# Bandpass 6

> How a sixth-order bandpass box works in 00 Simulator: two ported chambers, two tunings, and what porting the rear chamber adds and costs.

Source: https://simulator.00aud.io/docs/boxes/bandpass-6

A sixth-order bandpass ports both chambers. The driver sits between them, each chamber has its own port and tuning, and both ports reach the room. This page shows what the second port adds, what each tuning does and which limits it brings, on the bandpass example with its rear chamber ported.

_Figure: A sixth-order bandpass drawn by the simulator’s schematic: the driver between two chambers, each with a port to the room._

The design this page uses, as the **Schematic** tile draws it: the bandpass example’s 70 L rear chamber tuned to 30 Hz through a 10 cm port, and its 50 L front chamber tuned to 70 Hz.

The driver sits between a rear chamber vented through a port and a front chamber that radiates through a port. Only the chamber outlets reach the room.

## How it works

Each chamber and the air in its port is a resonator. The rear one, tuned low, holds up the bottom of the band, as a vented box’s port does. The front one, tuned higher, holds up the top and rolls off above it. Both ports radiate, and the room hears their sum.

- **Passband (−3 dB):** 41.9–98 Hz
- **Loudest:** 115.4 dB at 66.5 Hz, from 100 W
- **Rear chamber:** 70 L, tuned to 30 Hz: one 10 cm port, 31.2 cm long
- **Front chamber:** 50 L, tuned to 70 Hz: one 15 cm port, 12.5 cm long

> **Keep the two tunings apart** The cone pushes the air in one chamber as it pulls the air in the other. Two identical chambers would make equal and opposite outputs that cancel, and the box would be silent.

## What porting the rear adds

Seal the rear chamber of this box and it is a fourth-order bandpass with the same chambers and front tuning. Porting the rear lowers the bottom of the band from 48.2 Hz to 41.9 Hz.

_Figure: The same 70 L and 50 L chambers, front tuned to 70 Hz, with the rear chamber sealed and with it ported: the ported rear lowers the bottom of the band._

B&C 18SW115 in 70 L rear and 50 L front chambers, at 100 W, half space, 1 m. Simulated when this page was built.

| Design | Band |
| --- | --- |
| Rear sealed (Bandpass 4) | 48.2–105 Hz |
| Rear tuned to 30 Hz (Bandpass 6) | 41.9–98 Hz |

The cost is below the rear tuning. There, as in a vented box, the port no longer holds the cone back: at 100 W the cone reaches 12.5 mm at 10 Hz, against 4.6 mm with the rear sealed and the driver’s 14.0 mm Xmax.

_Figure: Cone excursion of the same two boxes against the driver's 14.0 mm Xmax: below the rear tuning the ported box's cone is no longer held._

B&C 18SW115 in 70 L rear and 50 L front chambers, at 100 W, half space, 1 m. Simulated when this page was built.

| Design | Peak |
| --- | --- |
| Rear sealed (Bandpass 4) | 4.6 mm at 10 Hz |
| Rear tuned to 30 Hz (Bandpass 6) | 12.5 mm at 10 Hz |

## The two tunings

The front tuning moves the band, as in a fourth-order box, and a higher one is louder.

_Figure: The 6th-order box with its front chamber tuned to 55 Hz, 70 Hz, 85 Hz and its rear chamber at 30 Hz: the band follows the front tuning._

B&C 18SW115 in 70 L rear and 50 L front chambers, at 100 W, half space, 1 m. Simulated when this page was built.

| Design | Band | Peak |
| --- | --- | --- |
| Front tuned to 55 Hz | 34.4–70.7 Hz | 113.7 dB |
| Front tuned to 70 Hz | 41.9–98 Hz | 115.4 dB |
| Front tuned to 85 Hz | 54.5–118 Hz | 118.6 dB |

The rear tuning moves the band much less. It sets where the rear port stops holding the cone: tuned lower, the cone moves less at 20 Hz.

B&C 18SW115 in 70 L rear and 50 L front chambers, at 100 W, half space, 1 m. Simulated when this page was built. Front chamber tuned to 70 Hz.

| Rear tuning | Band (−3 dB) | Rear port, peak | Cone at 20 Hz |
| --- | --- | --- | --- |
| 25 Hz | 43.1–100 Hz | 19.6 m/s at 15.4 Hz | 3.3 mm |
| 30 Hz | 41.9–98 Hz | 19.8 m/s at 19.6 Hz | 5.7 mm |
| 40 Hz | 43.9–91.2 Hz | 21.0 m/s at 37.4 Hz | 7.1 mm |

## What you set

Choose **Bandpass 6** as the **Type** when you add an enclosure; the enclosure panel lists it as **6th-order BP**. Pick a chamber with the **Front** and **Rear** tabs beside **Chamber**. Both tabs now have the same controls:

| Control | What it sets |
| --- | --- |
| **Loading** | **Port**, or **Passive radiator** to load that chamber with a radiator instead of a port. |
| **Front volume** / **Rear volume** | The net air in the chamber. |
| **Tuning** | The chamber’s own tuning. |
| **Port length** | Its port’s length: change the tuning and the length follows, or type a length and the tuning follows. |
| **Port** | **Shape**, **Number of ports**, size and **Advanced** › **End correction**. The two ports share one end correction: change it on either tab and both follow. |
| **Results** | **Cross-sectional area** and **Port volume** for that chamber’s port, and its **1st front-port resonance** or **1st rear-port resonance**. |

- Switch between **4th-order BP** and **6th-order BP** and the front chamber stays as it is: only the rear chamber changes. The bandpass example switched to sixth order gets a rear port tuned to 40 Hz through a 7.6 cm port, the rear settings it already carried.
- A box with no front chamber yet gets one at half its volume, tuned 1.4 times higher, so the two chambers never start out identical: the vented example becomes 55 L tuned to 32 Hz behind the cone and 27.5 L tuned to 44.8 Hz in front.
- With a driver chosen, the **Add enclosure** dialog starts **Bandpass 6** from the driver itself: 1.5 times its Vas behind the cone, tuned to 0.9 × Fs, and half that volume in front, tuned to 1.4 × Fs. For the B&C 18SW115 that is 223.6 L and 111.8 L.

## What to check

- **Port Velocity (Rear Chamber)**: the rear port carries the deep bass. At 100 W it peaks at 19.8 m/s near 19.6 Hz, over the 17 m/s warning line. Two rear ports keep the tuning and bring it to 9.9 m/s, each 68.3 cm long.
- **Port Velocity**: the front port. It peaks at 12.3 m/s near 59 Hz.
- **Excursion** below the rear tuning, as for a vented box. A high-pass filter below 30 Hz keeps the cone from moving for output the box does not make. See [EQ and filters](https://simulator.00aud.io/docs/guides/eq-and-filters).
- Port resonances, under **Results**: the rear port’s first resonance is at 551 Hz and the front one’s at 1,373 Hz, far above the band. Longer ports resonate lower: with two rear ports it falls to 251 Hz.

- [Port Velocity (Rear Chamber)](https://simulator.00aud.io/docs/reference/tiles/rear-port-velocity): The rear port’s air speed against the warning line.
- [Port Velocity](https://simulator.00aud.io/docs/reference/tiles/port-velocity): The front port’s air speed.
- [Excursion](https://simulator.00aud.io/docs/reference/tiles/excursion): The cone’s travel against Xmax.

## When to use it

### Good for

- A lower bottom to the band from the same chambers: here 41.9 Hz instead of 48.2 Hz with the rear sealed.
- Setting each edge of the band with its own tuning.
- Loud bass with the driver hidden inside, from ports on both chambers.

### Watch for

- Two ports to size and fit. In this design the rear one is the first over the warning line.
- The cone is let go below the rear tuning: use a high-pass filter.
- Tunings too close together cancel.
- For a cone held by a sealed rear chamber instead, see [Bandpass 4](https://simulator.00aud.io/docs/boxes/bandpass-4).

## Try it

_Interactive walkthrough in the page: the simulator's own tiles running a short demo._

This page’s design at 100 W in the simulator’s own tiles: the front tuning, then a second rear port.

There is no sixth-order example yet. Open the bandpass example and set **Type** to **6th-order BP**, then on the **Rear** tab set **Tuning** to 30 Hz and the port’s **Diameter** to 10 cm, and on the **Front** tab set **Tuning** to 70 Hz. That is this page’s design.

- [Open the bandpass example](https://simulator.00aud.io/app?template=bandpass&power=100): The fourth-order example at 100 W, to switch to sixth order.

## Ask your AI

**Ask your AI**

Your assistant runs the same solver on your own designs through the 00 Simulator connector.

> Using 00 Simulator, for each sixth-order bandpass box in my open workspace, check both ports' peak air speed at the saved power. For any port above 17 m/s, try a second port of the same size without saving, and tell me the new air speed, each port's length and whether the −3 dB band changed.