Why Elbow Silencers?
The new generation of duct sound attentuators has brought about a markedly different silencer configuration than those seen in the past, the elbow silencer. Though met with much curiosity and skepticism, the elbow silencer is becoming more and more ubiquitous to the duct silencer and HVAC industries. Many designers are curious about the elbow silencer because it offers a new solution to an age old problem: lack of sufficient duct run to insert a traditional straight silencer. Many designers are also skeptical of the elbow silencer because it seems to go against standard low static pressure design methods as well as requiring an extra amount of effort to specify and schedule. Sizing an Elbow Silencer Traditionally, silencers have three dimensions that need to be specified: width, height, and length. For a straight silencer, it is fairly self-explanatory to which areas these dimensions refer. In the case of an elbow silencer, this can be more difficult to ascertain. Elbows can be oriented two possible ways in a duct system, with the elbow turning parallel to the ground or perpendicular to the ground. In both elbow configurations, the three primary dimensions still refer to the same orientation with the width dimension always horizontal. Another element of confusion with regard to sizing the silencer is whether to use the centerline length or the leg lengths (denoted by L1 and L2). ArtUSA uses both of these dimensions in our  submittals, though for different purposes. The centerline length is used for acoustical performance and pricing.  The leg lengths are used in the submittal stage in order to give the engineer or contractor exact external dimensions of the silencer. This helps to insure the designer that the silencer will fit in the relegated space within the duct system. Though the engineer usually specifies the centerline length in the schedule, once the leg lengths have been determined by ArtUSA, the centerline length can always be calculated. To find the center-line length: add up the two legs and then subtract one duct width from that sum. When sizing an elbow silencer, one should always keep in mind the limitations of the elbow silencer design. In order to manufacture a silencer that can perform at the required levels, the inside legs (see image) of the silencer have a minimum length of 12" each. This is due to the silencing pods within the silencer. The pods cannot make a turn of greater than that radius and still be aerodynamically and acoustically effective. In the reverse case, there are no maximum sizes on elbow silencers. Just as with rectangular silencers, the elbows can be made into banks of silencers to accommodate silencers larger than the maximum module size.