Intended for teacher demonstration use the Rubens' Tube Pro is an exciting and very visual way to demonstrate the concept of a standing wave.By making measurements it is also possible to calculate the speed of sound. The Rubens' Tube Pro has a built-in amplifier so it can be driven by a wide range of signal sources including phones and tablets.Specification:Length: 2mSpeaker: 20W 8ΩAmplifier: 7W monoInput sensitivity: 40mVPower supply: 15V 0.5A dcGas supply: Natural gas or Propane (40 millibar max)