Wednesday, October 19, 2011

A Resonator Mystery

Over the years i have always been amazed by what we don't know , especially in an area where it seems we have advanced so far beyond, it would have be long figured out long ago.
 No such luck in many cases.
 While they are figuring out what they did wrong at CERN with their faster than light results, i have stumbled into something that should have long ago been dealt with.

While in the process of tuning up some instruments in a new tuning, i had some tubes that are to become resonators that i decided to play with a bit  on a set of reeds tuned to the same tuning. Terumi suggested playing with open resonators so i took the caps off and found i could augment the sound of a reed and use my hand to open and close to play with the sound. The problem was that the resonators were resonating a pitch a whole tone or more lower than what all the the theoretical measurements have been telling me.

 I checked my answers with others who concluded that what i had was in the the range of what they had. I asked on the reed organ list if anyone there had such a thing happen and one suggested that it was the cavity that held the reed that jointly made a lower resonator. This made total sense to me and assumed it was correct but i thought i could check it by trying it against the second set of reeds which has a much shallower cavity. the result was the same.
 One of the things i did to test was to play the pitch it should be along with the lower pitch.
 In all cases it is the lower pitch that sounded much louder.

It appears i am not the first to notice this. i got an message from Simon Buser,  a builder and Organist in Germany who said,

"The same system of reeds 2 semitones higher than the resonators I found in Organ Clarinets of Aeolian-Skinner. Seems to be the usual way to handle this phenomena: by experience, not by calculation, I suppose."

My own theory at the moments is that since they are suction reeds not blowing reeds that the suction lowers the air pressure. But still have to figure out a way to test this.
 Oh yes BTW with a vibraphone bar it works as expected.

Anyway one can have some musical fun with this as can be heard here. [Might take a minute to load]. The top pitch is the theoretical one and the lower is the one that works

1 comment:

  1. Kraig, I seen an experiment somewhere about blowing up a huge bag and it was easier to do by blowing in such a way that a pressure reduction inside the bag allowed air from outside to rush in instead of blowing up a lungfull at a time, My guess is that you could make different shapes on the entrance of the air cavity to enhance or reduce this effect.
    I want to put tiny propellors on the sound holes of my acoustic instruments haha. I found it by typing in Bernouli Bag, haha Billy