The object that produces the wave or disturbance.
A laboratory acoustic source is normally an acoustic monopole or at least behaves as one over a range of frequencies and is used for measurements of sound propagation, transfer functions or simply as a defined source.
This can be a voltage or current source and may be DC or a waveform generator.
Light emitting diode or Laser diode that emits light for launch into an optical fibre. Characterized by its central wavelength and spectral width.