Abstract: A method of flow modulation was developed for large power pneumatic loudspeaker to reduce gas consumption and background noise.A modulation method of the flow control is provided to perform advanced sound performance and high effectiveness with large gas-sound ratio.First,a full modulation is studied in a model to find its principle of sound generation by gas from horn throat.According to this model,modulator of pneumatic loudspeaker is adjusted in none-flow when in static state,sound wave is pre-processed to cut its lower envelope to form a new signal to control the gas-flow.This flow is proportional to sound's amplitude.The sound's property is much better than before with less gas wasting.Four different typical modulation models are discussed in comparing their effectiveness.For a typical male's speech signal,comparing with half-flow modulation,gas utilization ratio of this full modulation is enhanced from 5% to 51.5%,for a sinusoidal wave sound,the ratio keep in a maximum 60%in different modulation-rate,SNR of the sound generating is enhanced over 15 dB.