It's a good question, and it points out that my statement was perhaps a little too bold. You can have a thing that resonates over a wide range of frequencies, but it will either have to be really big, or the resonance quality will be very low.windshieldbug wrote:What's a piano soundboard, then?Rick Denney wrote:There is no such thing as a broad-band resonator. In fact, it's a contradiction in terms
(And I ask that out of ignorance, not as the smart-*** I think I am... nor did any of that look close to such a device)
When you damp the vibrating piano string by lifting your finger, the large soundboard will continue to vibrate if undamped. It attenuates much faster than the string, which indicates much lower resonance quality. It trades resonance quality for broadbandedness. Compare it with the string itself, which when unstopped attenuates much more slowly.
The soundboard is a low-quality sympathetic resonator that couples with the vibration of the string to amplify it. It needs to be broadbanded so you don't have to tune it, and you don't want it to resonate very well or it would ring more on some notes than others and would continue to ring after you stop the excitation. So, you shape it funny to smooth out the resonance peaks.
A bass drum is a low-quality resonator, and it has to be big to resonate much at all. It's specifically untuned so that it doesn't resonate on any particular frequency, which means it's broadbanded. But even if you really whack it, it still only rings for a maybe a second.
Contrast that with a large tympanum. When the head is tuned to resonate well on a specific frequency, it will ring for a much longer time. But even tympani are low-quality resonators. Compare them with the tube under a vibraphone. Those tubes are really random-size resonators, and they work because they are big compared to the vibrations of the whatever-it-is-those-wood-things-are-called. Now, compare all those to chimes. Those are high-quality resonators, and they ring much longer than any drum head however carefully tuned. But as you move up this food chain, the longer ring accompanies the narrower range of frequencies.
Rick "suggesting that a pocket resonator might have a useful tuba-enhancing broadbanded resonance effect if it was the size of, say, Avery Fisher Hall" Denney
