Some Measurements on a Hyperbolic Horn Free

The coordinate system consisting of confocal ellipsoids and hyperboloids of one sheet yields a wave equation which may be separated. The resulting functions have been practically completely evaluated by Freehafer in some unpublished work at M.I.T. Rough experimental verification has been obtained for the amplitude and phase of the pressure field in a horn whose longitudinal section is a hyperbola with asymptotes 15° from the axis. A Hall type miniature condenser microphone was used; and the horn was terminated in the one bare wall of an otherwise well absorbing room. Because of the finiteness of the 6′ horn and incomplete absorption in the room at the lower frequencies, many irregularities are present in the field, but the essential features were found to have been correctly predicted. Transmission coefficient measurements are in progress, using electrical, acoustical and graphical means.