Tunable single chamber ocarinas have existed for a long time, using a moveable plug to displace chamber volume. However I have never seen efforts made to apply this to multichamber ocarinas, double and tipple ocarinas. Although, it would have benefits to a player.
The pitch of an ocarina does not respond linearly to changes in blowing pressure over its whole range. The high notes are more sensitive than the low notes. In single chambers this is challenging, but additional issues arise in multichambers.
When a multichamber (in this case, a triple ocarina) is played at its original tuning temperature, the maker will have tuned the chambers so that they play with a progressive gradual increase, with no erratic change between chambers. On ocarinas designed to play harmonies, a slight decrease in pressure will exist, which I have shown here.
However when such an ocarina is played at a lower temperature, and the player blows the instrument up to concert pitch, the pressure required to sound the high notes of all of the chambers will increase. Thus the following chamber will start at a lower than expected pressure.
The opposite will happen when playing in a warmer environment, and an unexpected increase will be present between chambers.
An effective tunable multichamber ocarina would allow a player to return the breath curves to their original state, and bring back consistency in the pressure changes between chambers. It will also improve the instruments tone, as greatly under or overblowing notes tend to sound worse.
Creating a tuning mechanism that works on the first chamber shouldn’t be too difficult, as it is essentially the same as a single chambered ocarina. However, the higher chambers pose more of a challenge.
Inserting a tuning plunger into these chambers is going to cause problems, as the high chambers of a multichamber ocarina have a very small internal diameter. A tuning plunger within the chamber itself would shade, or even block some of the finger holes.
I can think of two ways of adjusting the tuning on the higher chambers of a multichambered ocarina, adjusting tuning holes, and introducing a secondary tuning volume.
The higher chambers of multichambered ocarinas almost always have tuning holes, which are used to improve the tone of the low notes of these chambers. The tuning holes could be used to adjust the tuning of the higher chambers if they were intentionally made oversize:
When I thought about ways of improving the effectiveness of tunable single chamber ocarinas, I proposed the idea of introducing tuning volumes. A tuning volume is a parallel tube, plugged with a moveable piston, which is attached to a chamber. This idea can be easily adapted to a multichamber.
As the higher chambers of a multi have no free space on their left hand end, the tuning plungers would need to be added to the right hand end of the chambers.
In order to correlate the tuning across the multiple chambers the plugs could be marked with graduations. These graduations would be spaced such that an equal number would need to show to match the tuning of all chambers.
I have explored the potential benefits of a tunable multichamber ocarina, and don't see anything fundamental that would prevent the idea from being implemented. It would be interesting to see how these ideas would work in the real world.