This would be great but as Adam says different materials, masses and densities absorb/deflect sound differently. To model the conditions with any accuracy there has to be a way to express the sound attenuation effects of actual materials. This would be very useful for testing acoustic insulation but it sounds very complicated to achieve. Also sketchup deals with surfaces not solids, I'm presuming its easier in a solid modelling application to model acoustics. edit: You could group some geometry that represents, say, a concrete wall and then calculate the acoustic properties by its volume.