Wapu
Music plays a major role in the culture of the Tāngata people of Atu Motu. Traditional songs are a part of daily life, and most people learn to play several musical instruments. One instrument however is reserved for those who have been trained in ritual magic - this is known as a wapu.
A wapu is a piece of carved wood attached to a string. The wood is shaped so that when it moves through the air it produces a low roar that can be heard for great distances. This sound is somewhat reminiscent of an active wasp's nest, and wapu mean 'wasp' in Tāngatāiki. The player spins the wapu through the air, varying the speed to change the volume and pitch it produces. Additionally, the size and shape of the wapu can influence the final sound it produces, and a shaman may have several in their collection for different purposes.
The Tāngata believe that the sound of the wapu can be heard not just at a great distance, but that it transcends the physical realm and can be heard by the Atua, the spirits of Atu Motu. Shamans combine the wapu with specific traditional songs to summon particular spirits. It is most often used in rituals of healing, but it can also be used to influence the weather, ward off evil magics, or to seek guidance. In some instances, the spirit will seize control of the wapu in flight, pulling it (and the shaman playing the instrument) in some direction, to show the shaman where the spirit wishes them to go. In other instances, the wapu will be hung in the wind for the Atua to control, and the shaman interprets what music it makes in order to provide guidance to the people.
In recent years, some foreigners have begun to learn to play the wapu, not for its spiritual qualities, but as a tool for long distance communication. The low roar of the instrument can carry remarkably long distances, and can allow for effective communication between ships too far apart for shouted communication. While it is not displacing flag or lantern signaling, it is carving out a niche as another way ships can interact on the open waters.
That would be a wonderful sound to hear, and then different pitches too! I have a hard time visualizing it though. How is it shaped? What does the wood look like? Would it sound as deep as a didgeridoo?
I based it on the bullroarer, and more specifically the Māori pūrerehua - there are some good videos about this traditional instrument that will let you hear what it sounds like. It's a pretty cool sound.