Passive DIY Metal Hydrophone Underwater Acoustic Probe
A challenging, hands-on discovery and STEM project designed for curious young minds aged 10 to 14.
Materials Needed
- • 27 mm piezoelectric ceramic element disc (1 unit)
- • Shielded 3.5 mm aux microphone cable (or old earbuds with mic) (1 unit)
- • 100% silicone waterproof sealant (clear) (1 tube)
- • Smartphone or portable voice recorder with headphones (1 set)
- • Natural pond, stream, or deep bucket of water (outdoor access)
Pro Tips
- → Solder or twist the leads of a piezo disc element to an aux cable and coat all exposed metal in waterproof silicone.
- → Water is roughly 800 times denser than air, transmitting sound waves four times faster.
- → Lower the waterproofed hydrophone into a garden pond or bucket: clinking pebbles or swimming fish produce clear audio through headphones.
Safety First
Ensure silicone seals are fully cured and waterproof before submerging; keep phones away from water edges.
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Step-by-Step Instructions
Step 1
Solder or securely splice the two wires of a raw 27 mm piezoelectric disc to the microphone/ground lines of a 3.5 mm audio cable.
Step 2
Coat the entire piezo disc and bare solder joints in a smooth layer of waterproof silicone sealant, allowing it to cure completely.
Step 3
Plug the cable into a smartphone or portable audio recorder equipped with wired monitoring headphones.
Step 4
Lower the hydrophone into a pond or bucket of water, tap the container edge or drop pebbles, and listen to the clear underwater audio.