What is a 4th Order Bandpass?

A 4th‑order bandpass enclosure is a two‑chamber subwoofer box where one chamber is sealed and the other is ported, creating a design that boosts output within a controlled frequency range. This layout makes it easier to understand than a 6th‑order while still offering noticeably higher efficiency than a standard sealed box. The sealed side controls the woofer’s movement, while the ported side acts like an acoustic amplifier, shaping and projecting the bass through the port.

🔧 Core Structure

A 4th‑order bandpass has two chambers with the woofer mounted between them:

• Sealed chamber — stabilizes the woofer, tightens control, and limits cone motion.

• Ported chamber — tuned to a specific frequency to boost output.

Only the ported side produces audible sound; the sealed side is completely enclosed.

This combination is what makes it a 4th‑order system: the sealed chamber contributes two acoustic “orders,” and the ported chamber contributes two more.

🔊 How It Works

The sealed chamber keeps the woofer’s movement predictable, while the ported chamber creates a resonant peak that increases efficiency. The result is a loud, punchy band of bass centered around the port tuning. Compared to a sealed box, it plays louder in its target range; compared to a ported box, it offers more control and a smoother roll‑off.

📈 What It’s Good At

• Higher output than sealed boxes in the tuned range

• Good transient response thanks to the sealed chamber’s control

• Efficient performance for daily music listening

• Balanced compromise between loudness and sound quality

These strengths make 4th‑orders popular among everyday users and competitors looking for a blend of output and control.

⚠️ What Makes It Tricky

• Precision matters: small errors in chamber size or port tuning can hurt performance.

• Limited bandwidth: it plays best within a specific frequency window.

• Below tuning, power handling drops, so overpowering can damage the woofer.

🧠 Simple Analogy

Imagine the woofer shouting into a sealed room on one side and a tuned megaphone on the other. The sealed room keeps the woofer steady, while the megaphone shapes and boosts the sound that escapes.