A perforated plate flow conditioner includes a single acoustic feedback interference device having an upstream end attached to a downstream side of the perforated plate. The upstream end covers substantially all of the downstream side of the perforated plate between two adjacent holes. The volume of a downstream end of the interference device is less than the volume of the upstream end. In another embodiment of the invention, the upstream end of a single acoustic feedback interference device covers substantially all of the spaces between a central hole and all of the surrounding adjacent holes. In another embodiment of the invention, all of the spaces between adjacent holes are substantially covered by upstream ends of acoustic feedback interference devices.