Two cases of impulsive discharge, balloon burst and engine exhaust, are experimentally investigated to find scaling laws for the discharge time τ and the pressure amplitude A of the acoustic pulse. Observations show that the flow may be modeled as a pressure reservoir of dimension D and overpressure Δp suddenly discharging through an aperture growing with time. If W is a characteristic aperture velocity, the aperture area varies as (Wτ)2 for the balloon burst and as Wτ for the engine exhaust. The flow is driven by a complex, unsymmetric wave field within the volume. It is shown that D/τ∝ (CiW2)1/3 and A/Δp∝ (Ci/W)4/3 for the balloon burst, where Ci is the sound speed in the reservoir. The corresponding quantities for the engine exhaust pulses are (CiW)1/2 and Ci/W.