Duct mounted sound attenuating baffle with an internally suspended mass layer
A sound attenuating baffle mounts within the duct section of an air distribution HVAC system, a ventilation system, or other air movement system for either air or gas streams, in which the duct section can be mounted directly to a fan or incorporated into a transmission duct. The sound attenuating baffle is typically oriented in the flow direction through the duct, and includes an outer casing containing sound absorbing material therein. An internal mass layer formed of a sound barrier material is suspended within the sound absorbing material which fills the outer casing. The mass layer increases the low frequency sound attenuation of the sound attenuating baffle.
1. A sound attenuating baffle device for use in a duct receiving a gaseous flow in a flow direction therethrough, the baffle device comprising:
an outer casing including two opposed faces having i) a length spanning in a longitudinal direction between a leading end and a trailing end of the outer casing, ii) a width spanning in a lateral direction between opposing sides of the outer casing, and iii) a thickness between the two opposed faces which is reduced in dimension relative to the length and the width, the outer casing being adapted to be supported within the duct such that the longitudinal direction is aligned with the flow direction;
a fibrous sound absorbing material occupying a hollow interior of the outer casing between the two opposed faces, the sound absorbing material being arranged to absorb sound by dissipation of sound energy as sound travels through the sound absorbing material; and
a mass layer comprising a sheet of metallic material which is dense in relation to the fibrous sound absorbing material;
the mass layer being suspended within the hollow interior of the outer casing so as to span a majority of the width of the outer casing and a majority of the length of the outer casing in spaced apart relationship to both of the opposed faces of the outer casing;
a perimeter edge of the mass layer being suspended to be spaced apart from a material of the outer casing about a full perimeter of the mass layer by the sound absorbing material which fully surrounds the mass layer; and
the mass layer being fully suspended relative to the outer casing by the fibrous sound absorbing material which is under compression between the mass layer and the outer casing.
2. The device according to claim 1 wherein the mass layer comprises a uniform, non-porous sheet.
3. The device according to claim 1 wherein the mass layer is supported equidistant to the two opposed faces across the length and the width of the outer casing.
4. The device according to claim 1 wherein the mass layer comprises a sheet of metal.
5. The device according to claim 1 wherein each of the two opposed faces of the outer casing comprises a perforated sheet material.
6. The device according to claim 1 wherein the outer casing is adapted to span a full width of the duct in the lateral direction.
7. The device according to claim 1 in combination with at least one auxiliary baffle identical in configuration to the sound attenuating baffle device in parallel and spaced apart relation to the sound attenuating baffle device.