# Limits: travel, heat and air

> The three limits that stop a speaker getting louder (cone travel, voice coil heat and port air speed) and where 00 Simulator shows each one.

Source: https://simulator.00aud.io/docs/start/limits

Three things stop a speaker getting louder: the cone runs out of travel, the voice coil gets too hot, or the air in the port moves too fast. 00 Simulator draws each one. Max SPL combines travel and thermal limits; Headroom also checks port air speed. Which comes first depends on the design and the frequency.

- **Travel:** Cone excursion against Xmax, on the **Excursion** tile. Worst below the tuning of a ported box.
- **Heat:** The power into the voice coil against its rating, Pe, on the **Max SPL (dB)** tile.
- **Air:** Air speed in the port against 17 m/s, on the **Port Velocity** tile.

## Travel: Xmax, Xmech and Xdamage

_Figure: The Excursion tile for the vented example at 200 W, with and without a 25 Hz high-pass, against the driver’s 13.5 mm Xmax._

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.

| Excursion | Peak | At |
| --- | --- | --- |
| No filter | 21.2 mm | 10 Hz |
| 25 Hz high-pass | 6.3 mm | 24 Hz |

At 200 W the [vented example](https://simulator.00aud.io/app?template=vented&power=200) passes its 13.5 mm Xmax below 18.7 Hz, reaching 21.2 mm. At the 32 Hz tuning the port does the work and the cone moves only 2.5 mm. Below the tuning the box stops holding the cone, which is why a high-pass there helps: with a 25 Hz high-pass the peak falls to 6.3 mm.

The lines hide when **Show Xmax reference lines** is off in **Settings › Simulation…**.

| Figure | What it means | On the Excursion tile |
| --- | --- | --- |
| Xmax | Maximum linear excursion, one way. Past it the motor and suspension stop behaving linearly and distortion rises. A clean-playing limit, not damage. | Dashed line in the enclosure’s colour |
| Xmech | The mechanical limit, where the surround or spider bottoms. Optional in the driver’s data. | Dotted line |
| Xdamage | Travel that can physically damage the driver. Optional in the driver’s data. | Finely dotted line |

Passive radiators have their own Xmax, on the **PR Excursion** tile, and it caps Max SPL too. A passive radiator can run out of travel while the driver is still inside its own.

## Heat: Pe and the thermal rules

Pe is the power the maker rates the driver for, 2,000 W for the Ciare 12.00SW. What damages a voice coil is heat, and a loudspeaker is not a resistor: its impedance swings with frequency, so the same watts mean a different voltage, current and heat at every frequency. The Max SPL tile reads the rating one of three ways, chosen under **Thermal limit** in its settings:

| Rule | What it holds at the limit | For the Ciare 12.00SW |
| --- | --- | --- |
| Real input power, the default (as in Hornresp) | The real power going into the driver, at its rating. The voltage climbs at impedance peaks. | 2,000 W |
| Constant voltage (as in WinISD) | One amplifier voltage at every frequency: by default √(Pe × Re), the rated power into the coil’s resistance. | 81.2 V |
| Coil heating (an estimate) | The heat in the voice coil, at a budget: the heat the driver took in its own rating test, re-created in the model with pink noise over 30–300 Hz. | 1,029 W, 51% of the rating |

The coil heating budget is well under the rating because a power rating counts watts against the lowest impedance in its test band, while most of the band sits at higher impedance. **Voice coil temperature** (20–300 °C) raises Re for every rule: at 150 °C a copper coil’s resistance is 51% higher, which lowers the output where the impedance is close to Re. It applies to Max SPL only; the SPL tile stays cold.

_Figure: The Max SPL tile for the vented example with Limits on: the Max SPL line and the two ceilings it follows, the power limit dashed and Xmax dotted._

The same vented example, half space, 1 m. Max SPL does not depend on the input power you set. Simulated when this page was built.

| Frequency | Max SPL | Power limit ceiling | Xmax ceiling |
| --- | --- | --- | --- |
| 20 Hz | 93.7 dB | 111.3 dB | 93.7 dB |
| 32 Hz | 120.7 dB | 120.7 dB | 123.6 dB |
| 50 Hz | 117.9 dB | 127.4 dB | 117.9 dB |
| 100 Hz | 122.4 dB | 122.4 dB | 125.4 dB |
| 200 Hz | 121.3 dB | 121.3 dB | 137.1 dB |

Turn on **Limits** in the Max SPL tile’s header to draw both ceilings; the line is the lower of the two. In this box it follows Xmax below 30.9 Hz, heat from 30.9 to 34.8 Hz, Xmax from 34.8 to 86.6 Hz and heat above 86.6 Hz: heat takes over around the tuning, where the cone barely moves. Your input power and EQ do not move the line: they change what you send, not what the speaker can take. Port air speed is not part of Max SPL.

## Air: port velocity

Air through a port gets noisy when it moves too fast: it chuffs and whistles. The **Port Velocity** tile draws its peak speed at each frequency against a dashed warning line, 17 m/s by default. At 200 W the vented example’s port peaks at 28.4 m/s near 30.1 Hz, over the line. Air speed follows the square root of power: at a quarter of the power, 50 W, it peaks at 14.2 m/s.

- Change the warning line with **Port velocity** under **Settings › Simulation…**, from 10 to 30 m/s. The app’s hint puts the typical limit at 15 to 20 m/s, higher for flared ports.
- More port area lowers the speed; the port then gets longer to keep the tuning. [Fix a noisy port](https://simulator.00aud.io/docs/guides/noisy-port) walks through it.
- A sixth-order bandpass box has a second port, on the **Port Velocity (Rear Chamber)** tile.

## All three at once: Max SPL and Headroom

In this example the port is the tightest limit in the band the box plays: at 200 W it is over its line at the tuning, while the cone passes Xmax only below 18.7 Hz, beneath the box’s 30.3 Hz F3, and the power is 10% of Pe. Another design can be the other way round, which is why two tiles combine the limits:

- **Max SPL (dB)** shows the loudest each design can play at each frequency, a sine at a time, before Xmax or the thermal rule stops it. It ignores port air speed.
- **Headroom** starts from a listening target, an average level plus a crest factor for the peaks (85 dB and 12 dB by default), and colours each frequency **Clean**, **Threshold** or **Over max** against all the limits, port air speed included.

The Headroom tile’s default limits. Change them under **Limits** in its settings.

| Limit | Clean up to | Over max above |
| --- | --- | --- |
| Driver excursion | 1 × Xmax | 1.125 × Xmax |
| Port velocity | 17 m/s | 30 m/s |
| Thermal power | 0.5 × Pe | 1 × Pe |
| PR excursion | 1 × PR Xmax | 1.25 × PR Xmax |

> **What the limits leave out** The model is linear. A real driver’s motor and suspension soften as it nears Xmax, a hot coil compresses the output, and a port compresses before it chuffs. Each frequency is checked as a steady sine, while music spreads its energy and shares one thermal budget. Treat the lines as warnings to design away from, not ratings to run up to.

## Ask your AI

**Ask your AI**

Your assistant runs the same solver at other powers through the 00 Simulator connector, without changing your design.

> Using 00 Simulator, for each enclosure in my open workspace, find the input power at which the cone first reaches Xmax and the power at which the port passes 17 m/s, without saving, and tell me which limit comes first and at what frequency.