6dB/Octave Butterworth Crossover Calculator

First-Order Crossover Component Values for Audio Systems

📐 Core Formulas

High-Pass Filter (Capacitor for Horn/Tweeter):
C (μF) = 159,155 / (F × R)
Where: C = Capacitance in microfarads, F = Frequency in Hz, R = Impedance in ohms

Low-Pass Filter (Inductor for Woofer):
L (mH) = (159.155 × R) / F
Where: L = Inductance in millihenries, F = Frequency in Hz, R = Impedance in ohms

High-Pass Capacitor Values for Horns/Tweeters

Crossover Frequency	8Ω Impedance	16Ω Impedance	Application
100 Hz	199 μF	99.5 μF	Large Format
200 Hz	99.5 μF	49.7 μF	Large Format
300 Hz	66.3 μF	33.2 μF	Large Format
398 Hz	50 μF	25 μF	Large Format
400 Hz	49.7 μF	24.9 μF	Large Format
500 Hz	39.8 μF	19.9 μF	Large Format
800 Hz	24.9 μF	12.4 μF	Medium Format
1000 Hz	19.9 μF	9.95 μF	Medium Format
1600 Hz	12.4 μF	6.2 μF	Medium Format
2000 Hz	9.95 μF	4.97 μF	Tweeter
3000 Hz	6.63 μF	3.32 μF	Tweeter
5000 Hz	3.98 μF	1.99 μF	Tweeter
6000 Hz	3.32 μF	1.66 μF	Tweeter

Low-Pass Inductor Values for Woofers

Crossover Frequency	8Ω Impedance	16Ω Impedance	Application
100 Hz	12.7 mH	25.5 mH	Large woofer/subwoofer
200 Hz	6.37 mH	12.7 mH	Large woofer/subwoofer
300 Hz	4.24 mH	8.49 mH	Large woofer/subwoofer
400 Hz	3.18 mH	6.37 mH	18" woofer
509 Hz	2.5 mH	5.0 mH	18" woofer
500 Hz	2.55 mH	5.09 mH	Standard woofer crossover
800 Hz	1.59 mH	3.18 mH	Mid-woofer crossover
1000 Hz	1.27 mH	2.55 mH	Small woofer/mid-bass
1600 Hz	0.796 mH	1.59 mH	Mid-bass driver
2000 Hz	0.637 mH	1.27 mH	Small mid-bass

Practical Example: System Configuration with Attenuators

Example System (6dB/octave with dual attenuators):
• 18" Woofer (8Ω): 2.5 mH inductor = plays up to ~509 Hz
• Horn (8Ω): 50 μF capacitor = starts at ~398 Hz (with attenuator for level adjustment)
• Tweeter: Capacitor value based on desired crossover point (with attenuator for level adjustment)
• Result: There's approximately 111 Hz of overlap (398-509 Hz) where both drivers are active
• Attenuators: Two L-pad or resistive attenuators allow precise level matching for midrange and tweeter

Component	Impedance	Component Value	Crossover Point
18" Woofer	8Ω	2.5 mH	509 Hz (-3dB)
Horn Driver + Attenuator	8Ω	50 μF	398 Hz (-3dB)
Tweeter (16Ω) + Attenuator	16Ω	1.99 μF	5000 Hz (-3dB)

Interactive Component Calculator

Calculate Capacitor (High-Pass)

Frequency (Hz):
Impedance (Ω):

Calculate Inductor (Low-Pass)

Frequency (Hz):
Impedance (Ω):

Important Notes:

6dB/octave (first-order) crossovers have gentle slopes, creating wide overlap regions
Phase coherence is excellent but driver integration is critical
Use air-core inductors for woofers to avoid saturation
Component tolerance of ±5% or better is recommended
Actual crossover points may vary due to driver impedance variations

* All calculations assume purely resistive loads. Real drivers have impedance variations that affect actual crossover behavior.
* The -3dB point occurs at the calculated frequency. Response continues to roll off at 6dB/octave beyond this point.