High frequency dog bark controllers, or "dog whistles," work to control your dog because dogs can hear pitches well above human range. While the average human's hearing capacity maxes out at about 23 kHz, a dog's can go all the way up to 45 kHz, according to Louisiana State University. Building a high frequency dog bark controller means producing a whistle that emits noise in the 24-45 kHz frequency range.
Saw both ends of the large piece of wood to create flat surfaces, if necessary.
Bore a hole about 1 inch deep into one end of the wood. This will create a hollow ring on one end.
Cut a notch into the wood above the hole. Saw perpendicularly along the shaft until you hit the bored hole. Then saw at a 45 degree angle 1/4 inch farther down the shaft so that you intersect with the first cut right around the bore.
Cut a second piece of wood so that it slides into the bored hole.
Cut the second piece of wood to match the exact length from the tip of the bore to the notch.
Shave off one side along the length of the second piece so that it is no longer quite a cylinder. This will create the small air space in the bore, creating the high frequency sound. Be conservative here. If you shave too little, you can always shave more. If you shave too much (to the point where a human can hear the whistle), you will have to start this step over.
Slide the second piece of wood into the bore hole. The fit should be tight enough that you do not need any adhesive. Make sure the shaved edge is at the top, lined up with the notch.