Port Length
105.5"
Port Area
12.6 in²
Volume
56.6 L
Ported Enclosure
105.5"
Port length (267.9 cm)
Port Area
12.6 in²
Volume
56.6 L
Sealed Fb
160.2 Hz
⚠ Port air velocity may be high. Consider increasing port diameter to reduce port noise.
Inputs
Result
Vas in liters = 55 × 28.3168 = 1,557.4 L. Vb = 2.0 × 28.3168 = 56.6 L. Fb = 30 × sqrt(1557.4/56.6 + 1) = 30 × 5.34 = 160.3 Hz. Qtc = 0.40 × 5.34 = 2.14. F3 = 160.3 / 2.14 = 74.9 Hz. Note: Vas of 55 ft³ is extremely large; real 12" drivers typically have Vas of 1–3 ft³.
Inputs
Result
Port area = π × 2² = 12.57 in² = 0.00811 m². Vb = 56.6 L. L = (23562.5 × 0.00811) / (35² × 0.0566) – 0.825 × sqrt(0.00811) = 191.15 / 69.34 – 0.0743 = 2.683 m – 0.074 = 2.609 m. Port length = 2.609 m is very long; consider a larger box or higher tuning frequency.
Sealed box resonance (Fb) = Fs × sqrt(Vas/Vb + 1), where Fs is the driver free-air resonance, Vas is equivalent compliance volume, and Vb is box volume. A smaller box raises Fb, giving tighter but less deep bass.
| Qtc Value | Alignment | Sound Character | Best For |
|---|---|---|---|
| 0.50 | Over-damped | Tight, rolled off | Audiophile SQ |
| 0.577 | Bessel | Best transient | Music production |
| 0.707 | Butterworth | Flattest response | General use |
| 1.00 | Chebyshev | Peaked, punchy | Car SPL |
Port length L = (23562.5 × port area) / (Fb² × Vb) – 0.825 × sqrt(port area), where Fb is tuning frequency, Vb is net box volume in liters, and port area is in square meters. Larger ports need longer tubes.
| Port Diameter | Port Area | Best For | Noise Level |
|---|---|---|---|
| 3" | 7.1 in² | Low power (<100W) | Moderate |
| 4" | 12.6 in² | Medium (100–300W) | Low |
| 6" | 28.3 in² | High power (300W+) | Very low |
| 2×10" slot | 20 in² | Space-constrained | Low–moderate |
Thiele-Small (T/S) parameters describe a speaker driver’s mechanical and electrical properties. The three most important are Fs (free-air resonance in Hz), Qts (total Q factor), and Vas (equivalent compliance volume). They are listed on the driver spec sheet.
| Parameter | Low Value | High Value | Effect on Design |
|---|---|---|---|
| Fs | 20–25 Hz | 35–45 Hz | Lower = deeper extension |
| Qts | 0.25–0.35 | 0.45–0.60 | Lower = better for ported |
| Vas | 20–40 L | 80–200 L | Higher = larger box needed |
Sealed boxes offer tighter transient response and simpler construction but roll off at 12 dB/octave. Ported boxes extend bass 5–10 Hz lower and are 3 dB more efficient, but roll off steeply at 24 dB/octave below tuning frequency.
| Feature | Sealed | Ported |
|---|---|---|
| Bass extension | Moderate | Deeper (–5–10 Hz) |
| Efficiency | Lower | +3 dB louder |
| Transient response | Tight, accurate | Slightly slower |
| Box size | Smaller | Larger |
| Build complexity | Simple | Port must be precise |
Tuning frequency (Fb) is usually set 5–10 Hz below the driver Fs for music, or at Fs for maximum SPL. For home theater, tune 5–15 Hz below Fs to extend infrasonic bass. Lower tuning gives deeper bass but needs a larger box and longer port.
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Last Updated: Mar 25, 2026
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