# Horn Acoustic Impedance

> Read local acoustic loading as pressure divided by volume flow, distinguish magnitude and complex components, and recognise zero-flow singularities.

Source: https://simulator.00aud.io/docs/reference/tiles/horn-acoustic-impedance

Horn Acoustic Impedance describes the acoustic load at a station: local pressure divided by local volume flow. It is useful for understanding the horn’s loading, rather than choosing an amplifier.

- **Shows:** Pressure divided by volume flow at a horn station, as magnitude, phase, resistance or reactance.
- **Healthy when:** You are reading the intended station and distinguishing acoustic loading from the amplifier’s electrical load.
- **If it is not:** Compare pressure and velocity there, or choose another station if volume flow vanishes.

## The tile

_Figure: Horn Acoustic Impedance at Main H2 mouth, Main H4 mouth in the tapped-horn example._

Tapped-horn example at 100 W, half space, 1 m. Stations are measured from the closed end. Simulated when this page was built.

| Station | Position | Area | Peak | At |
| --- | --- | --- | --- | --- |
| Main H2 mouth | 0.95 m | 600 cm² | 35.53 kPa·s/m³ | 49.9 Hz |
| Main H4 mouth | 2.50 m | 2,400 cm² | 1.99 kPa·s/m³ | 392.4 Hz |

The example compares a narrow station with the mouth; its axis uses kPa·s/m³ to keep the values readable. In the app choose the station and then the display mode. Electrical **Impedance**, in ohms, is a different tile.

| Mode | Meaning |
| --- | --- |
| **Magnitude** | The size of the pressure-to-flow ratio, in Pa·s/m³. |
| **Phase** | The phase angle of pressure relative to volume flow, in degrees. |
| **Resistance** | The real part of the acoustic impedance. |
| **Reactance** | The imaginary part, which can change sign around resonances. |

## A closed end needs care

At exactly zero volume flow the ratio is undefined and the solver can leave it absent. Very small numerical flow can instead give an extremely large ratio. A closed-end throat is therefore a poor starting station for a readable impedance comparison; choose a station farther along the path.

The sign convention treats flow towards the stored segment end as positive. Keep the same location and orientation when comparing resistance, reactance or phase. A missing matching station in another enclosure is omitted, not represented by zero.

> **Read the numerator and denominator** A large ratio can come from high pressure, small flow, or both. Check **Horn Pressure** and **Horn Particle Velocity** at the same station before deciding what to change.

## What moves it

| Change | Effect |
| --- | --- |
| Input power alone | Pressure and flow scale together, so the linear ratio is unchanged. |
| Path length, area or flare | Changes resonances and the load seen at a station. |
| Stuffing or chamber losses | Changes the dissipative and reactive behaviour. |
| Selected station | Reads a different local load within the same horn. |

## What to try

| Try | What it changes |
| --- | --- |
| Separate the components | Switch between **Magnitude**, **Phase**, **Resistance** and **Reactance**. |
| Explain a gap | A station with no flow has no defined acoustic impedance; a missing value is not zero. |
| [Check amplifier load elsewhere](https://simulator.00aud.io/docs/reference/tiles/impedance) | Use **Impedance** for electrical impedance in ohms. |

## Ask your AI

**Ask your AI**

> Using 00 Simulator, inspect the acoustic impedance of my horn at a non-zero-flow station and at the mouth. Explain the magnitude, resistance and reactance in the working band, using the pressure and volume flow to explain any extreme values.