It is well known that plate radiation below the critical frequency is very poor, and therefore many stage floors dissipate low-frequency energy transmitted from double-bass and cello end pins rather than providing a tuning-fork/tabletop effect. However, if the stage floor is well damped, so that the transverse amplitudes fade out quickly around the point of excitation, a significant net radiation can be experienced also for low frequencies, due to the piston/baffle effect. Measurements performed in the Lindeman Hall of the Norwegian Academy of Music, in Oslo, Norway, showed that vibrational amplitudes in the stage floor faded out at a nearly equal pace in all directions around the excitation points, leaving nearly circular, quasi isotropic patterns for most frequencies of interest. In the audience area no tendency of spectral roll off was seen in the low-frequency end down to 30 Hz, which may represent the lowest fundamental of modern double basses. Transfer functions from stage floor to audience (intensity vs. power, and sound pressure vs. transverse velocity) were calculated for a number of seats in the hall.
QC 20140814