Tool · Acoustics

Spatial Active Noise Control Simulator

A sound wave crosses a 2 m × 2 m plane. A ring of loudspeakers, or a straight active barrier, tries to create a quiet zone inside it. Switch ANC on, change the strategy and watch the field settle. The physics is a 2D acoustic FDTD solver running live in your browser.

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Error mics

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Quiet zone

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Outside zone

Attenuation = level without ANC / with ANC. Outside zone: change between loudspeakers and reference mics (positive = spillover, 0 = transparent).

View

Display: steady 0.4 Hz oscillation (phase-locked) · physics: 4 wave periods/s · 60 FPS · 12 FDTD steps/frame · grid 200×200 (1 cm/cell) · Δt ≈ 14.6 µs

Reference micsSecondary loudspeakersError micsQuiet zoneHover the field to read the level

Level at the cursor (dB)TotalNoise alone

Recorded while the cursor moves over the field (last 20 s). 0 dB = noise level in the zone without ANC. The gap between the two lines is what ANC removes at that point.

1. The noise

Noise frequency400 Hz · λ ≈ 86 cmSource angle200° · r = 66 cm

2. The zone to protect

Geometry

Closed ring of loudspeakers around a quiet zone in the centre.

3. The control method

4. The loudspeakers

Spacing16 loudspeakers · d = 11 cm = 0.13 λ

Type

What the three strategies do

Silence only is a narrowband multichannel LMS controller (FxLMS at one frequency). It uses a model of the paths from each loudspeaker to each microphone, and drives the loudspeakers so the error microphones hear as little as possible. The quiet zone appears, but the loudspeakers also radiate outwards: the noise gets louder elsewhere.

Silence + transparency adds a second goal: predicted radiation on an outer ring must stay low too. With simple monopole loudspeakers the two goals fight. With monopole + dipole pairs (Huygens sources) both can be met.

Exact Huygens is the textbook limit: a continuous layer of monopoles and dipoles on the array, driven by co-located pressure and velocity probes (Kirchhoff-Helmholtz theorem). Inside, the field is cancelled; outside, the wave passes as if nothing were there.