Calculator Inputs
Enter driver, enclosure, and port values. Results appear above this form after submission.
Formula Used
Free-air resonance:
Fs = 1 / (2π × √(Mms × Cms))
Mechanical stiffness:
Kms = 1 / Cms
Total Q:
Qts = (Qms × Qes) / (Qms + Qes)
Sealed box resonance:
Fc = Fs × √(1 + Vas / Vb)
Sealed box damping:
Qtc = Qts × √(1 + Vas / Vb)
Port tuning:
Fb = c / (2π) × √(S / (Vb × Leff))
Mass is converted from grams to kilograms. Compliance is converted from mm/N to m/N. Box volume is converted from liters to cubic meters.
How to Use This Calculator
- Enter the speaker moving mass from the data sheet.
- Add air load mass when it is listed separately.
- Select compliance mode or stiffness mode.
- Enter Qms, Qes, Re, Vas, and box volume.
- Add port diameter and length for vented box tuning.
- Press the calculate button.
- Review Fs, Fc, Fb, Qtc, and impedance results.
- Use CSV or PDF buttons to save the results.
Example Data Table
| Driver Type | Mms | Cms | Qms | Qes | Vas | Box | Expected Use |
|---|---|---|---|---|---|---|---|
| Small Midrange | 9 g | 0.45 mm/N | 3.2 | 0.65 | 7 L | 3 L sealed | Voice and instruments |
| Hi-Fi Woofer | 35 g | 0.85 mm/N | 4.8 | 0.42 | 58 L | 32 L vented | Deep bass design |
| Subwoofer | 135 g | 0.28 mm/N | 6.1 | 0.39 | 82 L | 55 L vented | Low frequency output |
Speaker Resonance Guide
What Resonance Means
A speaker driver is a mass spring system. The cone, coil, dust cap, and trapped air form the moving mass. The surround and spider form the spring. When these parts trade energy, the driver reaches its natural resonance. This point is called Fs in free air.
Why Fs Matters
Resonant frequency matters because output rises and falls around it. Below resonance, cone control becomes weak. Excursion can climb fast. Above resonance, the driver behaves more predictably. A woofer with a low Fs can support deeper bass. A midrange with a higher Fs can still work well when crossed over safely.
Input Values
This calculator uses moving mass and compliance to estimate free air resonance. It can also use stiffness when compliance is not known. These values are common in driver data sheets. Mass is entered in grams. Compliance is entered in millimeters per newton. The tool converts units before solving the formula.
Sealed Box Behavior
The page also estimates sealed box behavior. A sealed enclosure adds air stiffness. That usually raises the system resonance. It also changes Qtc. A Qtc near 0.707 is often called a balanced alignment. Lower values sound tighter but may lose depth. Higher values can add warmth, but may peak near resonance.
Vented Box Tuning
For vented designs, the port calculator estimates Helmholtz tuning. It uses box volume, port area, effective port length, and sound speed. Temperature is included because sound speed changes with air conditions. The result helps compare driver resonance with enclosure tuning.
Impedance Guidance
Use the impedance estimate as a guide, not a lab result. Real impedance depends on motor design, inductance, losses, leakage, and cabinet damping. Still, the peak estimate helps explain why resonance can affect amplifier loading.
Design Check
The graph shows a simple resonance peak. It is useful for visual checking. Compare free air Fs, sealed Fc, and port Fb. Keep the final design within the driver limits. Test with real measurements before building a costly cabinet.
Better Input Data
Good input data improves every estimate. Use measured Thiele Small values when possible. Enter the total moving mass, not only cone mass. Add known air load if your data sheet separates it. Match units carefully. Small unit mistakes can create very large frequency errors during early design checks.
FAQs
1. What is speaker resonant frequency?
It is the natural frequency where the speaker moving mass and suspension compliance store and release energy most easily. It is often called Fs in driver data sheets.
2. What units should I use?
Use grams for moving mass, millimeters per newton for compliance, liters for volume, centimeters for port dimensions, and ohms for voice coil resistance.
3. Can I use stiffness instead of compliance?
Yes. Select stiffness mode and enter Kms in newtons per meter. The calculator converts stiffness into compliance before solving resonance.
4. Why does a sealed box raise resonance?
The trapped air inside the sealed box acts like an added spring. This makes the suspension system stiffer and raises the system resonance.
5. What is Qtc?
Qtc is the total damping of the driver inside a sealed enclosure. It helps describe bass shape, tightness, peaking, and rolloff behavior.
6. Is the impedance peak exact?
No. It is an estimate. Real impedance depends on motor design, inductance, losses, enclosure leakage, damping material, and measurement conditions.
7. What is port tuning Fb?
Fb is the estimated tuning frequency of a vented enclosure. It depends on box volume, port area, effective port length, and sound speed.
8. Should I rely only on this calculator?
No. Use it for planning and comparison. Always verify the final speaker design with real measurements and safe power testing.