# Passive radiator > How a passive radiator box works in 00 Simulator: tuning with added mass, choosing a radiator, PR Excursion, and the fields to set. Source: https://simulator.00aud.io/docs/boxes/passive-radiator A passive radiator box is a vented box with a cone in place of the port: a driver with no motor, moved by the air in the box. Its mass does the port’s job, so you can tune a small box low without a port that will not fit, and with no port to chuff. _Figure: The passive radiator example as the Schematic tile draws it: the Dayton Audio DCS165-4 on the baffle, its rear loading a 10 L chamber that radiates through the Dayton Audio E150HE-PR._ The [passive radiator example](https://simulator.00aud.io/app?template=passive-radiator) in the [Schematic](https://simulator.00aud.io/docs/reference/tiles/schematic) tile: the Dayton Audio DCS165-4 and one Dayton Audio E150HE-PR in 10 L. The cone and the radiator both reach the room. The rear face loads the chamber, which radiates through a passive radiator. Cone and passive radiator both reach the room. ## 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: _Figure: SPL of the passive radiator example with 0, 25, 50, 100 g added to the radiator: more mass tunes the box lower._ Dayton Audio DCS165-4 and one Dayton Audio E150HE-PR in the 10 L passive radiator example, at 1 W, half space, 1 m. Simulated when this page was built. | Radiator | Fb | At 30 Hz | | --- | --- | --- | | No added mass, the example | 36 Hz | 65.7 dB | | 25 g added | 31.2 Hz | 71.3 dB | | 50 g added | 28 Hz | 73.6 dB | | 100 g added | 23.7 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: _Figure: SPL of the same driver and 10 L box tuned to about 35.4 Hz three ways: a port, the soft SB Acoustics SB15SFCR-00 with added mass, and the stiff Dayton Audio E150HE-PR._ Dayton Audio DCS165-4 in 10 L at 1 W, half space, 1 m. Simulated when this page was built. | Design | Fb | F3 | | --- | --- | --- | | 5 cm port | 35.4 Hz | 35.9 Hz | | SB Acoustics SB15SFCR-00, 50 g added | 35.4 Hz | 35.6 Hz | | Dayton Audio E150HE-PR, the example | 36 Hz | 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). > **A soft radiator with added mass tunes deep** As a rule, pick a radiator whose own resonance sits well below the tuning you want and whose Vas is larger than the box, then add mass to bring the tuning down. Pick one with enough area and travel too: it has to move the air a port would. ## 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](https://simulator.00aud.io/docs/reference/tiles/pr-excursion) tile draws its travel with a dashed **PR Xmax** line; read it beside the cone’s [Excursion](https://simulator.00aud.io/docs/reference/tiles/excursion) tile. The example at 20 W: _Figure: The cone's excursion and the radiator's PR Excursion for the passive radiator example at 20 W, each against its own Xmax._ | Case | Peak | At | Note | | --- | --- | --- | --- | | Cone, Dayton Audio DCS165-4 | 8.1 mm | 10 Hz | 8.1 mm at 10 Hz · Xmax 6.0 mm | | Radiator, Dayton Audio E150HE-PR | 6 mm | 33 Hz | 6.0 mm at 33.2 Hz · PR Xmax 19.0 mm | The passive radiator example at 20 W, half space, 1 m. Simulated when this page was built. 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 _Interactive walkthrough in the page: the simulator's own tiles running a short demo._ 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](https://simulator.00aud.io/app?template=passive-radiator) 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 - [SPL (dB)](https://simulator.00aud.io/docs/reference/tiles/spl): The tuning, the notch below it and F3. - [PR Excursion](https://simulator.00aud.io/docs/reference/tiles/pr-excursion): How far the radiator travels, against its own Xmax. - [Excursion](https://simulator.00aud.io/docs/reference/tiles/excursion): The cone, which still unloads below the tuning. - [Impedance](https://simulator.00aud.io/docs/reference/tiles/impedance): Two peaks, at 30.1 Hz and 54.9 Hz in the example, with a dip near the tuning between them. - [Max SPL (dB)](https://simulator.00aud.io/docs/reference/tiles/max-spl): How loud it can play before excursion or heat stop it. ## Ask your AI **Ask your AI** Your assistant tries the changes with the same solver, through the 00 Simulator connector, and saves nothing unless you ask. > 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.