Caracterização dinâmica de um instrumento musical de cordas usando análise modal operacional

Abstract

Although the electric guitar has been more and more an investigation object by the academy, there are still important conclusions missing regarding its dynamic characteristics. To offer a contribution over this panorama, a modal analysis was performed having a beam and a Squier by Fender Stratocaster 50 th Anniversary guitar as objects. Altogether with experimental bench tests, analytical and modeling strategies were employed to the AISI 1020 steel beam, while the musical instrument had its dynamics described only with the aid of empirical inputs. For the tests, impacts of unknown force were deployed on two locations of both objects, that were instrumented with four ADXL 335 accelerometers each and connected to a National Instruments cDAQ-9178 chassis equipped with a NI-9201 voltage modulus for the data acquisition. An Arduino UNO board was used as voltage source for the sensors. After data processing via MATLAB, the natural frequencies of 7.34, 65.43 and 107.35 Hz, respectively for the 1 st , 3 rd and 4 th vibrational modes of the beam and 56.08, 140.65, 185.50 and 210.90 Hz for the guitar’s 1 st , 2 nd , 3 rd and 4 th modes were obtained. An Output-only modal analysis (OOMA) Frequency Domain Decomposition (FDD) algorithm was performed for the beam and the guitar, resulting in correct shapes for the 1 st , 3 rd and 4 th beam modes and the 1 st , 2 nd and 3 rd guitar modes. It was verified that poor sensor positioning and implementation of the experiment hindered some of the result reached. In general, it was concluded that the FDD technique must be aligned to other excitation methods in order to fully work, while natural frequencies can be accessed through simpler methods.