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Here is an instrument that I made for science olympiad state and nationals last year. Take two pieces of balsa wood about 3 inches by 1 foot, streatch a rubberband lengthwise around one of the pieces of balsa wood and rubberband the ends of the balsa wood pieces together. You will need to play around with it a bit to find the correct notes but each note should be about 1/2 in apart depending on the humidity (the wood will expand and compress as the humidity changes, which will alter the notes slightly). My team came in 3rd at state and 53 out of more than 60 teams at naionals in sounds of music for this design. For more ideas you could also check out teh science olympiad homepage under the sounds of music page, division c events.
I forgot to mention that the design is for a harmonica, just blow into the opening between the two pieces of balsa wood to generate the sound. Also, you will need to put 2 rings of paper about 1/2 inch wide encircleing the piece of balsa wood widthwise underneath the lengthwise rubberband before rubberbanding the ends of both pieces of wood together. I found that it works better to glue or tape one of the pieces of paper down as far to one of the ends as you can so you only need to move one of the pieces of paper to change the notes. Blow in between the pieces of paper to get an accurate note.
Sorry it is so confusing.
If you need a picture, just search wooden harmonia in google images