# Fix a noisy port

> Bring a vented box’s port under the air speed warning in 00 Simulator: more port area, less power or a high-pass, and what each fix costs.

Source: https://simulator.00aud.io/docs/guides/noisy-port

A port chuffs when the air in it moves too fast. This guide takes the vented example from over the 17 m/s line to under it four ways, and shows what each fix costs: a longer port, less level or less bass.

## Check the port

1. **Open the example at 200 W.** [Open the vented example at 200 W](https://simulator.00aud.io/app?template=vented&power=200): the Ciare 12.00SW in 55 L, tuned to 32 Hz through one 100 mm port. It opens with the **Port Velocity** tile; in your own design, add it with **Add tile**.
2. **Read the peak against the line.** The curve is the air speed in the port at each frequency. The dashed line is the warning, 17 m/s unless you have changed it. Hover the curve to read the speed at a frequency.
3. **Read it at the power you will use.** Air speed follows the drive level. A port that is quiet at 10 W can chuff at 200 W, so set **Input power** first ([Power and limits](https://simulator.00aud.io/docs/guides/power-and-limits)).

_Figure: The Port Velocity tile for the vented example at 200 W: the air in its one 100 mm port peaks at 28.4 m/s near 30 Hz, over the 17 m/s 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 100 mm port | 28.4 m/s | 30 Hz |

The air peaks at **28.4 m/s** near 30 Hz, a little below the 32 Hz tuning, where the port does most of the work. To bring it under 17 m/s you can give the air more room, send less power, or stop feeding the port the frequencies that drive it hardest.

> **Is the line right for your port?** Set it with **Port velocity** under **Settings › Simulation…**, from 10 to 30 m/s. The app’s hint says 15 to 20 m/s is typical, higher for flared ports. Change the line only for a port you will really build that way; it does not change the air speed.

## More port area

The same air through a bigger opening moves more slowly. The catch is length: to keep the same tuning, a port with more area has to be longer.

### Add a second port

1. **Open the port settings.** Select the enclosure. In the **Enclosure** panel, open **Port**.
2. **Set two ports.** Set **Number of ports** to 2. **Tuning** stays at 32 Hz, so the SPL curve does not move, and **Port length** grows to keep it. (If you last typed a **Port length**, the panel holds that instead and the tuning moves; type the tuning again to get it back.)

_Figure: Port Velocity with two 100 mm ports: the peak falls from 28.4 m/s to 14.2 m/s, under the 17 m/s 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 100 mm port, 200 W | 28.4 m/s | 30 Hz |
| Two 100 mm ports | 14.2 m/s | 30 Hz |

Twice the area halves the speed: **14.2 m/s**. Each port is now 771 mm long instead of 356 mm, and the two take up 12.1 L of the box instead of 2.8 L. **Results**, under the port, shows it as **Port volume**, and **Gross volume** becomes 67.1 L: the box you build gets bigger, because the 55 L you set is the air around the ports.

### Use a wider port

1. **Widen the port.** In **Port**, raise **Diameter**. For this box, 130 mm is the smallest round port, in whole centimetres, that gets under the line.
2. **Check the length.** **Port length** follows: 624 mm.

_Figure: Port Velocity with one 130 mm port: the peak falls from 28.4 m/s to 16.8 m/s, just under the 17 m/s 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 100 mm port, 200 W | 28.4 m/s | 30 Hz |
| One 130 mm port | 16.8 m/s | 30 Hz |

The peak falls to **16.8 m/s**, with less margin than two ports but a shorter port: 624 mm long, taking 8.3 L. For the model’s average air speed, total area is what counts: a slot port with the same area as the 100 mm round one peaks at the same 28.4 m/s. Shape, aspect ratio and the port ends still affect noise in a real port.

## Send less power

1. **Open Power.** In the Driver panel, open **Power**.
2. **Lower the input power.** Set **Input power** to 71 W. Air speed follows the square root of power, so the peak falls by the square root of the ratio.

_Figure: Port Velocity at 71 W instead of 200 W: the peak falls from 28.4 m/s to 16.9 m/s._

The same box at 71 W and 200 W, half space, 1 m. Simulated when this page was built.

| Port Velocity | Peak | At |
| --- | --- | --- |
| One 100 mm port, 200 W | 28.4 m/s | 30 Hz |
| One 100 mm port, 71 W | 16.9 m/s | 30 Hz |

71 W is the most this port takes and stays under the line: **16.9 m/s**. Nothing in the box changes, but everything is 4.5 dB quieter at every frequency. If the level matters more than the box size, a fix with more port area is the better trade.

## Add a high-pass

1. **Add the filter.** In the Driver panel, open **EQ / filters** and choose **Add** › **High-pass filter**. A new high-pass is Butterworth, 24 dB per octave.
2. **Set the cutoff.** Set **Cutoff** to 35 Hz, the lowest whole-hertz cutoff that brings this port under the line.

_Figure: Port Velocity with a 35 Hz high-pass: the peak falls from 28.4 m/s to 16.4 m/s._

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 100 mm port, 200 W | 28.4 m/s | 30 Hz |
| 35 Hz high-pass | 16.4 m/s | 34 Hz |

The port peaks at **16.4 m/s**, but the filter has to sit above the 32 Hz tuning to do it, and that costs bass: F3 rises from 30.3 Hz to 36.8 Hz, and the level at the tuning drops 5.1 dB. A gentler 25 Hz high-pass moves F3 only to 31.1 Hz, and leaves the port at 26.0 m/s.

> **A high-pass is still worth having** Below the tuning the port stops holding the cone back, and a high-pass there keeps the cone inside Xmax. It just does not fix the port, which works hardest at the tuning itself. [Limits: travel, heat and air](https://simulator.00aud.io/docs/start/limits) shows a high-pass on the **Excursion** tile.

## Compare the fixes

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.

| Fix | Peak air speed | What it costs |
| --- | --- | --- |
| None: one 100 mm port at 200 W | 28.4 m/s | Port 356 mm long, 2.8 L |
| [Two 100 mm ports](#add-a-second-port) | 14.2 m/s | Each 771 mm long, 12.1 L; gross volume 67.1 L |
| [One 130 mm port](#use-a-wider-port) | 16.8 m/s | 624 mm long, 8.3 L; gross volume 63.3 L |
| [71 W instead of 200 W](#less-power) | 16.9 m/s | 4.5 dB quieter everywhere |
| [35 Hz high-pass](#high-pass) | 16.4 m/s | F3 up to 36.8 Hz, 5.1 dB less at the tuning |

_Figure: Port length for each fix: one 100 mm port 356 mm, two ports 771 mm each, one 130 mm port 624 mm, against the 380 mm inside edge of a 55 L cube._

| Port | Length | Port volume | Gross volume |
| --- | --- | --- | --- |
| One 100 mm port | 356 mm | 2.8 L | 57.8 L |
| Two 100 mm ports | 771 mm each | 12.1 L | 67.1 L |
| One 130 mm port | 624 mm | 8.3 L | 63.3 L |

For scale, a 55 L cube is 380 mm along each inside edge.

Both port fixes need a port longer than the inside of a 55 L cube, so neither fits straight in a box that shape. Longer ports also resonate lower: the **1st port resonance** under **Results** falls from 482 Hz with one port to 222 Hz with two. Keep it well above the band the box plays.

- Fixes add up. A 120 mm port at 145 W peaks at 16.8 m/s, with a 526 mm port and 1.4 dB less level.
- Lowering the tuning is not a fix. At 28 Hz the peak only drops to 26.4 m/s and moves down with the tuning, while the port grows to 483 mm.
- Try each one without losing the original: duplicate the enclosure first and compare the two on the same tiles ([Compare designs](https://simulator.00aud.io/docs/guides/compare)).

## Ask your AI

**Ask your AI**

Your assistant runs the same solver on your own designs through the 00 Simulator connector, and can try each fix without changing your workspace.

> Using 00 Simulator, check the port air speed of every vented enclosure in my open workspace at its set power. Where it passes 17 m/s, try a second port, a wider port and a high-pass below the tuning without saving, and tell me each option's peak air speed, port length and what it costs in level or bass.