A HYDROPHONE FOR UNDER 90 DOLLARS THAT HEARS BELOW THE RANGE OF HUMAN EARS
Detect underwater sound below 20 Hz with a hydrophone you build for under 90 dollars - commercial reference hydrophones start at around 450 dollars before you add the measuring equipment.
by Nhut Thang Le, Van Tu Duong and colleagues (Ho Chi Minh City University of Technology)
ScienceOpen-hardware
Built with3D printing
- difficulty
- ●●●●○
- time
- a few weeks
- license
- CC BY 4.0
- repo
- repo FINISHED0 stars
●●●●○ · a few weeks · CC BY 4.0 · 0 stars · repo FINISHED
WHAT YOU’LL NEED
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COMPAREE VERDICT
This is a peer-reviewed low-frequency hydrophone from HardwareX: a piezoelectric ceramic disc in a 3D-printed ABS housing, sealed with elastic dip, copper-foil shielding and silicone, feeding a TL082-based high-impedance amplifier and band-limiting filter, powered by a ±12 V module. The whole device weighs about 500 g and costs under 90 dollars in parts. The authors showed it picking up a 20 Hz test signal in the lab, a clean 12 Hz signal in a test at Vietnam's defence metrology directorate, and the low-frequency emission of a biomimetic fish robot underwater. Be clear about what it is: a functional, low-cost detector for teaching and small labs - the authors say it has not yet been calibrated for sensitivity, frequency response or noise floor, and was only tested at lab scale. You read it on an oscilloscope (or your own data acquisition), and the paper puts fabrication at up to 100 hours. A great entry into infrasonic acoustics if you are comfortable with analog electronics.
IN THE REPO
GOOD TO KNOW
- —The paper is published under CC BY 4.0, which permits commercial use with attribution.
- —CAD files for the 3D-printed ABS housing are provided as supplementary data.
- —The bill of materials is itemised in the paper with supplier codes and costs.
- —The full Altium Designer project — schematic and PCB layout — is in the data repository, so you can order the board.
- —No firmware — this is a pure analogue amplifier chain feeding a data acquisition system.
- —The paper reads the signal on an oscilloscope and does not name a data acquisition device; for recording, pick one with good response below 20 Hz.
Parts to buy
8 itemsFrom our check of the build. Exact quantities and part numbers are in the creator’s BOM.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
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Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read the full paper (Open access; all the detail is in the methods section and the supplementary files.)
- 2.Download the supplementary data for CAD files and the detailed BOM (Download from the Mendeley Data repository (doi.org/10.17632/42mksnzmw2.2): schematic, Altium PCB project, BOMs and 3D files.)
- 3.Source the piezoelectric disc and op-amps first(The paper gives supplier codes; check lead time because ceramics can have long waits.)
- 4.Print the housing in ABS and test-fit the sensor before sealing(Once you seal it, disassembly is destructive.)
KNOWN ISSUES
- You need a readout device — the authors used an oscilloscope. If you want to log data to a computer instead, pick an interface with high input impedance and a sample rate that covers your band.
- The critical high-impedance stage is between the piezo disc and the amplifier - keep the 10 MΩ input resistor and short, shielded wiring there, or the low-frequency signal will be lost before it is amplified.
- ABS warps if you print it without an enclosure or heated bed. The housing needs to be dimensionally stable or the waterproofing will fail.
- The elastic dip and silicone seal must go on without voids or the sensor will flood. The paper describes the layering sequence in detail; follow it.
- The paper does not calibrate the sensor - the authors list calibrated sensitivity, frequency response and noise floor as future work. Out of the box you get a sensor that detects low-frequency signals; if you need absolute numbers, you must calibrate it against a reference yourself.
- Infrasonic validation in air is hard because you need a big speaker and a lot of power. The paper used underwater testing for a reason; plan accordingly.
Is this only for underwater, or can I use it in air?
The design is optimised for water. Infrasound in air is harder to generate for testing and the impedance match will be different. The paper does not cover air use.
What data acquisition system should I buy?
The authors read the output on an oscilloscope and do not specify a data acquisition device. If you want to record to a computer, any DAQ or audio interface that can handle sub-20 Hz signals (DC-coupled or with a very low cut-off) will do; check the low-frequency response in its datasheet.
Is there SMD soldering?
Yes, a little: the resistors are 0805 SMD parts and the diodes are SMD too, while the TL082CP op-amp is a through-hole DIP chip. The full Altium PCB project is published, so you can order the board as designed - 0805 parts are manageable with a fine iron and tweezers.
How do I calibrate it without a commercial hydrophone?
You cannot. Calibration requires a reference. If you are using this for relative measurements only — comparing one signal to another with the same sensor — you can skip absolute calibration, but you still need to validate that the frequency response is flat across your band.
What is the depth rating?
The paper does not give one. The housing is ABS and the seal is silicone; both will compress under pressure. This is a shallow-water sensor. Do not take it deeper than a few metres without testing.
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FROM THE COMPAREE TEAM
The paper shows it picking up the low-frequency swimming signal of a biomimetic fish robot underwater - what would you point yours at?
Nhut Thang Le, Van Tu Duong and colleagues (Ho Chi Minh City University of Technology)
A team led by Van Tu Duong at the Ho Chi Minh City University of Technology (HCMUT) published this design in HardwareX in 2026 to make infrasonic underwater measurement affordable for teaching and small research labs, where commercial hydrophones and their measuring equipment are too expensive.
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- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM27d agoedited
Practical notes from our verification: this is a HardwareX paper, not a GitHub repository; the source files are on Mendeley Data, including the 3D-printed housing and a complete Altium project with the PCB layout, so you do not have to lay out your own board. The amplifier is built around a TL082CP op-amp, and in the paper the output is read on an oscilloscope; for longer recordings you will want a data acquisition device that handles signals below 20 Hz. The authors put the hydrophone itself at under 90 dollars, not counting the readout instrument, and note that its power module runs from 220 V mains. Be aware of the stated limits: it was validated functionally at lab scale, without calibrated sensitivity or frequency-response data, so treat it as a teaching and prototyping instrument until you calibrate it yourself. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.