How Many Microphones Does an Acoustic Camera Need for Industrial Inspections?

Why Microphone Count Matters

The number of microphones in an acoustic camera is the single most important specification for determining its performance. More microphones means better spatial resolution (the ability to distinguish two nearby sound sources), longer detection range, and better performance in noisy environments.

The relationship between microphone count and performance follows a predictable pattern: doubling the number of microphones approximately doubles the signal-to-noise ratio improvement from beamforming (a 3 dB gain), and reduces the beamwidth — the angular resolution — proportionally.

However, more microphones also means higher cost, more data to process, and typically a larger physical array. The right microphone count depends on your specific industrial application, facility size, and typical detection distances.

Unitech Tools offers acoustic cameras at three performance levels: the SW136 with 136 microphones in a compact form, the GSW Series with 136 microphones in a full-featured design, and the FA611S fixed system with 136 microphones for continuous monitoring.

"Don't assume more microphones is always better. A 64-channel camera may be perfectly adequate for a small plant, while a 136-channel camera is essential for outdoor substations and large facilities. Match the camera to your real-world conditions." — Field Application Engineer, Unitech Tools

64 Microphones: Entry-Level and Close-Range

Acoustic cameras with 64 microphones represent the entry level of professional acoustic imaging. They offer adequate performance for close-range inspections (up to 10-20 meters) in relatively quiet environments.

Typical applications for 64-channel cameras:

• Small compressed air systems in workshops or light manufacturing
• Classroom/training environments
• Basic R&D or educational demonstrations
• Low-budget initial leak detection programs

Limitations: A 64-channel camera has a beamwidth of approximately 5 degrees, meaning at 10 meters it can only distinguish sound sources that are about 87 cm apart. In a substation where you are trying to identify which specific bushing on a transformer is producing PD, this resolution is insufficient. The limited number of microphones also means the beamforming algorithm has fewer degrees of freedom to cancel ambient noise, making these cameras less effective in noisy industrial environments.

For most industrial and power utility applications, 64 microphones is not recommended — the spatial resolution and detection range are simply too limited to deliver reliable results.

96 Microphones: The Mid-Range Standard

Acoustic cameras with 96 microphones represent the sweet spot for many medium-sized industrial facilities. They offer good performance at distances up to 20-50 meters with a beamwidth of approximately 3 degrees.

Typical applications for 96-channel cameras:

• Medium-sized manufacturing plants (500-5,000 m2)
• Indoor substations and switchgear rooms
• Compressed air leak survey programs
• Steam trap inspection
• Vacuum leak detection in packaging plants

A 96-channel camera provides a good balance of cost and capability. The 3-degree beamwidth allows discrimination of sound sources approximately 52 cm apart at 10 meters — adequate for identifying specific pipe sections or panel zones, but not enough to pinpoint individual components.

For facilities just starting an acoustic imaging program, a 96-channel camera offers a reasonable entry point. However, many users find that they quickly outgrow this capability and upgrade to a higher-channel-count system for more demanding applications.

136 Microphones: Industrial-Grade Performance

Acoustic cameras with 136 microphones deliver the highest practical performance for industrial and utility applications. With a beamwidth of approximately 1.5 degrees and detection range up to 80 meters, these cameras provide professional-grade results in demanding environments.

Typical applications for 136-channel cameras:

• Large industrial plants (5,000+ m2)
• Outdoor high-voltage substations (69 kV to 500 kV)
• Gas-insulated switchgear (GIS) SF6 leak detection
• Transmission line corona inspection
• Partial discharge detection in transformers and switchgear
• Critical infrastructure continuous monitoring

The GSW Series from Unitech Tools features a 136-microphone MEMS array specifically designed for these demanding applications. The 1.5-degree beamwidth means it can distinguish sound sources just 26 cm apart at 10 meters — enough to identify which specific termination on a switchgear panel is producing PD.

The SW136 handheld offers the same 136-microphone capability in a more portable form factor, while the FA611S fixed system provides 136-channel performance for 24/7 permanent installation with automated alarm capabilities.

"We upgraded from a 64-channel to a 136-channel system and immediately saw the difference. With the GSW Series we can stand 30 meters from a substation and identify PD on individual transformer bushings. The 64-channel system simply couldn't do that." — Maintenance Superintendent, Colombian power utility

Microphone Count Comparison Table

For power utilities and large industrial facilities in Latin America, the 136-channel configuration is strongly recommended. The additional spatial resolution and detection range directly translate to more accurate surveys, fewer missed defects, and better ROI on the inspection program.

Matching Microphone Count to Your Application

Here is a practical decision framework for choosing the right microphone count:

Notice that the most critical applications — partial discharge detection, substation inspection, and SF6 leak detection — all recommend 136 microphones. This is because these applications require high spatial resolution to pinpoint the exact location of a defect, and the distances involved often exceed 20 meters.

In Latin America, where many utilities operate aging substations with mixed-technology equipment (AIS, GIS, hybrid), the 136-channel GSW Series provides the versatility to handle all inspection scenarios with a single instrument.

Other Specs That Matter (Beyond Microphone Count)

While microphone count is the most important specification, it is not the only factor that determines real-world performance. When comparing acoustic cameras, also consider:

• Frequency range: A wider frequency range (e.g. 2 kHz to 100 kHz) captures more types of defects. The GSW Series covers 2-100 kHz, including low-frequency mechanical sounds that high-pass-filtered designs miss.
• Array geometry: Spiral arrays (used in the GSW Series) provide more uniform spatial resolution across the field of view than rectangular or linear arrays.
• Processing speed: Higher frame rates (10+ fps) allow detection of intermittent events like intermittent PD.
• Optical camera quality: A high-resolution optical camera (12 MP in the GSW Series) provides clearer context for the acoustic overlay.
• Software features: Look for spectrogram display, automated leak quantification, and report generation.
• Environmental rating: IP54 for handheld, IP65 for fixed. Outdoor substation use requires weather-resistant equipment.

For comprehensive substation inspection, consider combining the GSW Series acoustic camera with the Hammer II thermal camera and the SC Series PD detector for a complete condition assessment toolkit.

Frequently Asked Questions

Is a 64-channel acoustic camera good enough for PD detection?

Generally, no. PD detection requires high spatial resolution to pinpoint the exact location of the discharge. A 64-channel camera's 5-degree beamwidth means you can identify a specific panel but not the specific termination or bushing within it. For PD detection, 136 channels are recommended.

Does more microphones always mean better?

Not always — there is a law of diminishing returns. Moving from 64 to 136 microphones provides a dramatic improvement. Moving from 136 to 192+ microphones provides incremental gains that may not justify the additional cost for most industrial applications.

Can I upgrade a 64-channel camera to 136 channels later?

No. The microphone array is a fixed hardware component. You need to purchase a new camera. This is why it is important to buy a camera with sufficient channels for your current and anticipated future needs.

How do I know how many microphones I need?

Consider your maximum detection distance and the smallest target you need to identify. If you need to pinpoint a 5 cm component at 20 meters, you need at least 136 microphones. For larger targets at close range, 96 may suffice. Contact Unitech Tools for a free application assessment.