[Antonio Freixas]

I, too, will resurrect this thread by replying to a post from almost a year ago.

The physics behind the little bladder hole in my Suzuki M37C is something I would definitely like to understand. I didn’t know the bass melodicas had bladders covering the entire air chamber!

Let’s look at the physics of balloons. Blow up a balloon and tie it off. The balloon, at this point, is neither growing nor shrinking. This tells us that the forces trying to make the balloon larger are equal to the forces trying to make it smaller.

The air pressure in the balloon is trying to make it bigger. The air pressure outside the balloon and the elastic potential of the balloon’s skin are trying to make it smaller. Therefore, the air pressure inside the balloon must be greater than the air pressure outside and it is greater by just enough to counteract the elastic.

So, in a closed system, anything stretchy increases air pressure. The stiffer the elastic, the higher the pressure.

Ok, that’s interesting but doesn’t seem to get us anywhere. If the stiffer the material, the higher the pressure, the highest pressures would be achieved with a material that was not elastic. At that point, the pressure would be whatever you could achieve with lung power.

If you have an open system, air becomes essentially incompressible, so it’s difficult to raise its static pressure (the pressure on the walls of the system). Think about what happens if you cut off the end of a balloon and try to inflate it. You can’t.

If you transition from a closed system to an open one, the elastic potential of the bladder will convert the static pressure in the air chamber into dynamic pressure (moving air–think about what happens when you release a filled balloon).

So here’s my guess: if you blow into the melodica when no keys are pressed, the pressure in the chamber goes up. When you press a key there is a large pressure difference between the top and bottom of the reed tongue. This should help get the reed moving. As you continue to sound the note, the extra pressure disappears and the reed now operates in the “normal” way (I’d have to explain the “normal” reed physics, which is complicated). The pressure in the chamber is probably about the same as the outside air. Lift the key and the pressure begins to build up again.

If my theory is correct, then if you play a note on the bass melodica, hold it for 1/2 second or so and then do a quick switch to another note, the second note may have a bit of problem getting started.

When I get a chance, I can try pressing on the bladder of my M37C to see if I can reproduce the “sour” note. Also, I’ll try to see if the bladder completely deflates when I hold a note. It may be that even in an open system, we can maintain a slightly higher pressure in the air chamber than outside. This would be surprising, but that’s how I learn things.

Anyone with a bass melodica can try the test I suggested. I’d be curious about the results. It would also be useful to check if the bladder deflates completely when playing a long note (I understand long notes are difficult on a bass melodica as the notes need a lot of air).