ES Surface 37 DB Range 930mm.Drop Down Seal. 930mm Surface 37db. A range of drop down seals for the bottom of doors also know as dropseals. The seals are activated by the closing action of the door dropping down to seal only when the door is closed. This leaves the threshold clear and flat without the need for high fixed thresholds. These seals have been tested without threshold plates and also straight down to carpet. They form an effective barrier against the outside climate,