Boxes

Boxes · Box type

BOX TYPEONE CHAMBER

Sealed

A sealed box is the driver in a closed, airtight box. The air trapped behind the cone is a spring, so the size of the box decides where the bass rolls off and how sharply. It is the simplest box to design and build, and the one to compare every other type with.
Chamber
15 L
Cone
Baffle
DCS205-4
1 W·3.9 Ω
The sealed example in the Schematic tile: the Dayton Audio DCS205-4 in 15 L. Only the cone reaches the room.

How it works#

When the cone moves in, it squeezes the air in the box; when it moves out, it stretches it. That air pushes back like a spring, added to the driver's own suspension, so the driver resonates higher in the box than it does on its own. The Dayton Audio DCS205-4 resonates at 32.3 Hz in free air and at 54 Hz in the example's 15 L.

Two numbers describe the result, and the enclosure panel shows both: Fsc, the box's resonance (the system resonance), and Qtc, how sharply the response turns at it (the system Q). The example's Qtc is 0.62, and its F3 is 62.2 Hz.

Below the resonance the output falls at close to 12 dB per octave: the example loses 12.0 dB from 20 Hz down to 10 Hz. That is half the slope of a vented box, and it is the whole of the low end: only the cone radiates, so there is no port to tune or to hear.

What the volume does#

The same Dayton Audio DCS205-4 in four sealed boxes, from 6 L to 40 L:

SPL

dB

  • 6 LQtc 0.87 · F3 69.5 Hz
  • 10.2 L, suggestedQtc 0.71 · F3 63 Hz
  • 15 L, the exampleQtc 0.62 · F3 62.2 Hz
  • 40 LQtc 0.48 · F3 64.9 Hz
Dayton Audio DCS205-4 at 1 W, half space, 1 m. Simulated when this page was built.
  • A smaller box is a stiffer spring. In 6 L the resonance rises to 75.8 Hz and Qtc to 0.87, so the knee is higher and sharper.
  • A bigger box is a softer spring. In 40 L Qtc falls to 0.48 and the curve starts to droop earlier, so F3 barely moves: 63 Hz in 10.2 L, 64.9 Hz in 40 L.
  • What a bigger box does buy is the very bottom: at 20 Hz the 40 L box is 8.6 dB louder than the 6 L one.

Excursion: a smaller box holds the cone#

In a sealed box the cone does all the work, and its travel keeps rising as the frequency falls until it levels off below the resonance. The box's air spring is what holds it back, so the bigger, softer box lets it travel further.

Excursion

mm

  • 6 LAt 20 Hz 4.0 mm
  • 10.2 L, suggestedAt 20 Hz 5.7 mm
  • 15 L, the exampleAt 20 Hz 7.0 mm
  • 40 LAt 20 Hz 10.0 mm
Dayton Audio DCS205-4 at 50 W, half space, 1 m, with its 8.8 mm Xmax. Simulated when this page was built.

At 50 W and 20 Hz the cone moves 7.0 mm in the example, inside its 8.8 mm Xmax, and 10.0 mm in 40 L, past it. A sealed box runs out of travel at its lowest notes first, so read the Excursion tile at the power you plan to use, and add a High-pass filter below the band you need if it crosses the line.

What you set#

Choose Sealed in Type at the top of the enclosure panel. The sealed fields are:

FieldWhat it sets
VolumeThe net internal volume: the air behind the cone, not counting the driver, bracing or anything else inside. Type a value from 0.01 L up, or drag the slider under it (1 to 1,000 L). Click the unit to change it.
Fsc, system resonanceThe box’s resonance with the chosen driver. Type a frequency and the volume changes to give it. It cannot go below the driver’s Fs.
Qtc, system QHow sharply the response turns at that resonance. Type a Q and the volume changes to give it. It cannot go below the driver’s Qts.
Results › Gross volumeShown once you add volume under Box volume adjustments: the net volume plus what sits inside, which is the box to build.
Box volume adjustmentsDriver displacement and Bracing / other: volume taken up inside the box.

Fsc and Qtc appear once the enclosure has a driver, and count every driver in it: two drivers in the same volume behave like one driver with twice the Vas. Baffle step sits below, as it does for every type; see Controls and fields.

When to use it#

Good for#

  • Simple builds: one closed box, nothing to tune and no port to fit or to hear.
  • A gentle roll-off that EQ can reshape: the Linkwitz transform filter retunes a sealed box’s response.
  • Tight timing. With the same Dayton Audio DCS165-4 in the same 10 L, the sealed box delays 40 Hz by 4.0 ms and the vented box by 13.6 ms (the Group Delay tile).

Watch for#

  • Less deep bass than a vented box of the same size: in that 10 L comparison the sealed box is 6.9 dB quieter at 35 Hz (one driver, four boxes).
  • Excursion at the bottom. The cone does all the work and travels furthest at the lowest notes, so that is where it meets Xmax first.
  • A bigger box is not a lower F3 with a low-Qts driver like the Dayton Audio DCS205-4 (Qts 0.37): Qtc falls and the response droops sooner instead.

Try it#

Start from the sealed exampleA 15 L sealed box at 50 W. The grey line is an unchanged copy. From 20 Hz up, the cone stays inside the dashed Xmax line.
Schematic
Simulating…
SPL (dB)
Simulating…
Excursion
Simulating…

The sealed example at 50 W in the app’s own tiles, as the box grows to 30 L and shrinks to 8 L.

To keep going, open the sealed example in the simulator: the Dayton Audio DCS205-4 in 15 L, as on this page. Change Volume or type a system Q and watch the curves follow, or open it at 50 W to read the excursion.

Tiles to watch#

SPL (dB)Where the box rolls off, and its F3.ExcursionHow far the cone travels against Xmax, most at the bottom.ImpedanceOne peak, at the box’s resonance: 53.6 Hz in the example.Max SPL (dB)How loud it can play before excursion or heat stop it.Group DelayThe timing a sealed box is known for.

Ask your AI#

Ask your AI

Your assistant sizes and simulates the box with the same solver, through the 00 Simulator connector.
Using 00 Simulator, add a sealed box to my open workspace with the same driver as my first enclosure, sized for a Qtc of 0.707. Simulate it at the same power and tell me its F3 and the frequency below which the cone passes Xmax.
or open it inClaudeChatGPT

Connect your assistant so it can open your designs.

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