# Vented

> How a vented (bass reflex) box works in 00 Simulator: the port and its tuning, what the tuning does to F3 and port length, and its fields.

Source: https://simulator.00aud.io/docs/boxes/vented

A vented box is a closed box with a port: a tube that lets the air inside out. The air in the port bounces on the air in the box at one frequency, the tuning, and adds its output to the cone there. You get deeper bass from the same box, and a port to size.

_Figure: The vented example as the Schematic tile draws it: the Ciare 12.00SW on the baffle, its rear loading a 55 L chamber that radiates through a 10 cm port tuned to 32 Hz._

The [vented example](https://simulator.00aud.io/app?template=vented) in the [Schematic](https://simulator.00aud.io/docs/reference/tiles/schematic) tile: the Ciare 12.00SW in 55 L, tuned to 32 Hz. The cone and the port both reach the room.

The rear face loads the chamber, which radiates through a port. Cone and port both reach the room.

## How it works

The air in the port is a small mass; the air in the box is a spring. Together they resonate at the tuning frequency, Fb, the way a bottle hums when you blow across it. Around Fb the port moves most of the air and the cone barely moves; well above it the port hardly matters and the box acts much like a sealed one.

Below Fb the port and the cone work against each other and the output falls fast, close to 24 dB per octave: the example loses 22.8 dB from 20 Hz down to 10 Hz, twice the slope of a sealed box. The cone also loses the port's support there, which is the thing to watch.

## What the tuning does

The same 55 L box and 10 cm port, tuned from 28 Hz to 40 Hz. Only the port length changes.

_Figure: SPL of the 55 L vented example tuned to 28, 32, 36, 40 Hz: a lower tuning sags, a higher one humps._

Ciare 12.00SW in the 55 L vented example with its 10 cm port, at 1 W, half space, 1 m. Simulated when this page was built.

| Tuning | F3 | Port |
| --- | --- | --- |
| 28 Hz | 29.6 Hz | 48.3 cm |
| 32 Hz, the example | 30.3 Hz | 35.6 cm |
| 36 Hz | 32.6 Hz | 26.8 cm |
| 40 Hz | 35.9 Hz | 20.6 cm |

- Tune lower and the response sags into a long slope: F3 only moves from 30.3 Hz to 29.6 Hz, but the port grows from 35.6 cm to 48.3 cm.
- Tune higher and the response humps above the tuning: 3.1 dB over the level at 100 Hz at 40 Hz, against 0.5 dB for the example. F3 rises to 35.9 Hz and the port shrinks to 20.6 cm.
- A bigger box or a narrower port shortens the port for the same tuning; a wider port lengthens it. [Ports and end correction](https://simulator.00aud.io/docs/boxes/ports) has the details.

## Excursion: low at the tuning, high below it

_Figure: Cone excursion of the vented example at 200 W: lowest near the 32 Hz tuning, rising steeply below it past Xmax._

Ciare 12.00SW in the 55 L vented example at 200 W, half space, 1 m, with its 13.5 mm Xmax. Simulated when this page was built.

| Design | Least | At 20 Hz |
| --- | --- | --- |
| 32 Hz tuning at 200 W | 2.5 mm at 32.4 Hz | 12.5 mm |

At 200 W the cone moves least near the tuning, 2.5 mm at 32.4 Hz, because the port is doing the work. Below it the cone is unloaded and its travel climbs past the 13.5 mm Xmax below 18.7 Hz. If you do not need output below the tuning, a **High-pass** filter just under it keeps the cone in check.

The port has its own limit: at 200 W its air speed peaks at 28.4 m/s near 30.1 Hz, above the default 17 m/s warning line. This flags a risk of noise; the actual onset depends on the port’s shape and ends. The [Port Velocity](https://simulator.00aud.io/docs/reference/tiles/port-velocity) tile shows it, and [Fix a noisy port](https://simulator.00aud.io/docs/guides/noisy-port) shows what to change.

## What you set

Choose **Vented** in **Type** at the top of the enclosure panel. The vented fields are:

| Field | What it sets |
| --- | --- |
| **Volume** | The net internal volume: the air in the box, not counting the ports, the driver or bracing. |
| **Tuning** | The box’s tuning frequency, Fb, from 15 to 1,200 Hz. |
| **Port length** | The physical length of each port for that tuning. Tuning and port length are a pair: set one and the other follows. The one you set last is held when you change the port’s size: with the tuning held, a wider port gets longer; with the length held, the tuning moves instead. A warning beside it means the port is too narrow for the tuning: make it wider or add ports. |
| **Port › Shape** | A round port, a slot, or a custom **Cross-sectional area**. |
| **Number of ports** | From 1 to 10 identical ports, each as long as **Port length**. |
| **Diameter**, or **Width** and **Height** | The size of each port: a diameter for a round port, width and height for a slot. |
| **Advanced** | **End correction** and **Port model**, under **Port**. See [Ports and end correction](https://simulator.00aud.io/docs/boxes/ports). |
| **Results** | **Cross-sectional area** (all ports together), **Port volume**, **Gross volume** (net volume plus ports and anything under **Box volume adjustments**) and **1st port resonance**. |

> **Check the port fits** The example’s port is 35.6 cm long inside a 55 L box. **1st port resonance** under **Results** is the pipe resonance of that length (482 Hz here); a long port puts it lower, closer to the band you use.

## When to use it

### Good for

- Deeper bass from the same box. With the same Dayton Audio DCS165-4 in 10 L, the vented box reaches F3 35.9 Hz and the sealed one 77.5 Hz ([one driver, four boxes](https://simulator.00aud.io/docs/boxes#one-driver-four-boxes)).
- Little cone travel around the tuning, where the port does the work: more level for the same excursion.
- Drivers with a high EBP (Fs divided by Qes). When you add an enclosure, 00 Simulator suggests **Vented** for an EBP above 75; the Ciare 12.00SW’s is 88.

### Watch for

- The cone below the tuning, where it has no support: use a **High-pass** filter and read the [Excursion](https://simulator.00aud.io/docs/reference/tiles/excursion) tile at full power.
- Port noise: keep the air speed under the 17 m/s line at the power you plan to use, or make the port bigger.
- Port length: a low tuning or a wide port makes a long port. In a small box it may not fit; the [comparison](https://simulator.00aud.io/docs/boxes#one-driver-four-boxes) needs a 43.7 cm port in 10 L, where a [passive radiator](https://simulator.00aud.io/docs/boxes/passive-radiator) is the usual answer.

## Try it

_Interactive walkthrough in the page: the simulator's own tiles running a short demo._

The vented example at 100 W in the app’s own tiles, as the tuning drops to 28 Hz and a second port goes in.

To keep going, [open the vented example](https://simulator.00aud.io/app?template=vented) in the simulator: the Ciare 12.00SW in 55 L tuned to 32 Hz, as on this page. [Open it at 200 W](https://simulator.00aud.io/app?template=vented&power=200) to see the limits.

## Tiles to watch

- [SPL (dB)](https://simulator.00aud.io/docs/reference/tiles/spl): The tuning, the roll-off below it and F3.
- [Excursion](https://simulator.00aud.io/docs/reference/tiles/excursion): The dip at the tuning and the climb below it.
- [Port Velocity](https://simulator.00aud.io/docs/reference/tiles/port-velocity): Air speed in the port against the 17 m/s line.
- [Impedance](https://simulator.00aud.io/docs/reference/tiles/impedance): Two peaks, at 19.1 Hz and 49.9 Hz in the example, with a dip near the tuning between them (31.6 Hz).
- [Max SPL (dB)](https://simulator.00aud.io/docs/reference/tiles/max-spl): How loud it can play before excursion, heat or the port stop it.

## Ask your AI

**Ask your AI**

Your assistant tries the changes with the same solver, through the 00 Simulator connector, and saves nothing unless you ask.

> Using 00 Simulator, for the vented box in my open workspace, try the tuning 4 Hz lower and 4 Hz higher without saving. Tell me each option’s F3, port length and peak port air speed at its set power, and which one you would build.