A new audio transducer for mobile devices having a collar with side openings that provide side venting to a back volume within an enclosure. The side openings eliminate the need for a typical frame and back vents thereon, which leads to a smaller size speaker. Each of the side openings have a maximum size less than the size of an adsorber material, which prevents the adsorber material coming into contact with the magnets, coil, and membrane of the speaker. The side openings and the size thereof also permit the enclosure to be directly filled with an adsorber material. The direct filling of the adsorber leads to more even and complete distribution of the adsorber within the back volume, which, in turn, improves sound quality of the speaker.