Dual Microphone Array Design: Phase Difference, Beamforming & Engineering Trade-offs

In Part 1, we introduced the fundamentals of microphone arrays and beamforming.
Now, we move into the engineering core—how a 2-microphone (dual-mic) array actually works, and why it remains the foundation of most modern voice systems.

Despite its simplicity, the dual-mic array reveals nearly all the critical principles behind advanced array architectures.

Why Start with a 2-Microphone Array?

A microphone array can consist of dozens—or even hundreds—of elements.
However, every complex array can be reduced to interactions between pairs of microphones.

This makes the dual-mic array the fundamental building block for:

• Smart speakers
• AI voice modules
• Wearables
• Automotive voice systems

At SISTC, many optimized solutions begin with dual-MEMS microphone architectures, then scale into multi-channel arrays.

👉 Explore our MEMS microphone portfolio:
https://sistc.com/product-category/mems-microphone/

The Key Concept: Phase Difference

When a sound wave reaches two microphones placed at a distance D, it arrives at slightly different times.

This creates a phase difference, which determines whether signals:

• Reinforce each other (constructive interference)
• Cancel each other (destructive interference)

What affects phase difference?

• Microphone spacing (D)
• Sound frequency (λ)
• Arrival angle (θ)
• Applied delay (τ)
• Phase inversion (ρ)

This relationship is the core mechanism behind beamforming.

Two Fundamental Array Types

Dual-mic arrays can operate in two main modes:

1. Additive Array (Summation Mode)

Working principle:

• Signals are added together
• Optional time delay aligns signals from a target direction

Characteristics:

• Flat frequency response (on-axis)
• Strong signal gain
• Directionality depends on frequency

Typical configurations:

• Broadside array
• Endfire array

2. Differential Array (Subtraction Mode)

Working principle:

• One signal is inverted and subtracted
• Output = difference between microphones

Characteristics:

• Strong directionality even at low frequencies
• Built-in noise suppression
• Limited bandwidth (low-frequency roll-off + high-frequency aliasing)

Broadside vs Endfire: Directional Behavior

Broadside Array

• Maximum sensitivity perpendicular to mic axis
• Symmetrical pickup pattern

Endfire Array

• Maximum sensitivity along the mic axis
• Strong forward focus

👉 Endfire arrays are widely used in:

• Smart speakers
• Voice assistants
• Automotive cabins

From Omni to Cardioid: Pattern Formation

By adjusting delay and phase, dual-mic arrays can create classic directional patterns:

These patterns are essential for voice isolation in noisy environments.

SNR Improvement in Dual-Mic Arrays

A key advantage of dual-mic arrays is SNR enhancement.

When signals align:

• Signal power increases by +6 dB
• Noise power increases by +3 dB

👉 Net improvement:
+3 dB SNR gain

This is critical for:

• Far-field voice pickup
• Low-power AI devices
• Edge computing systems

The Trade-offs Engineers Must Consider

Designing a dual-mic array involves multiple trade-offs:

1. Microphone Spacing (D)

• Larger spacing → better directionality
• But → earlier spatial aliasing

2. Frequency Dependency

Additive arrays:

• Lose directionality at low frequencies

Differential arrays:

• Maintain directionality
• But suffer from bandwidth limitations

3. Noise Sensitivity

Differential arrays:

• More sensitive to mismatch between microphones
• Require precise calibration

4. Implementation Complexity

Adding:

• Time delay
• Phase control
• Gain weighting

increases system complexity—especially in real-time AI applications.

How SISTC Optimizes Dual-Mic Performance

At SISTC, we go beyond basic array design by integrating:

✅ High-consistency MEMS microphones

• Tight sensitivity matching
• Low self-noise

✅ Advanced noise reduction algorithms

• Adaptive filtering
• AI-based voice enhancement

✅ Hardware + software co-design

• Signal conditioning circuits
• Embedded processing modules

👉 Explore our integrated solutions:
https://sistc.com/product-category/sensor-module/

Real-World Applications

Dual-mic arrays are widely used in:

• Smart home voice control
• Bluetooth headsets
• Automotive voice systems
• Industrial voice interfaces

They provide an optimal balance between:

• Performance
• Cost
• Power consumption

Conclusion

The dual-microphone array is the foundation of modern beamforming systems.

By leveraging:

• Phase difference
• Time delay
• Signal subtraction

it enables:

• Directional audio capture
• Noise suppression
• Efficient voice interaction

In the next article, we will explore how multi-element arrays (N-mic systems) dramatically enhance performance—and what it takes to design them effectively.

References

1. Analog Devices application note AN-1328, available at https://www.analog.com/media/en/technical-documentation/application-notes/AN-1328.pdf [accessed June 2021]. Describes principle of operation, design, and construction of professional grade studio or live performance microphone using up to 32 analog MEMS microphones connected to op amps and a difference amplifier. Design is a volumetric array consisting of two additive broadside arrays in a differential end-fire configuration.
2. TDK InvenSense applicaton note AN-1140, available at https://invensense.tdk.com/wp-content/uploads/2015/02/Microphone-Array-Beamforming.pdf [accessed June 2021]. Discusses basic principles and performance of various array configurations.