Wood is difficult if not impossible to contour to the new round shape. It would require the use of internal bracing and reinforcing members, and, as in conventional guitars, these members would act as baffles, substantially dampening and absorbing the sounds, and setting up non-repetitive vibration patterns which the human ear hears as noise. A guitar top must vibrate to help amplify tone. To vibrate properly, it must be extremely thin and thin wood is, of course, fragile. Sound, like light, reflects best from a smooth surface, and wood is porous. The cellular structure of wood and the natural oils in it vary considerably, not only from one guitar to another, but within a single instrument. The varying densities thus created make it extremely difficult to achieve consistent vibrating characteristics.