Abstract: A method of recording sound for reproduction by a plurality of loudspeakers, or for processing sound for reproduction by a plurality of loudspeakers, is described in which some of the reproduced sound appears to a listener to emmanate from a virtual source which is spaced from the loudspeakers. A filter means (H) is used either in creating the recording, or in processing the recorded signals for supply to loudspeakers, the filter means (H) being created in a filter design step in which: a) a technique is employed to minimise error between the signals (w) reproduced at the intended position of a listener on playing the recording through the loudspeakers, and desired signals (d) at the intended position, wherein: b) said desired signals (d) to be produced at the listener are defined by signals (or an estimate of the signals) that would be produced at the ears of (or in the region of) the listener in said intended position by an source at the desired position of the virtual source.

Abstract: An article having a spallation resistant TBC comprises a metal substrate, such as a high temperature superalloy, and a TBC, such as a coating of yttria stabilized zirconia. The TBC comprises a plurality of plasma-sprayed layers. The TBC has a coherent, continuous columnar grain microstructure, wherein at least one layer has a plurality of continuous columnar grains which have been extended by directional solidification into an adjacent layer. In a preferred embodiment, the coherent, continuous columnar microstructure comprises substantially all of the volume of TBC. A coherent, continuous columnar grain microstructure is also taught wherein at least some of the plurality of coherent, continuous columnar grains which comprise a TBC extend through essentially the entire thickness of the coating.

Abstract: Embodiments of a pipeline repair habitat are disclosed which may be used to facilitate the repair of vertical underwater pipelines or risers. Two hollow, half-cylindrical shells are provided which form a stable, rigid shell around the section of pipe to be repaired. Structure is provided for introducing an atmosphere into the habitat which is breathable while most repairs are accomplished. Under certain conditions a non explosive atmosphere which is not breathable is introduced into the habitat so that welding may be safely performed. Various useful accessories are provided including an elevator by which a person accomplishing repairs may move up and down within the pipeline repair habitat.

Abstract: A stereophonic sound reproduction system is aimed at synthesizing at a multiplicity of points (L) in the listening space. An auditory effect obtaining at corresponding points (K) in the recording space, to compensate for crosstalk (C.sub.21, C.sub.12) between the loudspeakers, the acoustic response of the listening space, and imperfections in the frequency response of the speaker channels. Each speaker channel incorporates a digital filter (H) with the characteristics of which are adjusted in response to measurements of the reproduced field. The digital filters are provided by an inverse filter matrix (H) of which the matrix elements (H.sub.ij) are determined by a least squares technique, applied so as to minimize the sum of the squared errors resulting from the difference between the actual system impulse response and a desired impulse response. A full bandwidth signal is transmitted by a bypass route for combination with the output signal (9) from the filter, the bypass route including a delay means (F).