A speaker has an annular magnet structure. First and second annular magnets are arranged concentrically with each other and connected by a shunt at one end and a pole-defining structure at the other end to concentrate magnetic flux in a cylindrical voice coil gap. The shunt and pole structure are stacked such that the combined magnetic assembly has an opening extending centrally therethrough. A voice coil rides in the cylindrical magnetic flux gap and its leads are brought out through the opening to the other side of the magnet. When used with an enclosure, the diaphragm of the speaker may communicate through the central opening with the volume of a tuned enclosure extending behind the speaker, or the opening may serve as a port of the enclosure, allowing further degrees of control over total acoustics.