<p style="text-align: justify;">Acoustic resonance is a physical phenomenon in which in-phase sound waves combine together to produce maximum amplitude; on the other hand, out-of-phase sound waves cancel each other to produce minimum amplitude. The purpose of this study is to investigate and demonstrate this phenomenon with the use of a reliable device. This study requires a modified resonator tube apparatus to be developed and fabricated from locally-available materials for the purpose of demonstrating resonance and normal modes of sound waves. Air column length versus harmonic number (L vs n) and frequency versus harmonic number (f vs n) experiments were performed together with open-pipe and stopped-pipe procedures. For L vs n experiments, deduced value of speed of sound is 337.79±0.94 m/s at 760 Hz for open-pipe taken at 29°C; and 357.72±9.34 m/s at 412 Hz for stopped-pipe taken at 25°C. For f vs n experiments, deduced value of speed of sound is 337.09±5.98 m/s at 2.30 m for open-pipe taken at 25°C; and 345.92±5.55 m/s at 1.60 m for stopped-pipe taken at 30°C. Results had shown that the modified resonator tube apparatus is accurate and precise within 5% margin of error. Therefore, the apparatus is a reliable device in demonstrating acoustic resonance phenomenon in the physics classroom setting.</p>