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Listening Equipment "Waalsdorp"

  The initial plaster and paper execution of the paraboloids was replaced by a vertically balanced metal version. This was joined to a vertical column to which was mounted a seat for the listening operator. The adjustment of the chart angle in the horizontal plane around the column took place by muscle force of arms and legs. Great care was devoted to the smooth and noiseless operation of this vertical bearing without play or backlash. The best listener thus achieved an accuracy of less than one degree in chart angle using the time difference in arrival between the two signals.

Similar care was spent on the construction of the two horizontal bearings for the elevation adjustment through the centres of which the sound received, was transported to the ears. An inflatable ring shaped rubber cushion filled the space between each bearing and the ears of the listener. Helped by flat partition walls in each paraboloid the operator could reach an accuracy of less than two degrees in elevation using sound intensity only.

According to this model 18 equipments were built by industry from 1934 for the Engineers Regiment and the Netherlands Army in the East Indies. A report, dated 10 April 1934, mentions a series of thirty additionally delivered listening equipments and a new series of 80 in production.

Listening equipment 'Waalsdorp'front
Listening equipment "Waalsdorp",
front side and listening operator
(full size 222 KB)

Listening equipment

Listening equipment "Waalsdorp",
back side with the scale reading
operator for the chart angle and
(full size 200 KB)


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