Hi. As part of our physics course we have to make an independant investigation into a subject of our choice. I took a simple sound absorption idea. Basically, i took a signal generator, a speaker, and a decibel meter. With the speaker and the decibel meter 30 cm apart and a material in the middle to measure the relative sound level detected. That was the first experiment i did. In an ajoining small room, in an english science lab. so all the walls and floors are hardwood or brick. The readings seem kinda erratic, as the different readings are all out of phase. I really don't know what to pin the readings down to, so i don't know what i'm measuring here. I thought that the peaks and troughs on the graph could be attributed to minimums and maximums of the waveform. But then after a long, painful, amount of time i think i was just getting mixed up and of standing waves (where the minimums and maximums would remain stationary and not move throught the air?) I'm supposed to be analysing that data but I really dont know what im' doing and i'm getting kinda desperate. ------------- after taking those readings i hadnt graphed them because they looked too random. (stupid mistake) so i moved into a different room (bigger room with less clutter) and took another set of readings. this time, i was fortunate to have a laptop with me so i took waaay more readings as most of it was automated. I get something completely different, the amplitude drops dramatically below 250 hz periodically. i was thinking that the speakers were so positioned that an echo within the room created a standing wave that destructively interfered making the amplitude drop. ... but then why isn't there constructive interference too? i'm sorta worn out, and i'm afraid i mightn't have explained things very well. help is appreciated though. i attached some graphs i made on-the-fly, just so you can see what i've been murmuring about.