Hearing Protection (Ear Defenders): Rigid Cups on Liquid-Filled Cushions (Shaw & Thiessen, NRC, US 2,801,423, 1957)

Ear muffs that seal well and still stop low-pitched noise. Each ear is covered by a rigid cup on a cushion made of a thin PVC tube, emptied of air and part-filled with liquid. Pressed on, the liquid flows round the whole rim and fits the cushion to the head, yet cannot compress, so the cup does not vibrate as a whole and pass the sound in. A sprung headband with a pad holds the cups on ball joints. Result: circumaural ear defenders effective against low-frequency noise. Source: E. A. G. Shaw and G. J. Thiessen (National Research Council of Canada), US 2,801,423 (1957). Unknown: sizes and the attenuation achieved. Picture: the patent drawing.

متوسط

Unknown

التعليمات

Make the cups

Make two rigid, non-porous cups to go over the ears, of wood, a hard plastic or a light metal such as aluminium. Widen each rim to about the width of the cushion, and make a small hole in the rim for the cushion's filling nipple. Fix a ball joint on the back of each cup. Not given: sizes.

المواد لهذه الخطوة:

مادة غير معروفة2 أكواب

معدن غير معروف2 ball joints

الأدوات المطلوبة:

مخرطة معادن

أبعاد غير معروفة

Make the liquid cushions

For each cup make an endless tube of thin, pliable but non-stretching plasticised PVC, 0.005 to 0.01 in thick, with a filling nipple. Draw out almost all the air, then fill it with liquid to more than a quarter but well under the whole of its cross-section: enough to reach right round the rim when pressed, not so much that it cannot seal. Fix it on the rim with the nipple in the hole. Ours: water as the liquid. Not given: tube size.

المواد لهذه الخطوة:

لوح PVC1 thin plasticised PVC tube

ماء1 filling

الأدوات المطلوبة:

طقم محاقن

Fit the headband and wear them

Make a resilient headband frame with a sponge-rubber pad at its middle and a wire loop at each end. Through each loop pass a threaded stub from the cup's ball joint, with a washer, and tighten with a wing nut. Put the cups over the ears: the cushions take the shape of the head and seal, while the cups stay still against the low-frequency sound. Ours: spring steel for the frame.

المواد لهذه الخطوة: