Well-designed silencers to deal with low frequency noise

The company attributes this to its ability to attenuate the exhaust noise of an engine at critical low frequencies. Noise from the auxiliary engines of a large carrier vessel was measured at such a high level that the ship, heading out from the Middle East, was not granted permission to enter a major European natural gas terminal. Because it is obviously not possible to use an alternative port, the only alternative was to find a way of reducing the noise levels from the five 3,500kW engines.

More detailed investigation showed that the cause of the excessive noise levels was that the silencers fitted were unable to attenuate low frequency exhaust noise efficiently. According to Silentor, no silencer is better than its ability to reduce the A-weighted noise at the dominant frequencies. Attenuation of non-dominant frequencies alone does not achieve satisfactory overall atenuation.

Silentor’s solution was to design superior-performance silencers for the ship. These silencers had to meet strict constraints, such as they could not be larger than the existing silencers, and should not create a larger pressure drop. Also, to install the silencers, it was necessary to divide each into several parts, and re-assemble them when they were correctly located within the ship. Despite these challenges, the five silencers were designed, constructed and successfully installed. Subsequent sound tests showed significantly different attenuation at the low frequency range. Which the company attributes to the creation of very narrow passages between the chambers, resulting in a superior sound attenuation in the low frequency range.

The company says that poor attenuation at low frequencies is not a new problem, but all-too-often low-frequency noise is accepted causing great inconvenience to the crew aboard ships; it is also a great nuisance when vessels are near residential areas. There is no reason to tolerate this noise, because proper;y-designed silencers are able to attenuate the exhaust noise at the critical frequencies.

The results with the new silencers led to a further 18 ships being fitted with Silentor silencers, after which the vessels had no problems entering the terminal.