The double bass and cello sections in the orchestra transmit vibrations to the stage floor through the end pins. Whether or not these vibrations may contribute to the perceived sound in the hall has been investigated since the 1930s. In this study the conditions for an efficient transfer of instrument vibrations to the floor, as well as the radiation from the floor to the audience area, are investigated. The study includes measurements of the impedance matching between bass and stage floor, the vibration velocity transfer to the floor via the endpin, and radiation from point-driven bending waves in the stage floor well below the coincidence frequency. The impedance conditions and radiation properties of the stage floors of five concert halls were investigated. In the two most promising halls, full-scale experiments were run with an artificially excited double bass supported via the end pin on the stage floor and on a concrete support below, respectively. The contribution from the stage floor radiation to the sound level in the audience area was 5 dB or more between 30 and 60 Hz. This range covers the fundamental frequencies over one octave starting from the lowest note (B0) of a five-string bass.