequency sound from the transducer.

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4. RESULTS AND DISCUSSION

With the modal analysis applied to the reference baglama, the model was transferred to the MSC. ACTRAN program, the natural frequencies of the structure and their corresponding mode shapes were determined. Under experimental conditions, modeling was carried out to verify the natural fre- quency and mode shapes obtained from the experimental studies performed on the same coupling.

The natural frequencies corresponding to the modes detected in 0 – 1000 Hz in the experimental study with the reference coupling.

The natural frequencies obtained from the experimental and numerical analysis with reference coupling and the % difference between them are given in the table below.

Table 1: Natural frequencies obtained from experimental and numerical analysis and the difference

between them.

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The mode shapes corresponding to the natural frequencies determined in the experimental study with the reference baglama are shown in the figure below.

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Figure 5: Mode shapes obtained from experimental studies with reference baglama.

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Figure 6: Mode shapes obtained from numerical studies with reference baglama.

The following figures show the natural frequencies and mode shapes obtained for the reference baglama and the baglama with two different hull geometries.

Figure 7: The natural frequencies and mode shapes obtained for the reference baglama.

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Figure 8: The natural frequencies and mode shapes obtained for the first designed baglama.

Figure 9: The natural frequencies and mode shapes obtained for the second designed baglama.

5. CONCLUSIONS

In this study, experimental ODS analyzes were performed on a reference baglama. The numeri- cally generated finite element model was validated using these experimental data. Two different mod- els were designed by changing the geometry of the soundboard of the validated baglama model. As a result of the study, natural frequencies and mode shapes were obtained for the new baglamas de- signed.

This study is the first study in which such detailed acoustic analysis has been made in baglama acoustics. In future studies, it is planned to focus on more detailed and more sensitive experimental and numerical studies and to carry out more comprehensive studies. 6. REFERENCES

1. Aktaş, B. Changes in the Soundboard with the Balcony Application in Baglamas (Org.: Bağla-

malarda Balkon Uygulamasıyla Ses Tablasında Meydana Gelen Değişiklikler.) Master Thesis, Istanbul Technical University, Social Sciences Institute, İstanbul, 1999.

2. Demir, O. New Practice on Threshold System in Baglama. (Org.: Bağlamadaki Eşik Sistemi

Üzerinde Yeni Uygulama.) Master Thesis, Istanbul Technical University, Social Sciences Insti- tute, İstanbul, 2002. 3. Erdiş, E. New Approaches to Acoustic Analysis and Development of Baglama. (Org.:Bağlamanın

Akustik Açıdan İncelenmesi ve Geliştirilmesine İlişkin Yeni Yaklaşımlar.) Master Thesis, Cum- huriyet University, Social Sciences Institute, Sivas, 2006. 4. Çiçekçioğlu, Ü. Innovative Approaches in Baglama Production. (Org.: Bağlama Yapımında Ye-

nilikçi Yaklaşımlar.) Master Thesis, Ege University, Social Sciences Institute, İzmir, 2017. 5. Akaltan, A. Acoustic Analysis and Inspection of the Baglama Body. (Org.: Bağlama Gövdesinin

Akustik Analizi ve İncelenmesi.) Master Thesis, Bahçeşehir University, Institute of Science, İs- tanbul, 2017. 6. Alp, M. Effect of Wooden Boat Size on Acoustics in Baglama Instrument. (Org.: Bağlama

Enstrümanında Ağaç Tekne Büyüklüğünün Akustiğe Etkisi.) Master Thesis, Hacettepe University, Institute of Science, Ankara, 2018.

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