# PR Excursion

> Check each passive radiator’s travel against its own Xmax, and understand why count and added mass change both travel and tuning.

Source: https://simulator.00aud.io/docs/reference/tiles/pr-excursion

A passive radiator can run out of travel while the powered cone is barely moving. This tile checks the radiator separately, against its own Xmax.

- **Shows:** How far each passive radiator travels, peak and one way, in mm at each frequency, against its own Xmax.
- **Healthy when:** The curve stays under the PR Xmax line at the power you will use, and the driver stays under its own Xmax on **Excursion**.
- **If it is not:** More radiators, a radiator with more travel, or less power.

## The tile

_Figure: Passive radiator travel at two powers and with two radiators, against the radiator’s own Xmax._

Passive radiator example at 50 W, half space, 1 m. Simulated when this page was built.

| PR Excursion | Peak | At |
| --- | --- | --- |
| One radiator | 9.5 mm | 33 Hz |
| Two radiators, same mass each | 6.1 mm | 37 Hz |
| One radiator, 25 W | 6.7 mm | 33 Hz |

The single radiator peaks at 9.5 mm near 33.2 Hz at 50 W. The curve is peak, one-way travel per radiator. [Open this example](https://simulator.00aud.io/app?template=passive-radiator&power=50).

The dashed PR Xmax line belongs to the passive radiator, not the powered driver. Check **Excursion** alongside it. With passive radiators in both chambers of a bandpass box, the main curve is the larger front or rear travel at each frequency, and the limit lines identify their chamber roles.

## Count and mass must be considered together

In this comparison, two identical radiators with unchanged mass each peak at 6.1 mm near 37.4 Hz. Adding a radiator changes the tuning as well as the available area, so it is not a comparison at the same alignment.

| Change | What to check next |
| --- | --- |
| Increase **Number of PRs** | Recheck the new tuning, the response shape and each radiator’s travel. |
| Increase **Added mass (tuning)** | Tuning falls; recheck peak travel and the powered cone below tuning. |
| Choose a radiator with more Xmax or area | Confirm its mass, compliance and mounting space as well as travel. |
| Reduce power | Both radiator and driver motion fall; compare the remaining SPL. |

> **Check the weakest moving part** Passing the powered driver’s Xmax check does not make the radiator safe. **Headroom** checks both when their limits are available.

## What to try

| Try | What it changes |
| --- | --- |
| [Use two radiators](https://simulator.00aud.io/docs/boxes/passive-radiator) | Set **Number of PRs** to 2. They share the work, so each travels less, and the tuning rises. |
| [Mind the added mass](https://simulator.00aud.io/docs/boxes/passive-radiator#added-mass) | More **Added mass (tuning)** tunes the box lower and can increase peak travel; recheck both the radiator and powered cone. |
| Less power | Travel follows the square root of power: half the power is about 0.7 times the excursion. |

## Ask your AI

**Ask your AI**

> Using 00 Simulator, check the driver and passive radiator excursion in my design at its current power. Preview a second identical radiator, report how tuning and peak travel change, and do not save the change yet.