Sealed vs Ported vs T-Line — Picking a Subwoofer Box

Enclosure type changes everything: the sub's frequency response, efficiency, peak SPL, distortion profile, and how it feels at the listening position. The right answer depends on the music you play, the space you have, and the SPL target. Here's a fast decision tree, followed by the trade-offs each box makes.

The 30-second decision tree

• • Want accurate, tight, music-first — and you listen to a lot of acoustic, jazz, rock, classical → SEALED
• • Want loud, peaks at tuning, daily-driver SPL, EDM/rap/hip-hop → SLOT PORT
• • Want compact + tunable + clean-sounding at SPL → AERO PORT
• • Want max output in a narrow bandwidth (one-trick pony) → BANDPASS
• • Want efficient with power, low-tuned, deep musical bass → ¼-WAVE T-LINE
• • Want the smallest enclosure footprint possible → SEALED WEDGE

Sealed — predictable and forgiving

Sealed boxes have a 12dB/octave low-end rolloff and a clean, tight response. They're smaller than ported equivalents and very tolerant of design errors — a 25% volume error in a sealed box shifts Fc by maybe 2 Hz. The trade-off is efficiency: you need roughly 2× the power for the same SPL as a ported box of the same internal volume.

Ported (slot or aero) — louder at tuning

Ported boxes use a Helmholtz resonator to reinforce a narrow band around the tuning frequency. Below tuning, output falls off fast — 24dB/octave instead of 12. The peak around Fb makes them 3–6 dB louder than sealed at that frequency. Slot ports tune low and look clean in a build; aero ports flare to reduce port noise at high SPL.

Tuning frequency is the single most important number. 33 Hz is the most common all-purpose tune. Hip-hop with deep 808s? 28–32 Hz. Rock and EDM? 33–38 Hz. SQ-leaning daily driver? 32–35 Hz with low Qtc.

Port velocity matters

A port that's too small turns into a wind tunnel at peak SPL. Air velocity above ~17 m/s starts producing audible chuff — a "whooshing" sound that overlays your bass content. Aim for under 17 m/s in SQ builds; 17–25 m/s is borderline; 25+ m/s is audible turbulence.

Bandpass — when you only need one note loud

Bandpass enclosures combine a sealed chamber and a ported chamber, with the sub firing into the ported side. The output frequency response is band-limited (hence the name), giving 3–6 dB more output across a narrow window than either sealed or ported alone. The price is everything outside that window: rolloff is steep on both sides, and tuning is unforgiving. Great for SPL competition; bad for music.