# EQ and filters

> Add high-pass, low-pass, parametric, shelf and Linkwitz filters to an enclosure in 00 Simulator, edit them on the graph, and protect the cone.

Source: https://simulator.00aud.io/docs/guides/eq-and-filters

Every enclosure has its own filters, in **EQ / filters** in the Driver panel. They shape the signal before it reaches the driver, so the output, the cone’s travel and the port’s air speed all follow them. The filter most boxes need is a high-pass just below the tuning.

## The six filters

**Add**, in **EQ / filters**, offers six kinds. Here is each one’s own gain:

_Figure: Six small plots of filter gain against frequency: a high-pass and a low-pass at 24 dB per octave, a parametric boost and a narrower cut, a low shelf up and a high shelf down, and a Linkwitz transform that boosts the lowest octaves._

Worked out with the app’s own filter maths. High-pass, low-pass and Linkwitz transform at the settings **Add** gives them; the others with example gains, since they start at 0 dB.

| Filter | Settings | Gain |
| --- | --- | --- |
| High-pass filter | 30 Hz · BW 24 dB/oct | −3.0 dB at 30 Hz, −24.1 dB an octave below |
| Low-pass filter | 120 Hz · BW 24 dB/oct | −3.0 dB at 120 Hz, −24.1 dB an octave above |
| Parametric EQ | 100 Hz, +6 dB at Q 1 | +2.8 dB an octave either side |
| Parametric EQ | 100 Hz, −6 dB at Q 4 | −0.1 dB an octave either side |
| Low shelf | 80 Hz · +6 dB | +4.0 dB at 80 Hz, +5.8 dB at 20 Hz |
| High shelf | 200 Hz · −6 dB | −3.0 dB at 200 Hz, −5.8 dB at 1 kHz |
| Linkwitz transform | 50 Hz, Q 0.707 to 25 Hz, Q 0.5 | +7.9 dB at 20 Hz, +1.1 dB at 50 Hz |

| Filter | Shown as | What it does | Settings |
| --- | --- | --- | --- |
| **High-pass filter** | `HP` | Rolls off everything below the cutoff, so the cone and port are spared bass the box cannot play. | **Cutoff**, **Type**, **Slope** |
| **Low-pass filter** | `LP` | Rolls off everything above the cutoff, as a subwoofer’s crossover to the mains does. | **Cutoff**, **Type**, **Slope** |
| **Parametric EQ** | `PEQ` | A boost or a cut around one frequency. | **Center frequency**, **Gain**, **Q (bandwidth)** |
| **Low shelf** | `LS` | Raises or lowers everything below its frequency. | **Shelf frequency**, **Gain** |
| **High shelf** | `HS` | Raises or lowers everything above its frequency. | **Shelf frequency**, **Gain** |
| **Linkwitz transform** | `LT` | Moves a sealed box’s roll-off from its own resonance and Q to a lower, gentler one, with boost. | **Source F₀ (Fc)**, **Source Q₀ (Qtc)**, **Target Fp**, **Target Qp** |

- **Cutoff**, **Center frequency** and **Shelf frequency** run from 10 Hz to 20 kHz, **Gain** from −15 to +15 dB, and **Q (bandwidth)** from 0.1 to 16: lower is wider.
- The Linkwitz transform takes a sealed box’s resonance and Q as its source (20–200 Hz, Q 0.3–2) and moves them to a target (10–100 Hz, Q 0.3–1.5). For a sealed box the enclosure panel shows both, as its system resonance (Fsc) and system Q (Qtc).
- A new filter starts at a sensible frequency (30 Hz for a high-pass, 120 Hz for a low-pass, 100 Hz for parametric EQ) and at 0 dB where it has a gain, so it changes nothing until you set it.

## High-pass and low-pass slopes

A high-pass or low-pass has a **Type**, the filter family, and a **Slope**, how fast it falls in dB per octave. A new one is **BW** at 24 dB/oct. Change the **Type** and it keeps the nearest slope the new family has.

| Type | Slopes | At the cutoff | Good for |
| --- | --- | --- | --- |
| **BW** | 6, 12, 18, 24, 36 and 48 dB/oct | −3 dB | The flattest passband. The usual choice for a subsonic high-pass. |
| **LR** | 12, 24 and 48 dB/oct | −6 dB | Sums flat with the matching filter at a crossover, so it is the one to cross a subwoofer to mains with. |
| **Bessel** | 12 and 24 dB/oct | −3 dB | The gentlest phase, and the softest knee. |

_Figure: A high-pass at 30 Hz drawn in five slopes: Butterworth 12, 24 and 48 dB per octave, Linkwitz-Riley 24 and Bessel 24._

The same 30 Hz high-pass in five slopes. Steeper slopes cut harder below the cutoff and leave more above it; they also turn the phase further near the corner.

| Slope | At 30 Hz | An octave below |
| --- | --- | --- |
| BW 12 dB/oct | −3.0 dB | −12.3 dB |
| BW 24 dB/oct | −3.0 dB | −24.1 dB |
| BW 48 dB/oct | −3.0 dB | −48.2 dB |
| LR 24 dB/oct | −6.0 dB | −24.6 dB |
| Bessel 24 dB/oct | −3.0 dB | −13.4 dB |

## Add, switch off and copy

1. **Select the enclosure.** Click its row in the enclosure list. Filters belong to one enclosure. A [multiple-entry horn](https://simulator.00aud.io/docs/horns/multiple-entry-horn) keeps a set per driver: pick the driver with the chips above its filters.
2. **Open EQ / filters.** It is in the Driver panel on the right. Its header counts the filters that are on.
3. **Add one.** **Add** › the kind you want. The new filter opens with its settings; click any filter’s row to fold or unfold it. If you have clicked a graph to lock its cursor, the new filter goes in at that frequency.
4. **Switch off or delete.** The tick box on a filter’s row turns it off and keeps its settings, the quick way to see what it does. The bin deletes it.

**Copy from...** appears once another enclosure, or another driver of a multiple-entry horn, has filters. It opens **Copy filters from**: choose a set and a copy of it replaces this enclosure’s filters.

> **Order does not matter** At each frequency the app adds up the gain of every filter that is on, so the order of the list changes nothing, and there is no way to reorder it. The total boost counts up to +30 dB at any one frequency.

## Edit filters on the graph

**EQ** in a tile’s header (**Edit EQ on graph**) draws the selected enclosure’s filters on that tile as handles, and **Exit** puts the tile back. It is on **SPL (dB)**, **Max SPL (dB)**, **Headroom**, **Excursion**, **Port Velocity** and **Transfer Function Magnitude**. The **EQ Editor** tile has its handles out all the time.

- A high-pass or low-pass is a triangle on a dashed line: drag it sideways to move the cutoff. Click it for its editor, where the `HP` or `LP` chip flips it between the two, with the frequency, **Type**, **Slope** and **Delete**.
- Parametric EQ and shelves are a dot: drag it sideways for frequency and up or down for gain. Selected, it shows a handle either side; drag those to make it wider or narrower. A shelf’s chip flips it between low and high.
- Right-click a graph for **Add filter**: each kind, placed at the frequency you clicked. The tile switches to EQ and the new filter opens.
- On a multiple-entry horn the other drivers’ filters show as dashed chips along the top; click one to edit that driver’s filters.
- On a phone, tap a graph to lock the cursor, then **EQ here** adds a filter at that frequency, and a selected filter’s editor opens as a sheet: [On a phone](https://simulator.00aud.io/docs/guides/phone).

**Undo** (⌘/Ctrl+Z) takes back filter changes like any other edit.

## Protect the cone with a high-pass

Below its tuning a vented box stops holding the cone back, and excursion climbs fast. In the 55 L vented example at 200 W, the Ciare 12.00SW passes its **13.5 mm** Xmax below 19 Hz. A 25 Hz high-pass at 24 dB/oct keeps it to **6.3 mm** and costs 0.6 dB at the 32 Hz tuning.

_Figure: Cone excursion of the vented example at 200 W with no filter, rising past Xmax below the tuning, and with a 25 Hz high-pass, staying well under it._

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 |
| High-pass 25 Hz, BW 24 dB/oct | 6.3 mm | 24 Hz |

_Figure: SPL of the same two runs: the high-pass takes the octave below the tuning away and leaves the tuning almost untouched._

The high-pass takes away the octave below the tuning, where the box makes little sound but the cone does most of its travelling.

| SPL (dB) | F3 | At 32 Hz | At 16 Hz |
| --- | --- | --- | --- |
| No filter | 30.3 Hz | 109.1 dB | 85.7 dB |
| High-pass 25 Hz, BW 24 dB/oct | 31.1 Hz | 108.5 dB | 70.4 dB |

The same box and power, 10 Hz to 200 Hz. 30 Hz is where **Add** puts a new high-pass.

| High-pass, BW 24 dB/oct | Peak excursion | Lost at 32 Hz | Peak port air speed |
| --- | --- | --- | --- |
| None | 21.2 mm and rising | 0 dB | 28.4 m/s |
| 20 Hz | 9.2 mm | 0.1 dB | 27.9 m/s |
| 25 Hz | 6.3 mm | 0.6 dB | 26.0 m/s |
| 30 Hz | 5.2 mm | 2.2 dB | 21.8 m/s |

- [Open the vented example](https://simulator.00aud.io/app?template=vented&power=200) at 200 W, add a **High-pass filter** and drag it on the **Excursion** tile until the curve sits under the Xmax line.
- Set it a little below the tuning. Higher protects more and costs more output at the tuning; the table shows the trade.
- A high-pass turns the phase, so group delay rises near the tuning: here from 26.7 ms to 41.7 ms at 32 Hz.

> **What the filters move, and what they do not** Filters change the drive, so **SPL (dB)**, **Excursion**, **Port Velocity**, **Cone Velocity**, **Phase** and **Group Delay** follow them, and **Headroom** counts them. **Impedance** and **Max SPL (dB)** do not change: Max SPL is the most each design can play before a limit, whatever the EQ.

## Ask your AI

**Ask your AI**

Your assistant runs the same solver on your own designs through the 00 Simulator connector, and can try filters without changing your workspace.

> Using 00 Simulator, try a 24 dB/oct Butterworth high-pass at a few frequencies below the tuning of each vented box in my open workspace, without saving. For each, tell me the peak excursion against the driver’s Xmax and how much output it costs at the tuning.