Blade Count

★ = Lucas number (optimal)

Equal Spacing Prior Art

Acoustic Spectrum Sharp Tonal Peaks

— BPF Harmonic

High Peak Tonal SPL

1 Dominant Freq

Golden Angle · 137.508° Aureo Method

Acoustic Spectrum Distributed Broadband

— BPF Harmonic

−8 dB Peak Reduction

100+ Spread Freqs

Equal spacing creates a perfectly periodic blade pulse train — guaranteed to produce a concentrated tonal "whine" at the blade passing frequency and its harmonics. Every blade interaction arrives at a predictable interval; the acoustic energy concentrates into a few loud, psychoacoustically annoying peaks.

Golden-angle spacing (137.508°) is the mathematically most aperiodic arrangement possible. Successive blade positions never repeat and never cluster — proven by Diophantine approximation theory to be the slowest-converging rational approximant. The result: acoustic energy distributes across hundreds of frequencies, transforming the acoustic character from "whine" to "whoosh" with the same total power.

Blade counts marked ★ are Lucas numbers (3, 4, 7, 11, 18, 29…) — the only counts for which golden-angle spacing achieves its theoretical optimum with zero residual clustering. Lucas numbers include the practical count 4, which the Fibonacci sequence misses entirely.

Multi-Rotor Acoustic Decoherence

How Lucas blade-count diversity eliminates inter-rotor coherent reinforcement

Conventional

Aureo Optimized

Rotors

Distinct BPFs

Harmonic Overlaps

+7.8 dB

Coherence Penalty

Conventional (6 × 5 blades): All six rotors share the same blade passing frequency. At every harmonic, all six acoustic fields add with amplitudes — coherent power scales as N² = 36×, not incoherent N = 6×. This is a +7.8 dB penalty built into the design at the drawing board. The interference field above reveals concentrated standing-wave hot spots targeting the ground below the aircraft.

Conventional

Aureo Optimized

4 × 3B equal spacing · 1 BPF · +6 dB coherence penalty

3B · 60Hz

Ground Acoustic Footprint (directly below drone)

3B × 4

Blade Config

Distinct BPFs

+6.0 dB

Coherence Penalty

Harmonic Overlaps

Conventional quadcopter (4 × 3-blade equal spacing): All four rotors share the same blade passing frequency (60 Hz at 1200 RPM). Acoustic power scales as N² = 16× rather than N = 4× — a built-in +6 dB coherence penalty present in every standard quadcopter. The interference field below reveals concentrated standing-wave hot spots in the acoustic footprint directly below the drone.

AUREO ACOUSTICS

Sound Demonstration

Same power. Same blade count.
One you can't ignore. One you can.

Equal blade spacing concentrates all acoustic energy into one persistent tone. Golden-angle spacing spreads it across hundreds of frequencies. Listen to the difference — then hear what happens against urban background noise.

Select Platform Type

Delivery Drone
3B · 3600 RPM

Quadcopter ★
4B · 2700 RPM

eVTOL Rotor ★
7B · 1800 RPM

Industrial Fan ★
11B · 1500 RPM

Blade Passing Frequency: 180 Hz · Rotation: 45 Hz · ★ = Lucas number

Volume

Equal Spacing

360° ÷ 4 = 90° · periodic

Energy locked into
one pitch — unavoidable

Tonal Whine

Clear pitch · ear locks on · cuts through ambient

Spectrum Sharp harmonic comb ↑

180

BPF (Hz)

Max

Tonality

Cuts Through

vs Ambient

Golden Angle 137.5°

Maximally aperiodic · Lucas count

Energy distributed —
no pitch to lock onto

Broadband Whoosh

No clear pitch · blends with ambient · unnoticeable

Spectrum Energy distributed ↓

180

Avg Hz

Low

Tonality

Blends In

vs Ambient

The Real-World Test

Which drone do you notice above the city?

Killer Demo

Urban background noise is always present. A vehicle that passes decibel compliance but produces a tonal sound will still be noticed and opposed. Start the city ambient below, then add each drone type. You'll hear the tonal whine cut through immediately. The broadband version is harder to distinguish from the background — even at the same measured power level. This is the psychoacoustic value proposition.

Drone audibility above ambient:

—

Start city ambient first, then add a drone to hear the difference

Why character matters more than decibels

The human auditory system evolved to detect tonal signals — voices, footsteps, approaching threats — against broadband background noise. A tonal sound at a fixed frequency engages this mechanism involuntarily. You cannot stop noticing it. Equal spacing creates the worst-case profile: all acoustic energy concentrated at the blade passing frequency and its harmonics — a comb of discrete tones your ear locks onto. Golden-angle spacing produces the best-case profile: energy spread so no single frequency dominates. Psychoacoustic research quantifies the effect: tonal noise is perceived as 8–12 dB louder than broadband noise of identical measured SPL. EASA's eVTOL criteria include explicit tonal penalty factors. Same power. Different character. Different community response. Different permit outcome.

About this synthesis: Equal spacing uses a sawtooth oscillator at the blade passing frequency — mathematically equivalent to summing all harmonics. This is how acoustic engineers model a periodic blade machine. Golden angle uses shaped noise with rotational AM — broadband energy at the same frequency centroid with no periodic structure. The ambient test uses pink noise as a simplified urban background. No recordings were used; all audio is synthesized in your browser via the Web Audio API.

Same power. Same blade count.One you can't ignore. One you can.

Same power. Same blade count.
One you can't ignore. One you can.