The AAF Tubular Duct Mute is available in 3 standard designs. 

TDM, for standard applications, is available in two standard length-to-diameter ratios and two pressure drop categories. TDM-P, for pressure applications less than 10 PSIG, is available in two standard length-to-diameter ratios and two pressure drop categories. TDM-8L, for lines 8" and less, is available in six standard line sizes with specific lengths.