Acoustic Camera: What It Is and How It Works

An acoustic camera is an instrument that locates sound sources and shows them as a colour map over live video. Inside it has an array of dozens of MEMS microphones, an optical camera and software that calculates where the sound comes from using the difference in arrival time at each microphone. This makes leaks, electrical discharges and noisy mechanical components visible.

What an acoustic camera consists of

According to Crysound, an acoustic camera combines three parts:

1. Microphone array. Typically from 64 to more than 200 MEMS microphones arranged in a circle, spiral or grid. Crysound classes 64 microphones as entry level and 128 as professional grade.
2. Optical camera that records video of the scene.
3. Processing software that builds a map of sound sources and overlays it on the video.

For example, the SDT SonaVu has 112 digital MEMS sensors, a sample rate of 96,000 samples per second and an image refreshed at 25 frames per second on a 5-inch touch screen. The Crysound CRY2620 has 64 MEMS microphones in a 12 cm array; the CRY2623 has 128.

How the camera finds the source: beamforming

Sound from a source reaches each microphone of the array with a slightly different delay because the distances differ. The software then works as follows:

1. For each point in the field of view it calculates the delays with which sound from that point would reach each microphone.
2. It shifts the signals of all channels by those delays and sums them.
3. If there really is a source at that point, the signals add up and the sum is large. For other points they partly cancel.
4. It repeats the calculation for every point in the frame and obtains an intensity map, shown in colour over the video.

This method is called beamforming. Crysound compares the result to a thermal camera: instead of hot spots, the screen shows loud spots.

The array geometry sets the frequency limits. The low-frequency limit is governed by the overall array diameter: the larger the array, the lower the frequencies it resolves. The high-frequency limit depends on microphone spacing: the closer the spacing, the higher the frequency before spatial aliasing occurs.

Why the camera listens to ultrasound

According to SDT, leaks, partial discharge and steam traps create turbulence, and turbulence produces ultrasound that travels through the air.

Typical frequency ranges by task according to Crysound:

Task	Typical range
Compressed air leaks	20–50 kHz
Partial discharge	20–100 kHz
Mechanical faults	1–20 kHz

A camera limited to 20 kHz is suitable only for audible noise analysis. SonaVu provides filtering by a selected frequency range and image averaging, so the operator isolates the band in which the target source sounds.

What tasks an acoustic camera handles

Task	What the operator sees	According to the manufacturers
Compressed air, gas and vacuum leaks	The leak point on a pipe, fitting or valve	The Crysound CRY2620 and CRY2623 estimate leak rate and cost; SDT produces reports and leak cost estimates in the InSights web app
Fugitive gas emissions	Leaks from high-pressure areas: pipes, valves	SDT lists this application for oil and gas facilities
Partial and corona discharge	The discharge location on switchgear, a transformer, an overhead line or a cable	The CRY2623 localises discharges, distinguishes surface, suspension and corona discharge and builds a PRPD pattern in real time
Steam traps	A working or failed steam trap	SDT lists them as sources of airborne ultrasound
Mechanical	Bearing wear, gearbox noise, leaking valves	Crysound places these tasks in the 1–20 kHz range

More on specific tasks:

• survey route and leak search procedure: How to Find Compressed Air Leaks in a Plant;
• ultrasonic partial discharge inspection: Partial Discharge in Switchgear and Substations;
• corona at substations: Corona Discharge at a Substation.

SonaVu stores images and video, which are used in the survey report.

Limitations of the method

• Resolution. Beamforming resolution is limited by wavelength and array size. Angular resolution depends on frequency and distance, and a larger array separates closely spaced sources better.
• Distance. Beamforming is designed for the far field, roughly from 1 m. Detection range depends on leak size, background noise, microphone count and frequency range. Crysound estimates that a typical handheld camera sees a 1 mm compressed air leak from 10 to 30 m.
• Background ultrasound. In a noisy plant the source is harder to isolate. SDT recommends setting camera sensitivity to the background level in the area being surveyed. More microphones give better noise rejection.
• Outdoor sites. According to Crysound, outdoor work requires wind noise rejection and a weather-resistant design.
• Hazardous areas. A certified version is required, such as the SonaVu ATEX or CRY2624 ATEX.
• Interpretation. The camera shows where the sound source is, but classifying partial discharge and complex patterns requires operator training.

Example specifications

Parameter	SDT SonaVu	Crysound CRY2620	Crysound CRY2623
Microphones	112 MEMS	64 MEMS	128 MEMS
Frequency range	1–47.5 kHz	2–40 kHz	2–48 kHz
Distance	0.3–50 m	0.5–70 m	0.3–120 m
Screen	5", 800 × 480	7", 1024 × 600	7", 1024 × 600
Weight	1.2 kg	1.7 kg	1.7 kg

Specifications are taken from official SDT and Crysound materials. Which camera fits a given task and budget is covered in SonaVu or Crysound: Which Acoustic Camera to Choose in 2026.

Which instrument to choose

• Leaks, electrical and mechanical inspection with one instrument, reports in InSights: the SDT SonaVu.
• Leaks and partial discharge with PRPD and leak cost estimates: the Crysound CRY2623.

KEG TRK supplies SonaVu and Crysound acoustic cameras in Kazakhstan. Price on request.

Sources

• Crysound. Acoustic Camera: How It Works, Types & Applications.
• Crysound. CRY2620 64-Mic Industrial Acoustic Imaging Camera.
• Crysound. CRY2623 128-Mic Industrial Acoustic Imaging Camera.
• SDT Ultrasound Solutions. SonaVu Acoustic Imaging Camera.
• SDT Ultrasound Solutions. SonaVu Brochure (PDF).