No John, No! The airbrakes on a glider control RATE OF DESCENT. THEY DO NOT CONTROL THE AIRSPEED.
The speed is controlled by the attitude of the glider. Nose down, goes faster. Nose up goes slower.
The effect of the airbrakes, which on most gliders look like slices of toast sticking out of a toaster, when fully deployed will dramatically increase the rate of descent....in short, you are no longer flying a craft with a 27 to one glide ratio, but one more like a Cessna with a 10 to one glide ratio. Delightfully confirmed by the demonstration of trying to land with no airbrakes deployed at all, on a best glide speed of say 50 knots, and the glider will carry on floating into the next county!