Guides · Design
Fix a noisy port
Check the port#
- 1
Open the example at 200 W
Open the vented example at 200 W: 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).
Port Velocity
m/s
- One 100 mm port28.4 m/s at 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.
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.)
Port Velocity
m/s
- One 100 mm port, 200 W28.4 m/s at 30 Hz
- Two 100 mm ports14.2 m/s at 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.
Port Velocity
m/s
- One 100 mm port, 200 W28.4 m/s at 30 Hz
- One 130 mm port16.8 m/s at 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.
Port Velocity
m/s
- One 100 mm port, 200 W28.4 m/s at 30 Hz
- One 100 mm port, 71 W16.9 m/s at 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.
Port Velocity
m/s
- One 100 mm port, 200 W28.4 m/s at 30 Hz
- 35 Hz high-pass16.4 m/s at 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.
Compare the fixes#
| 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 | 14.2 m/s | Each 771 mm long, 12.1 L; gross volume 67.1 L |
| One 130 mm port | 16.8 m/s | 624 mm long, 8.3 L; gross volume 63.3 L |
| 71 W instead of 200 W | 16.9 m/s | 4.5 dB quieter everywhere |
| 35 Hz high-pass | 16.4 m/s | F3 up to 36.8 Hz, 5.1 dB less at the tuning |
Port length
mm
Inside edge of a 55 L cube: 380 mm
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).
Ask your AI#
Ask your AI
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.
Connect your assistant so it can open your designs.