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Transmission loss (TL) in duct acoustics describes the acoustic performances of a muffler-like system.It is frequently used in the industry areas such as muffler manufacturers and NVH (noise, vibration and harshness) department of automobile manufacturers, and in academic studies.
A sound attenuator, or duct silencer, sound trap, or muffler, is a noise control acoustical treatment of Heating Ventilating and Air-Conditioning (HVAC) ductwork designed to reduce transmission of noise through the ductwork, either from equipment into occupied spaces in a building, or between occupied spaces.
For all new or replacement train horns on trains capable of travelling up to 100 mph (160 km/h) a much lower minimum sound pressure level has been established – and a maximum sound level has been introduced (min 101 dB and max 106 dB). British train horns have two tones, high or low, and in some cases, a loud or soft setting.
Silencer (silver) and exhaust pipe on a Ducati motorcycle A silencer cut open to show the insulation, chambers and piping inside the shell. A muffler (North American and Australian English) [1] or silencer (British English) is a device for reducing the noise emitted by the exhaust of an internal combustion engine—especially a noise-deadening device forming part of the exhaust system of an ...
Another common type of muffler is the chambered muffler, which consists of a series of concentric or eccentric pipes inside the expansion chamber cavity. These pipes allow sound to travel into them and cause the sound waves to bounce off the closed, flat ends of the pipe. These reflections partially cancel each other out, reducing the sound level.
The glasspack is an old, simple, and relatively inexpensive muffler design that has less back pressure than other types of muffler, but is less effective at muffling noise. A longer glasspack will reduce noise to a greater extent than a shorter one, as sound is dissipated into the fiberglass damping material.
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B-weighted sound pressure level is written either as dB B or L B, and C-weighted sound pressure level is written either as dB C or L C. Unweighted sound pressure level is called "linear sound pressure level" and is often written as dB L or just L. Some sound measuring instruments use the letter "Z" as an indication of linear SPL. [13]