Hi all i am now prepar to write a essay about use sound to put off fire, and the pre-reserach i have done have show that the sound do can put off fire, however the very low efficient. What i want to find out how can i extend its distance to put out fire, i have try something ,and some of them works and some do not. i tried to use a tube which is filled with water, however it does not work at all, however when i used a hollow tube, and put it in the speaker, it do extend the distance. is there any other ideal to extend the distance????