Abstract: An isosceles shaped sound reproduction speaker 70 is illustrated in the accompanying drawings and described in the specification. The speaker has isosceles sides that extend upward from an apex 86 at an internal angle of between 74.5.degree. and 79.degree. and preferably 78.4.degree.. The width of the enclosure is substantially equal to the circumference of the piston diameter of the primary dynamic, direct radiation diaphragm, low-to-mid frequency range driver 94 mounted in the front wall. The height "C" of the enclosure 71 is substantially equal to or less than the width "B" of the enclosure. The speaker 70 has a secondary dynamic diaphragm driver 98 mounted in the rear wall that is connected electrically in series with the front wall driver 94. The enclosure 71 has an upper fundamental resonance frequency of 2978 Hz.+-.3%. The front and rear drivers 94 and 98 have free air resonance frequencies that are 55 Hz.+-.3%.