Roudolf Starobinski

The limit of absorbing characteristics of folded resonators silencers and ways of its realization

The folded resonance silencer is a version of 1/4‐wave resonator having a very compact shape. They are usually used for suppressing of narrow‐band and discrete frequency noise. The sets of resonators tuned to adjacent frequencies can be successfully used for a wide frequency band as well. The general theorems governing the behavior of these resonators are represented in this report. The limits of the muffling characteristics of the resonators and the ways of its realization are investigated on their base. It is shown that the potential muffling ability of a folded linear resonator is 1.2 dB less than for a Helmholtz resonator. However, taking into consideration the possibility of increasing the neck’s cross‐sectional area, they are more effective at high sound levels because of the higher quality factors. It is shown also that with the help of coupling folded resonators the resonance effects can be created in the frequency band wider than two octaves. These peculiarities make the use of the folded resonat...

The intake and exhaust noise control by influence on manifolds of vehicle engine

Excitation of eigenmodes in intake and exhaust manifolds of multi‐ cylinder internal combustion engine is investigated. It is shown that some of the eigenmodes do not depend very much on the intake, and exhaust systems are jointing behind the manifold. The sound increase (particularly for an asymmetrical excitation) caused by these modes depends on the degree of the asymmetry of the manifold and on sound energy dissipation in the manifold. Under some conditions this increase is the reason for resonance sound radiation. The tendency for resonance excitation at the branch of intake (exhaust) pipes with mufflers is considered to be one of the criteria in assessing the quality of manifold construction. Special attention is paid to the asymmetrical exhaust and intake manifolds of trucks. It is shown that the influence of the manifolds design of their engines allows a decrease truck intake and exhaust noise in a wide range of crankshaft RPM.