My percussion quartet Locomotion calls for nine boos, which are wooden tongue drums.

See Musical Instrument Design: Practical Information for Instrument Making by Bart Hopkin for information on the construction of boos. Quoting Hopkin, "Boos are an important variation on tongue drums. Harry Partch gave the name boos to a set of vibrating tongue instruments he made of bamboo; I am taking the liberty here of expanding the term to include a host of similar instruments made from other materials."

Construct the boos in the form of rectangular wooden boxes that are closed at one end and open at the other, and with a tongue cut in the open end. The following example illustrates the procedure.

• Use any 1" x 6" lumber for the sides and back.
• Use any 1" x 8" lumber for the bottom and 1" x 8" hardwood for the top.
• Lengths ranging from 38" to 8" will result in pitches from approximately E2 to E4.
• Fasten the pieces into a box. Caulk all joints to ensure there are no air leaks.
• The cavity of the box will have a resonant frequency. You can hear this pitch by tapping the closed end on a hard surface or singing into the open end and noting which pitch is reinforced.
• Measure a 4" wide tongue on the top at the open end. Mark a length that varies from approximately 1/3 the length of the box on the longest drum to 1/2 the length on the shortest.
• Begin cutting the tongue, stopping at approximately half the measured length. Check the pitch of the tongue with a mallet. It should be significantly higher than the pitch of the box.
• Cut the tongue further in increments, checking the pitch after each cut. The pitch of the tongue will become lower as it gets longer. The pitch of the box may rise as you cut further, so check it as well. Cut in smaller increments as the pitch of the tongue gets near the pitch of the box.
• Carefully continue cutting, stopping while the pitch of the tongue is still slightly higher than the pitch of the box. The resonance of the box should now reinforce the pitch of the tongue and provide sustain.
• Note that as the pitch of the tongue gets close to the pitch of the box it is easy to misjudge which pitch is which and cut too far. Consider stopping while you are sure the pitch of the tongue is still higher than the box. You can fine tune each drum later as you gain experience.

Locomotion does not call for specific boo pitches, though the pitch range given above (E2 - E4) is recommended. If you would like to create boos with specific pitches, the following information can be used. Note that this is approximate and will likely only get you within a half step of your desired pitch.

A boo is a rectangular box closed on one end and is similar acoustically to a cylinder closed on one end. A closed cylinder has resonances approximately at the following frequencies:

or more accurately:

Solving for the length, and using n = 1 for the fundamental frequency:

Using 13,512 inches/second for the speed of sound and 6 inches as an approximate diameter (based on using wood that is 1"x6" for the sides and 1"x8" for the top and bottom), the length of a boo can be calculated as a function of the desired frequency.

More information is at Wikipedia.