First-Order Speaker Crossover Calculator (6 dB/octave)
Use this tool to calculate capacitor and inductor values for a simple first-order loudspeaker crossover network.
Tip: This calculator assumes ideal components and a purely resistive load equal to the nominal speaker impedance.
What is a first-order crossover?
A first-order crossover is the simplest passive filter used in speaker design. It uses one reactive component per filter section:
- High-pass filter: one series capacitor (typically for a tweeter)
- Low-pass filter: one series inductor (typically for a woofer)
First-order networks have a slope of 6 dB per octave. They are easy to build, inexpensive, and can sound very natural when drivers are well matched.
Core formulas used by the calculator
High-pass capacitor (series):C = 1 / (2π f Z)
Low-pass inductor (series):L = Z / (2π f)
Where: f = crossover frequency (Hz), Z = nominal impedance (Ω), C in farads, L in henries.
How to use this calculator
Step 1: Enter your target crossover frequency
Choose a frequency that fits both drivers. For example, many 2-way designs cross between 1.8 kHz and 3.5 kHz, depending on tweeter limits and woofer breakup behavior.
Step 2: Enter nominal impedance
Typical values are 4 Ω, 6 Ω, or 8 Ω. Use the rated nominal impedance of the individual driver for the section you are calculating.
Step 3: Select low-pass, high-pass, or both
The calculator returns practical units:
- Capacitor values in µF and nF
- Inductor values in mH and µH
Worked example
Suppose you want a first-order crossover at 2500 Hz with 8 Ω drivers:
- High-pass capacitor: approximately 7.96 µF
- Low-pass inductor: approximately 0.509 mH
In practice, you would choose the closest standard component values (for example, 8.2 µF and 0.5 mH) and then measure/tune.
Quick reference values
| Impedance | Crossover Frequency | Capacitor (High-pass) | Inductor (Low-pass) |
|---|---|---|---|
| 4 Ω | 2000 Hz | 19.89 µF | 0.318 mH |
| 8 Ω | 2000 Hz | 9.95 µF | 0.637 mH |
| 4 Ω | 3000 Hz | 13.26 µF | 0.212 mH |
| 8 Ω | 3000 Hz | 6.63 µF | 0.424 mH |
Real-world design notes
1) Speaker impedance is not constant
The impedance of real drivers changes with frequency. A “8 Ω” driver may be much higher around resonance and vary across the passband. That means actual acoustic crossover behavior will differ from ideal math.
2) Component tolerances matter
Capacitors and inductors come with tolerances (e.g., ±5%, ±10%). For tighter matching between channels, use components with lower tolerance and measure if possible.
3) Physical driver behavior matters more than textbook values
A passive crossover design is not just electrical. Driver frequency response, phase, sensitivity, and placement all affect the final result. Use this calculator as a starting point, then validate with measurements.
When should you choose first-order?
- You want a simple, low-part-count design.
- Your drivers overlap smoothly and have good off-axis behavior.
- You are comfortable with gentler attenuation and wider overlap.
If you need steeper roll-off, better power handling at band edges, or stricter driver protection, consider second-order or higher crossovers.