It exists already few models of tunable Tombaks. The one that I used for many years is designed by Master Hossein Omoumi.
Recently I designed my own Tunable Tombak using the air pump system. This tombak is available for sale.
The diameter is 26 cm (10 inches)
The Hight is 43 cm (17 inches)
Made in one piece of Mango Wood with Goat or Calf skin.
The opening (nafir) of the drum is little bit bigger than the traditional tombak, which gives a very nice deep bass sound (Tom). The inner design, makes also very sharp and clear Bak.
Tombak for sale. It can be shipped anywhere in the world. Contact me for more details : firstname.lastname@example.org