# Port Velocity

> How to read the Port Velocity tile in 00 Simulator: peak air speed in a vented box’s port against the warning line, and what to change when it chuffs.

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

How fast air moves through the port, at its peak, at each frequency. High air speed increases the risk of chuffing and whistles, so this is the tile to size a port with.

- **Shows:** Peak air speed in the 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 port area, less power, or a high-pass below the tuning.

## The tile

_Figure: The Port Velocity tile for the vented example at 200 W, with the 17 m/s warning line._

Ciare 12.00SW in the 55 L vented example tuned to 32 Hz, at 200 W, half space, 1 m. Simulated when this page was built.

| Port Velocity | Peak | At |
| --- | --- | --- |
| One 10 cm port | 28.4 m/s | 30 Hz |

In this example the port peaks at 28.4 m/s near 30 Hz, over the 17 m/s line. Each visible enclosure with a port draws its own curve in its colour; the dashed line is the port velocity warning, and the same value shows in the tile's header.

- [Open this example](https://simulator.00aud.io/app?template=vented&power=200) in the simulator at 200 W, then hover the curve for the speed at a frequency.
- Click the warning value in the tile header to change the line. It is the same setting as **Port velocity** under **Settings › Simulation…**, from 10 to 30 m/s.
- Bandpass boxes show their front port here. A sixth-order bandpass has a second, rear-chamber port on its own tile, [Port Velocity (Rear Chamber)](https://simulator.00aud.io/docs/reference/tiles/rear-port-velocity).

## How to read it

- Read it at the power you plan to use. Air speed follows the drive, so a port that is fine at 10 W can chuff at 200 W.
- The peak sits near the box tuning, where the port does most of the work and the cone the least.
- Inspect speeds throughout the band your signal reaches. The line is a warning threshold, not a promise that a real port is quiet below it.
- 17 m/s is the default warning, not a universal noise threshold. A well-flared port can run faster before you hear it; the settings hint says 15 to 20 m/s is typical and higher for flared ports.

## Three port-area choices

The same 55 L box and driver at 200 W, with three ports that all keep the 32 Hz tuning.

_Figure: Three ports on the same box at 200 W: two 10 cm ports, one 10 cm port and one 7.5 cm port._

| Case | Peak | At | Note |
| --- | --- | --- | --- |
| Two 10 cm ports | 14.2 m/s | 30 Hz | 14.2 m/s · each 77.1 cm long |
| One 10 cm port | 28.4 m/s | 30 Hz | 28.4 m/s · 35.6 cm long |
| One 7.5 cm port | 50.5 m/s | 30 Hz | 50.5 m/s · 18.9 cm long |

Ciare 12.00SW in the 55 L vented example tuned to 32 Hz, at 200 W, half space, 1 m. Simulated when this page was built.

> **Quieter ports are longer ports** Halving the air speed took twice the port area, and to keep the same tuning each port grew from 35.6 cm to 77.1 cm. Check it fits the box before you build: the port length shows in the enclosure panel.

## What moves it

| Change | Effect | Why |
| --- | --- | --- |
| Halve the power | × 0.71 | Air speed grows with the square root of power. |
| Double the port area | × 0.50 | Same air, twice the opening. The port gets longer to keep the tuning. |
| Lower the tuning | Peak moves down | And the port gets longer for the same area. |
| High-pass below the tuning | Lower peak | The cone moves less air near the tuning. |

## What to try

| Try | What it changes |
| --- | --- |
| [More port area](https://simulator.00aud.io/docs/guides/noisy-port) | A second port, or a wider one, halves the speed for twice the area. Each port gets longer to keep the tuning. |
| Less power | Air speed follows the square root of power: half the power is about 0.7 times the speed, and 3 dB quieter. |
| [A high-pass below the tuning](https://simulator.00aud.io/docs/guides/eq-and-filters) | The cone moves less air near the tuning, so the port does too. |

## Ask your AI

**Ask your AI**

Your assistant runs the same solver on your own designs through the 00 Simulator connector.

> Using 00 Simulator, check every vented box in my open workspace at its set power. For any port above 17 m/s, try two ports and a larger diameter without saving, and tell me each option’s peak air speed and port length.