# Port Velocity (Rear Chamber)

> Check the rear port of a sixth-order bandpass separately from its front port, using the same air-speed warning and power setting.

Source: https://simulator.00aud.io/docs/reference/tiles/rear-port-velocity

A sixth-order bandpass can have a quiet front port and a noisy rear one. This tile reads the rear chamber’s port independently.

- **Shows:** Peak air speed in a bandpass box’s rear-chamber port, in m/s, at each frequency, against the warning line.
- **Healthy when:** The curve stays under the line at the power you will actually use.
- **If it is not:** More rear port area, less power, or a high-pass below the band you play.

## The tile

_Figure: Rear port air speed with one and two rear ports at the same tuning._

Sixth-order bandpass bench design at 100 W, half space, 1 m. Simulated when this page was built.

| Port Velocity (Rear Chamber) | Peak | At |
| --- | --- | --- |
| One rear port | 19.8 m/s | 20 Hz |
| Two rear ports | 9.9 m/s | 20 Hz |

The rear port peaks at 19.8 m/s near 19.6 Hz. With two rear ports it peaks at 9.9 m/s. Both use the same rear-chamber volume and target tuning.

Use **Port Velocity** for the front chamber and this tile for the rear. A sealed rear chamber has no rear-port curve. A rear chamber loaded by a passive radiator belongs on **PR Excursion** instead.

## Read the warning at your working power

The dashed line is the same adjustable port-speed warning used by the front-port tile, 17 m/s in this example. It is a warning threshold, not a prediction of exactly when a particular port will become audible.

| Change on the rear chamber | Trade-off |
| --- | --- |
| More port area | Lower air speed at the same tuning, with longer ports. |
| Lower tuning | Moves the low-frequency behaviour and increases required port length. |
| Less input power | Reduces both front and rear port speeds, along with output. |
| A high-pass below the band | Removes demand where little useful sound remains; recheck the lower passband edge. |

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

The live bench shows how both chambers affect the result.

## What to try

| Try | What it changes |
| --- | --- |
| [More rear port area](https://simulator.00aud.io/docs/boxes/bandpass-6) | On the **Rear** tab, a second port or a wider one slows the air for the same tuning. Each port gets longer. |
| [A high-pass below the band](https://simulator.00aud.io/docs/guides/eq-and-filters) | If the peak sits below the band you play, a high-pass there slows the air for little output. |
| Less power | Air speed follows the square root of power: half the power is about 0.7 times the speed, and 3 dB quieter. |

## Ask your AI

**Ask your AI**

> Using 00 Simulator, check both port velocities in my sixth-order bandpass at its current power. Preview more area on whichever port exceeds the warning, keeping the chamber tunings fixed, and report the new speeds and port lengths.