2.1.1. Noise

A handmade soundproof box was used in the noise experiment as shown in Figure 2, and the rotary fan adopted in the subsequent experiments was used in the sound proof test. The material of the soundproof box sheet is acrylic having a thickness is 5 mm and the size is 350 × 250 × 250 mm3, which is covered with wave-shaped soundproof cotton with a thickness of 50 mm. The decibel meter named by DSL-333 (Tecpel Co., Ltd., Taipei, Taiwan) as a measurement range between 30 and 130 dB with a resolution of 0.1 dB and an error of ±1.5 dB and the frequency response is between 30 Hz and 8 kHz. Outside the box, the rotary fan produced a noise with a value of 62.4 dB, while when placed inside the soundproof box, it produced a noise measured at 50.7 dB. The background

volume of the testing room was measured to be 41.6 dB, yet after correction according to the standard noise control Equation (1), that value was corrected to 50.1 dB. This proves that the soundproof box has good soundproofing ability. The volume correction of the background was displayed in Equation (1).

$$L\_0 = 10\log\left(10^{0.1L\_1} - 10^{0.1L\_2}\right) \tag{1}$$

*L*0: Measured value of the intended sound source


**Figure 2.** Noise experiment.
