JFA (J URNAL FISIKA DAN APLIKASINYA) VOLUME 17, NUMBER 1, JANUARY 2021 Evaluation and Analysis of Uncertainty Measurement of The Sound Level Meter Calibration by Coupler Method Bondan Dwisetyo and Denny Hermawanto Badan Standardisasi Nasional, Kompleks PUSPIPTEK Gedung 420, Serpong, Tangerang Selatan 15314 Abstract: The calibration of sound level meter (SLM) using a coupler method has been introduced. This method utilizes a multifunction acoustic calibrator as a portable laboratory instrument. By the reason of its convenient application, it is appropriate to be realized by the secondary calibration laboratory. To complete the requirement of calibration result provided by ISO 17025, an analysis of the uncertainty measurement related to this calibration is strongly needed. Therefore, this work aims to provide an evaluation and analysis of some ele- ments that influence to the coupler method of SLM calibration using the statistical approximation to determine the major parameters such as standard uncertainty, combine uncertainty, degree of freedom, and expanded un- certainty in accordance with The Guide to the expressions of Uncertainty in Measurement (GUM). Moreover, a case study related to this instrument calibration also discussed along this paper. From the result, the uncertainty budgets that contribute to the SLM calibration has been obtained, and generally, it is found that the standard instrument has the highest contribution to the determination of the expanded uncertainty. For the whole results, the obtained uncertainty values are still acceptable according to the acceptance limit values that required by IEC 61672-1. Keywords: calibration of sound level meter; coupler method; GUM; uncertainty measurement. *Corresponding author: bondan@bsn.go.id Article history: Received 2 May 2020, Accepted 25 August 2020, Published January 2021. http://dx.doi.org/10.12962/j24604682.v17i1.6988 2460-4682 c Departemen Fisika, FSAD-ITS I. INTRODUCTION The calibration of the acoustical instruments such as a mi- crophone, a sound calibrator, and a sound level meter, has be- come the trending topic in a Metrology area in recent years [1]. The sound level meter, known as SLM, is considered as the most applicated device by the users among these in- struments, and the customer needs related to this instrument calibration tend to increase [2]. To accommodate their neces- sity, the calibration of SLM has been provided by the National Standardization Agency of Indonesia (BSN) as the represen- tative of the National Metrology Institute (NMI) of Indonesia by using the absolute method. To realize this method, it is necessary to utilize a full anechoic chamber as a calibration medium, and the laboratory standard of a microphone as a reference device [3]. Even though this method is capable to assure the calibration result so accurately, this method is diffi- cult to be applied because of its complexity to be implemented and have a very high financial budget, especially for the sec- ondary calibration laboratory. Furthermore, the other method has been introduced, where it is known as the coupler method that uses a multifunction acoustic calibrator as the portable laboratory instrument, and utilize a small insulation box as a calibration medium [4]. This method is quite simpler than the previous method, and it is ap- propriate to be applied by the private calibration laboratories to comply with the industrial necessity for the SLM calibra- tion that tends to increase by a year. However, this method is considered as the new method in Indonesia relatively, where the calibration result is necessary to be discussed comprehen- sively. According to the requirement of calibration and test- ing provided by ISO 17025, the uncertainty measurement as a main part of the calibration result needs strongly to be evalu- ated and analyzed [5]. Therefore, the objective of this work is to provide an eval- uation of the uncertainty measurement of SLM calibration by the coupler method using the statistical approximation to de- termine the major parameters such as standard uncertainty, combine uncertainty, degree of freedom, and expanded un- certainty in accordance with The Guide to the expressions of Uncertainty in Measurement (GUM). Moreover, a case study related to this instrument calibration is also discussed along with this paper, where the result will be compared with the acceptance limit value required by IEC 61672-1. In addition, the calibration and measurement capability (CMC) of sound level meter calibration using this method also is planned to be proposed to the Committee of National Accreditation (KAN) as the representative organization for local accreditation. II. MATHEMATICAL MODEL The calibration of sound level meter by coupler method is conducted using the multifunction acoustic calibrator as the laboratory precision instrument, and diagram of the calibra- tion system is shown in Fig. 1. Additionally, to optimize the calibration process, it is nec- essary to make use of an insulation box as the calibration