The posaune is a reed stop with wooden pipes, certain pipes are detuned in order to create a vibrato effect.
THe Principal or Diapason is the most common organ stop, being the classic organ sound. There are few organs that are without a diapason. It is an open flu with pipes of metal and little 'wings' or 'ears' protruding ftom the side of the fipple.
The diapason, in its 16' or 32' pitches often forms the façade of the organ, being easily recongnisable as an 'organ pipe'
The principal is often played with multiple octaves above and below, with 'mutations' or stops pitched at consonant intervals above or below the note being played. It is often coupled with a 'mixture' or a set of mutations at 1' or ½' pitch to make the recognisable 'Great Organ' sound
Above is a principal with an octave above (4') to simulate a great organ-ish sound.