Boxes · Box type
BOX TYPEONE CHAMBERPASSIVE RADIATORPassive radiator
How it works#
The radiator sits in the baffle where a port would go. When the cone pushes the air in the box, the air pushes the radiator. Its moving mass on the box’s air spring resonates like the air in a port, and that resonance is the box’s tuning: Box tuning (Fb) under Results, 36 Hz in the example.
Unlike the air in a port, a radiator has a suspension of its own, so it also has its own resonance. Below the tuning the output falls into a notch near that resonance, where the radiator and the cone cancel. That, and the radiator’s own travel, are what a port does not have.
Tune it with added mass#
Adding mass to the radiator is how you tune the box. The example with 25, 50, 100 g added:
SPL
dB
- No added mass, the exampleFb 36 Hz · At 30 Hz 65.7 dB
- 25 g addedFb 31.2 Hz · At 30 Hz 71.3 dB
- 50 g addedFb 28 Hz · At 30 Hz 73.6 dB
- 100 g addedFb 23.7 Hz · At 30 Hz 73.3 dB
Each gram lowers the tuning: 50 g takes it from 36 Hz to 28 Hz, and makes the box 7.9 dB louder at 30 Hz. The price is a little of the upper bass: 0.6 dB at 60 Hz.
| Change from the example | Box tuning (Fb) |
|---|---|
| None | 36 Hz |
| 50 g of Added mass (tuning) | 28 Hz |
| Two radiators (Number of PRs 2) | 41.4 Hz |
| Twice the volume, 20 L | 32.9 Hz |
A second radiator doubles the moving area and raises the tuning, like a second port; add mass to bring it back down. A bigger box is a softer spring and lowers it.
Choose a radiator that suits the box#
Two radiators can give a box the same tuning and very different bass. Here the example’s Dayton Audio DCS165-4 and 10 L are tuned to about 35.4 Hz by a port, by a soft radiator with mass added, and by the example’s own radiator:
SPL
dB
- 5 cm portFb 35.4 Hz · F3 35.9 Hz
- SB Acoustics SB15SFCR-00, 50 g addedFb 35.4 Hz · F3 35.6 Hz
- Dayton Audio E150HE-PR, the exampleFb 36 Hz · F3 63.8 Hz
- The SB Acoustics SB15SFCR-00 resonates at 21 Hz on its own (the Fs the radiator list shows beside its name), and its suspension is soft: its Vas is 41.8 L, far more than the box. With mass added it follows the port down to F3 35.6 Hz, then drops into its notch: 26.4 dB below the port at 15.4 Hz.
- The Dayton Audio E150HE-PR resonates at 30 Hz, close to the tuning, and its Vas is 4.8 L, stiffer than the 10 L of air behind it. At the same tuning its F3 is 63.8 Hz.
- The port matches the soft radiator, but it has to be 43.7 cm long, about twice the inside of a 10 L cube (21.5 cm a side).
Two things move: the cone and the radiator#
The radiator moves most around the tuning, where it does the work, and has its own Xmax. The PR Excursion tile draws its travel with a dashed PR Xmax line; read it beside the cone’s Excursion tile. The example at 20 W:
Cone, Dayton Audio DCS165-4
OVERExcursion
mm
8.1 mm at 10 Hz · Xmax 6.0 mm
Radiator, Dayton Audio E150HE-PR
UNDERPR Excursion
mm
6.0 mm at 33.2 Hz · PR Xmax 19.0 mm
Below the tuning the radiator stops holding the cone back, as a port does, and the cone passes its 6.0 mm Xmax below 25.5 Hz. The radiator peaks at 6.0 mm near 33.2 Hz, 32% of its 19.0 mm. Which one runs out first depends on the pair: a radiator with less area or travel can be the limit.
What you set#
Choose Passive radiator in Type at the top of the enclosure panel. Its fields are:
| Field | What it sets |
|---|---|
| Volume | The net internal volume: the air behind the cone, not counting the driver or bracing. |
| Added mass (tuning) | Grams added to each radiator, from 0 to 500 g. More mass, lower tuning. |
| Passive radiator | Which radiator. Click Select a passive radiator… and type a brand or model, or choose Browse all with mechanical filters. Add makes a radiator from its own parameters. |
| Number of PRs | How many identical radiators, from 1 to 50. It appears once a radiator is chosen. |
| Results | Box tuning (Fb), Total PR mass (every radiator with its added mass) and, when you add volume under Box volume adjustments, Gross volume. |
When to use it#
Good for#
- A low tuning in a small box, where a port would not fit: the 10 L box above needs a 43.7 cm port, a radiator only a hole in the baffle.
- No port noise: there is no jet of air to chuff.
- Tuning you can change after the build, by adding or removing mass.
Watch for#
- The notch below the tuning, near the radiator’s own resonance: the output falls away faster there than with a port.
- A stiff radiator, or one whose own resonance is close to the tuning: it loses the deep bass a port would give.
- Two limits instead of one: the cone below the tuning and the radiator around it. Check both at the power you plan to use.
Try it#
The passive radiator example at 20 W in the app’s own tiles, with 50 g added and then 2 radiators.
To keep going, open the passive radiator example in the simulator: the Dayton Audio DCS165-4 and one Dayton Audio E150HE-PR in 10 L, as on this page. Change Added mass (tuning) and watch Box tuning (Fb) follow.
Tiles to watch#
Ask your AI#
Ask your AI
Using 00 Simulator, for the passive radiator box in my open workspace, try 25 g and 50 g of added mass without saving. Tell me each option’s tuning, F3, and peak passive radiator excursion at its set power against the radiator’s Xmax.
Connect your assistant so it can open your designs.