Boxes · Types
TYPEPORTED REARPORTED FRONTBandpass 6
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
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.
SPL
dB
- Rear sealed (Bandpass 4)Band 48.2–105 Hz
- Rear tuned to 30 Hz (Bandpass 6)Band 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.
Excursion
mm
- Rear sealed (Bandpass 4)Peak 4.6 mm at 10 Hz
- Rear tuned to 30 Hz (Bandpass 6)Peak 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.
SPL
dB
- Front tuned to 55 HzBand 34.4–70.7 Hz · Peak 113.7 dB
- Front tuned to 70 HzBand 41.9–98 Hz · Peak 115.4 dB
- Front tuned to 85 HzBand 54.5–118 Hz · Peak 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.
| 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.
- 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.
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.
Try it#
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.
Ask your AI#
Ask your AI
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.
Connect your assistant so it can open your designs.