It's an article of faith among audiophiles that you can "hear" materials. It just stands to reason that, if a loudspeaker cone has a certain sound when tapped with a fingernail, then everything it reproduces will be colored by that sound. This is why an audiophile will tap the exposed cones of an unfamiliar loudspeaker to see what they sound like. But not every material has a characteristic sound; some aren't stiff enough to vibrate. A wet dishrag, for example, has no sonic "signature." Only if you hit something with it does it make any sound at all, and then it just goes splat. But any material stiff enough to push air without wilting is likely to have some kind of resonant mode that we can hear, so you just know that a metal loudspeaker diaphragm is going to sound metallic.