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The cowbell in question: http://www.youtube.com/watch?v=OuU0BzXm-qk

In most cowbells, the larger the metal dome, the lower the frequency produced. What would cause a phenomenon where the opposite is true: the larger dome creates a higher-pitched sound, as the one in the video does.

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Without close inspection of the bell it's anyone's guess. I note the lower sounding bell sounds a bit muffled, so I'd guess it has a crack in it - possibly on the underside where we can't see. A crack can make a bell less rigid so it oscillates more slowly. An example of this is the Liberty Bell, which has a lower tone since it cracked.

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The thickness of the bell walls has an effect on the effective pitch of the bell. Thicker walls = more mass density = lower pitch (just like in guitar strings).

Also note that the diameters of the bells' lips are about the same (or at least not radically different). One of the important aspects of oscillations in a bell is that there is a standing wave around the circumference of the bell. This aspect of the oscillation is more important than the fact that the larger bell is primarily larger in terms of length from base to lip.

My hypothesis is that both bells were forged from similar sized pieces of metal; the larger one has thinner metal because the plate has been "stretched" out more.

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  • $\begingroup$ stiffness increases with thickness$^3$ mass increases with thickness, the thicker bells should have higher pitches, not lower. In guitar strings the restorative forces is due to tension which is independent of thickness, but a bell's restorative force is from the elastic deformation on the surface, and thus the stiffness is proportional to the restorative force. $\endgroup$
    – Rick
    Oct 20, 2015 at 11:47

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