Abstract: Sound absorber comprising a large number of tubular resonators (10) whose sound orifices A.sub.o are adjacent to a common surface A and are distributed in such a way that the interaction zones A.sub.w of these individual sound orifices A.sub.o are distributed as far as possible over the whole surface and at the same time do not substantially overlap. Preferred embodiments consist of extruded plastic shaped parts (16) or of metallic shaped parts (7, 9) which are firmly connected to one another and have suitable mechanical rigidity and acoustic hardness.

Abstract: A balancer mass is reciprocated linearly in the plane of the piston/cylinders of a four cylinder in-line engine by a pair of cams mounted on the crankshaft for rotation therewith. The second order vibrations can be substantially eliminated either by mounting a single balancer of the invention at the center of the crankshaft or by using a pair of balancers mounted one each at opposite ends of the crankshaft. The vibrations can also be substantially reduced by mounting a single balancer at the "free end" of the crankshaft opposite the clutch and flywheel.