What sounds does acoustic leak detection equipment listen for?

Full transcript

George and Dave in conversation. Every word of the episode, exactly as recorded.

George

Welcome back to the show. I'm here with Dave from ADI Leak Detection, the UK's leading leak detection specialists, who's here to answer your questions and provide expert leak detection advice. Today's question is one I reckon a lot of homeowners have wondered about: when an engineer turns up with acoustic leak detection equipment, what is that device actually listening for?

Dave

It's a great question because most people picture some kind of magic wand. The honest answer is that acoustic leak detection equipment listens for the sound that pressurised water makes when it's forced through a crack, a failed joint, or a pinhole in a pipe. That sound travels through the pipe wall, through whatever's around it, soil, concrete, screed, and up to the surface.

George

So there's actually noise coming up through my floor from a leaking pipe?

Dave

There is, yes, though you'd never hear it with your ears. The frequencies we're picking up are often well below what humans can detect unaided. Acoustic leak detection equipment amplifies those frequencies so the engineer can actually hear what's happening under a solid floor.

George

What does it sound like? Is it a drip, a rush of water, something else?

Dave

It varies. The classic sound is a hiss, that's the friction noise water makes as it's pushed through a restriction under pressure. You also get what we call structural vibration: the pipe itself resonates, and that resonance travels through the surrounding ground. A bigger leak under higher pressure produces a more intense, broader signal. A tiny pinhole on a low-pressure supply line can be almost inaudible even through the equipment, so the engineer has to work very systematically.

George

Does the material the pipe's made from change what you pick up?

Dave

Significantly. Copper and steel carry sound really well along the pipe itself, so acoustic signals travel further before they fade. Plastic pipes, MDPE on a supply line, for instance, absorb a lot of that vibration rather than conducting it, so the signal drops off faster. That changes where the engineer positions the ground microphone and how they interpret what they're hearing.

George

You mentioned a ground microphone. Is that different from the main listening device?

Dave

The two work together. A listening stick or acoustic listening rod lets the engineer make direct contact with a stop tap, a meter housing, or an exposed pipe to hear the leak noise conducted through the pipework itself. Ground microphones then go onto the surface, onto a concrete floor, a path, a driveway, and pick up the signal radiating upward through the ground. ADI engineers use both to narrow the search zone down progressively.

George

How do they know they've found the right spot rather than just traffic noise or someone running a tap upstairs?

Dave

Background noise is a real challenge, especially in a terraced house or near a road. Acoustic leak detection equipment filters by frequency, background noise and vibration from traffic sits in a different frequency range to a pressurised water leak. The engineer also correlates: they take readings at several points along the pipe and the software calculates where the noise is loudest relative to the pipe's known length and material. That correlation pinpoints the leak position to within a few centimetres in most cases.

George

So correlation is a separate piece of kit on top of the acoustic equipment?

Dave

It is. Acoustic correlation uses two sensors placed at different points on the pipe, either side of the suspected leak zone. The sensors record the sound simultaneously and the correlator calculates the time delay between the two signals. Because sound travels at a known speed through a given pipe material, that time delay converts directly to a distance from each sensor. ADI engineers use correlation alongside acoustic listening as a cross-check, particularly when a pipe runs under a long concrete floor or a driveway.

George

That's really clear. So the acoustic equipment is essentially doing two jobs: giving the engineer something to listen to, and feeding data into a calculation.

Dave

Exactly right. The listening phase tells the engineer there's a leak present and gives them a rough zone. The correlation phase locks down the precise position. Getting both right means the team can make a single, accurate excavation rather than digging up half a floor looking for something that could be anywhere.

George

Dave, that's genuinely fascinating, I had no idea there was that much science in what looks like a fairly simple piece of kit. Thanks for breaking it down so clearly.

Dave

Pleasure. The kit's only as good as the person using it, mind. Reading an acoustic signal under a Victorian suspended floor is very different to reading one under a modern concrete slab, so experience matters as much as the equipment.

George

Well said. If you've got a hidden water leak you need traced, ADI Leak Detection are among the most trusted and experienced specialists in the UK, well worth getting in touch. We'll be back with more questions answered next time.

How this episode was made. This episode was produced using AI-generated voices and script, based on real leak detection questions and the working knowledge of ADI Leak Detection engineers. More about how the podcast is made.