The material of a sonometer wire is not fixed and can vary depending on the experiment or application. However, the wire is typically made of a strong, elastic material that can vibrate at a controlled frequency. Some common materials used for sonometer wires include:

* Steel: A popular choice due to its strength, elasticity, and relatively low cost.

* Brass: Offers a slightly different tone and can be more resistant to corrosion than steel.

* Copper: Provides a softer tone compared to steel or brass.

* Nickel: Offers a bright and clear sound, but it is more expensive than steel or brass.

* Piano wire: A high-quality steel wire designed for use in pianos, known for its consistency and ability to produce clear notes.

The choice of material will influence the wire's tension, diameter, and density, all of which affect the frequency at which the wire vibrates.