Week 9 – Forum – Tristan Louth-Robins - Singing Teapot

I must admit, I was expecting the teapot to sing similar to when a crystal glass sings when you run your finger around the rim. When I thought of resonating teapots, I had visions of having the teapot being vibrated by an outside frequency by sympathetic resonance (perhaps even by a sub or ultra frequency) and therefore giving off it’s own audible frequency. I was slightly disappointed because I was excited by my expectations, but it was interesting nonetheless.

I’d like to offer my opinion on the subject in case a few simpler ideas were overlooked. In a large room as Alvin Lucier experimented in it wouldn’t have been as big an issue, but forcing the sound back into the teapot (and probably most likely by the appearance of new overtones seen in later screengrabs of Peak) may be creating a pressure mode. A 200Hz wave is around 172cm which the teapot clearly isn’t but playing these frequencies into an area that can't reproduce them properly (and I know the argument will be that the teapot generated this frequency itself, but that frequency was originally recorded outside of the teapot in a room capable of reproducing 200Hz)will cause a buildup of frequencies below that point. They will then start to generate their own harmonics interfering with any sort of 'flat response' there might have been. There could also have been a standing wave present. A sphere is of course the perfect place for standing waves to thrive. Even though the teapot is not a perfect sphere, the widest part horizontally is perfectly round as far as I could tell apart from the area with the spout. Every opposite is exactly the same length on this axis and any resonant frequency would be reinforcing itself. 344/400 (double the length of the suspected standing wave) is 86cm. It just so happens that 5 instances of 17.2 = 86. This alone as far as I'm aware won't create a standing wave as the waveforms have to move past each other, and all this may be stretching things but it would be interesting to see if the inside of the teapot’s measurement was in fact 17.2cm. This would hide the actual resonance of the teapot structure and focus our ears on the resonance of the first standing wave of the teapot.

Noting the volume and keeping future passes through the teapot at that particular volume level would create a constance that would eliminate amplifying the standing wave and avoiding a pressure mode altogether allowing the true resonance of the teapot to sing. Come to think of it that may work nicely. If the original recording from the teapot was at say 20dB (or whatever), then play it back into the teapot at –3dB from that level. That way the original resonance is added to perfectly. The progress could be checked at intervals by amplifying the results so they could be heard at a decent level, but at least it should be free of artifacts and be a true resonance of the teapot. There’s also the addition of presence peaks from the mic and the amplifiers THD figures that need considering. Perhaps experiment with different mics, speakers, preamps and amplifiers as the fact that the tone landed exactly on 200 Hz seems odd to me. It’s not 197.3 or 204.7 for example but smack bang on 200Hz. Eliminating rogue frequencies would give a more acurate result. All this is from a slightly scientific point of view and if the whole aim is to simply make an instrument out of it then I’d say it works nicely as is.

Whittington, Stephen. 2007. Forum Workshop “Still and Moving Lines”. Forum presented at the University of Adelaide, 10th May.

Louth-Robins, Tristan. 2007. Forum Workshop “Still and Moving Lines”. Forum presented at the University of Adelaide, 10th May.