We definitely “have a thing” for electricity-free iPhone amps, and this lo-fi solution is made of PVC and an old bike horn! This is the absolute bees knees.

To make, get an old bike horn and remove the noise maker. Screw the horn into a piece of PVC aligned with the iPhone speaker. Be sure to learn the ends of the PVC open for more expansive sound. Now press play.

Source: lowtechatmo