[Antonio Freixas]

David,

Thanks for the discussion and the demo. Yes, it is very interesting that a highly pressurized bladder gives a sour note or sometimes causes the reed to block.

Here’s my new theory. The bladder can be used to control the air chamber pressure; in general, the more inflated, the higher the pressure (studies on balloons says that this is not strictly true–pressures in a balloon can rise during its final shrinkage phase and then drop again–but it’s true as a general trend).

The bass reeds don’t do well with too little or too much. This is actually true for a lot of reeds–they can be optimized for low airflows and high airflows. To make them work well for both, I’ve heard that some reed makers add a slight bevel to the reed plate hole, but that’s another story.

Now, for a comparison with rigid air chambers. Rigid air chambers can also provide a range of pressures, I would think, depending on how hard you blow. I just tried my Hammond 44H. If I pressurize the chamber as much as I can and press a key I hear…nothing.

So the difference between a bladder and rigid air chamber, is that the former resists pressure drops (and increases) longer and that this attribute is needed to get the reeds to sound. It might also be needed to keep them sounding. To really verify this would take some work.

The simplest physical model would be a tube with a balloon inserted in the middle. There is a lot of literature on flows through tubes, but I don’t know of any where the tube has expanding walls. Oddly, I asked this question on the Physics Forums site when I was exploring the physics of flexible mouthpieces. I learned a few things, but didn’t get an answer I could use in this situation.

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