# Glossary

> Plain definitions of loudspeaker, enclosure, horn and measurement terms used in 00 Simulator.

Source: https://simulator.00aud.io/docs/reference/glossary

Short definitions of the terms you meet when designing an enclosure. Follow the links for the controls, graphs and worked examples behind them.

## Response and level

<a id="spl"></a>

**SPL** (sound pressure level): Sound pressure expressed in decibels at the chosen listening distance and radiation space. The [SPL tile](https://simulator.00aud.io/docs/reference/tiles/spl) shows the response at the input power you set.

<a id="f3"></a>

**F3** (−3 dB point): A frequency where the response is below its reference level by 3 dB. Read it with the response shape: a peak can make a single cutoff figure misleading. [Reading a response](https://simulator.00aud.io/docs/start/reading-a-response).

<a id="f6-f10"></a>

**F6 and F10**: Cutoff markers like F3, but at drops of 6 dB and 10 dB. They show how the low-frequency roll-off continues beyond F3.

<a id="phase"></a>

**Phase**: The angle of an oscillating response relative to the drive. Outputs add with their phase, so similar levels can reinforce or cancel. [Phase](https://simulator.00aud.io/docs/reference/tiles/phase).

<a id="group-delay"></a>

**Group delay**: How quickly phase changes with frequency, expressed as a time. It describes the modelled response and filters, not a separate echo from the room. [Group Delay](https://simulator.00aud.io/docs/reference/tiles/group-delay).

<a id="impedance"></a>

**Impedance**: The frequency-dependent electrical load, with both magnitude and phase. It includes resistance, coil inductance and the driver’s movement against its acoustic load. [Impedance](https://simulator.00aud.io/docs/reference/tiles/impedance).

<a id="baffle-step"></a>

**Baffle step**: The broad level change as wavelengths become large compared with the baffle. The app’s optional model is a smooth correction, not a full diffraction simulation. [Baffle Layout](https://simulator.00aud.io/docs/reference/tiles/baffle-layout).

## Driver and limits

<a id="ts-parameters"></a>

**T/S parameters** (Thiele/Small parameters): Small-signal measurements that describe a driver’s motor, moving mass, suspension and damping. See the [parameter reference](https://simulator.00aud.io/docs/reference/ts-parameters) for the symbols and units.

<a id="fs"></a>

**Fs**: The driver’s free-air resonance frequency, before the enclosure adds its acoustic load.

<a id="qts"></a>

**Qts**: The total quality factor of the driver’s free-air resonance, combining electrical and mechanical damping. It is not the Q of the finished box.

<a id="vas"></a>

**Vas**: The volume of air with the same compliance as the driver’s suspension. It is a property of the driver, not a recommended box size.

<a id="sd"></a>

**Sd**: The effective area of the moving piston. Cone velocity multiplied by Sd gives volume velocity.

<a id="excursion"></a>

**Excursion**: The cone’s displacement from its resting position. The [Excursion tile](https://simulator.00aud.io/docs/reference/tiles/excursion) reports peak, one-way movement.

<a id="xmax"></a>

**Xmax**: The manufacturer’s maximum linear one-way excursion. Passing it warns that the small-signal model no longer describes the driver reliably; it is not itself a prediction of damage.

<a id="pe"></a>

**Pe**: The driver’s rated power handling. [Max SPL](https://simulator.00aud.io/docs/reference/tiles/max-spl) interprets it through the selected thermal rule.

<a id="max-spl"></a>

**Max SPL**: The modelled sound level at which excursion or the chosen thermal ceiling is reached, one frequency at a time. Port air speed is checked separately. [Max SPL](https://simulator.00aud.io/docs/reference/tiles/max-spl).

<a id="headroom"></a>

**Headroom**: The margin between the demanded level and a limit. The [Headroom tile](https://simulator.00aud.io/docs/reference/tiles/headroom) compares average and peak demand with clean and maximum thresholds.

<a id="crest-factor"></a>

**Crest factor**: The difference between average and peak level. It lets the headroom calculation separate sustained thermal demand from brief peaks.

## Boxes and ports

<a id="alignment"></a>

**Alignment**: The response produced by a particular driver, box volume, tuning and losses together. A box size alone is not an alignment.

<a id="net-volume"></a>

**Net volume**: The air volume available to the acoustic chamber, excluding the space occupied by the port, driver and other objects. [From simulation to a build](https://simulator.00aud.io/docs/start/simulation-to-build).

<a id="gross-volume"></a>

**Gross volume**: The internal cabinet volume needed to contain the net air volume plus the port and entered displacements. It does not include wall thickness.

<a id="qtc"></a>

**Qtc**: The total Q of a driver in a sealed box. It describes the damping and shape around the system resonance. [Sealed](https://simulator.00aud.io/docs/boxes/sealed).

<a id="fb"></a>

**Fb** (tuning frequency): The resonance of the air in a port against the chamber air, or the corresponding tuning of a passive radiator system.

<a id="end-correction"></a>

**End correction**: The allowance for air moving just beyond the ends of a duct. It makes the acoustic length greater than the physical length. [Ports and end correction](https://simulator.00aud.io/docs/boxes/ports).

<a id="port-velocity"></a>

**Port velocity**: Peak air speed through the port opening. It is a useful warning for noise and compression, which the linear model does not calculate directly. [Port Velocity](https://simulator.00aud.io/docs/reference/tiles/port-velocity).

<a id="volume-velocity"></a>

**Volume velocity**: Volume flow per unit time, equal to particle velocity multiplied by cross-sectional area. The same flow moves faster in a narrower passage.

<a id="passive-radiator"></a>

**Passive radiator**: An undriven diaphragm that replaces the moving air mass of a port. Its mass tunes the system and its travel needs checking. [Passive radiator](https://simulator.00aud.io/docs/boxes/passive-radiator).

## Horns

<a id="throat"></a>

**Throat**: The start of a horn path, normally its smallest cross-section.

<a id="mouth"></a>

**Mouth**: An opening where the path radiates into the surrounding space. Mouth area and radiation space affect the load seen by the path.

<a id="flare"></a>

**Flare**: The change of cross-sectional area along a segment. The horn editor can join segments with different profiles. [Horn Editor](https://simulator.00aud.io/docs/reference/tiles/horn-editor).

<a id="tapped-horn"></a>

**Tapped horn**: A horn with both faces of the driver coupled into one path at different positions. Their outputs combine with a frequency-dependent phase relationship. [Tapped horn](https://simulator.00aud.io/docs/horns/tapped-horn).

<a id="particle-velocity"></a>

**Particle velocity**: The local speed of air in a horn section. It differs from volume velocity because it also depends on the section area. [Horn diagnostics](https://simulator.00aud.io/docs/horns/diagnostics).

<a id="fold"></a>

**Fold**: A cabinet arrangement that fits the acoustic path into a smaller footprint. The acoustic simulation follows the path geometry rather than calculating three-dimensional flow around each bend. [Folding](https://simulator.00aud.io/docs/horns/folding).