The Sonometer is an acoustic demonstration instrument comprising a wooden resonance box with two one-meter rules for precise measurement. It is used for studying the relationships between string tension, length, density, and the frequency of vibration, making it a fundamental tool for physics instruction in wave mechanics and sound. The resonance box measures 114 cm in length, 12.5 cm in width, and 10 cm in height, providing ample amplification for the vibrating wires. The instrument comes with one brass wire and one steel wire of different diameters, each attached to a fixed bridge and tensioned by fine adjustment pegs. Two moveable bridges allow the effective vibrating length of the wire to be varied precisely, while a pulley and fixed screw enable a third wire to be attached for tensioning by hanging masses. The two rules are subdivided into millimeters for accurate length measurement. One additional wire each of steel and brass, each 1.5 m long and of 22 SWG, are included as spares or for comparative experiments.