Abstract: Exhaust treatment devices and methods for reducing sound using the exhaust treatment devices are provided. In one exemplary embodiment, the exhaust treatment device includes a housing and a catalyst disposed in the housing. The exhaust treatment device further includes a first end cone having a first inner wall and a first outer wall. The first outer wall is secured to the first inner wall at one end. The first outer wall is secured to the housing at another end. The first inner wall is spaced from the first outer wall at the other end such that the first inner wall and the first outer wall define a first cavity therebetween. The first inner wall is spaced from the catalyst at the other end such that an inlet is defined that communicates with the first cavity, wherein exhaust gases flowing through the inlet into the first cavity attenuate sound within the first end cone and the housing.