Several automobile companies are also experimenting with active mufflers as a way to control engine noise with less back pressure than a conventional muffler. The main benefit is more peak horsepower from the engine. Active silencers for large fan systems - low frequency noise from fans can be attenuated with active cancellation systems. The primary advantage is reduced flow resistance compared with standard duct silencer technology. The active silencers utilize passive elements such as duct lining to control high frequency noise.
Several manufacturers offer active silencers for industrial and fan systems.
A length of straight duct between the fan and the silencer is required, making active silencers impractical for most remedial noise problems in air conditioning systems. The future will bring systems that can control higher frequencies and larger sound fields, but with current technology, once the noise enters a room it is too late to apply Active Noise Control. For further information on Active Noise Control, visit the ANC faq home page Sound Isolation - Doors Doors are often the weak link in sound isolation between spaces. Doors without sound gaskets provide only 20 dB of sound isolation. Addition of sound gaskets at the perimeter and threshold can improve this to the 30 dB range for a solid core door.