My partner Hana and I wanted to create something that would encourage cooperation and playfulness in a personal setting. We knew we wanted to work with sound because it is easily noticeable by users and can be layered and varied to create interesting outputs. While thinking about all these things, we gathered inspiration from the Sidewalk Harp, by Jen Lewin, and the Music Bench, by Isabel Paez and Maya Tal. We liked how elegant the interaction was with the Sidewalk harp but wanted to create an interaction with collaboration and experimentation much like the Music Bench. 
The result was a two person interactive box with each side having two range sensors. The two people stand opposite from one another and move their hands away or towards the sensors to control the pitch of different instruments depending on the sensor. There is one switch per sensor, allowing users to toggle between instruments to create a diverse overall sound. Since the motion to control the pitch is natural and the sounds are distinct, the two users can easily explore different sounds to either create a balanced or chaotic soundscape.
The main pieces of hardware we used to create this object were an Arduino Uno and music instrument shield. The main user input is through the ultrasonic range sensors. The distance they record get mapped to a certain value to control the pitch. There are maximum and minimum bounds where no sound will play, so sound only plays when the users are present. In addition to sound, we included lights as an affirmative signal to user input. The range values get sent through the music shield which handles the sound generation for us. We used an aux cable to output the sound from a speaker. We soldered these circuits and enclosed it in a laser cut wooden box. Note that the box is shaped to emphasize the two person interaction.