Bandpass Subwoofer Box Calculator

Size the rear chamber, front chamber, and port so your bandpass build fits the driver, the tuning target, and the cabinet footprint.

Bandpass results are based on net chamber volumes after subtracting driver displacement, bracing, and port volume.

📦 Real Bandpass Presets

⚙ Setup

Use imperial or metric inputs. The calculator converts chamber volumes, face area, and port area to keep the bandpass geometry consistent.

Bandpass goal

Balanced output keeps the two chambers closer together and suits mixed daily use.

Outer footprint shape

Rectangle footprints are the easiest way to frame a bandpass cabinet.

Face length (in)

Main face dimension for the enclosure footprint.

Face width (in)

Second face dimension for the footprint area.

Cabinet depth

Pick a fast depth target or switch to a custom depth for the actual cabinet stack.

Driver class

Use a common car-audio driver size band for the chamber estimate.

Driver count

Scale chamber volume for one driver or a matched pair.

Driver Fs (Hz)

Free-air resonance helps place the front chamber tune.

Driver Qts

Lower Qts drivers usually prefer a tighter bandpass split.

Driver Vas (ft³)

The calculator uses Vas as the main rear chamber reference.

Front chamber tune (Hz)

Front tune sets the peak output zone of the bandpass box.

Port style

Port style changes the end correction and the practical layout.

Front port area (in²)

Bigger areas lower air speed but usually need more length.

Wall thickness (in)

Panel thickness affects shell weight and the footprint stack.

Driver displacement (ft³)

Subtract the driver basket and motor volume from gross space.

Brace displacement (ft³)

Bracing matters in bandpass builds because both chambers are sensitive.

Overage buffer

Buffer keeps the final box from landing undersized after panels and fill.

Material type

Choose a material density profile for the shell-weight estimate.

Rear chamber net

0.00

ft³ / L

Front chamber net

0.00

ft³ / L

Front port length

0.0

in / cm

Gross design volume

0.00

ft³ / L

📊 Bandpass Spec Grid

0.00x

Rear factor

Vas multiplier for the rear chamber

0.00x

Front ratio

Front chamber size versus the rear

0.0 lb

Shell weight

Approximate shell mass from material and depth

0-0 Hz

Passband

Estimated loaded range from the selected tune

📒 Alignment Reference

Chamber ratio and tune ladder

Goal	Rear:Front	Tune window	Use case
Punch	1:0.55	38-48 Hz	Hard hit
Balanced	1:0.70	34-44 Hz	Daily mix
Deep	1:0.84	30-40 Hz	Lower end
SPL	1:0.95	40-54 Hz	Peak output

Driver class guide

Driver	Vas band	Qts band	Typical note
8 in	0.4-1.0 ft3	0.35-0.45	Compact
10 in	0.8-1.8 ft3	0.38-0.48	Street
12 in	1.8-4.0 ft3	0.40-0.52	Daily
15 in	4.0-8.0 ft3	0.42-0.55	Low end

Port area guide

Port style	Area / driver	Front tune	Bandpass use
Slot	30-45 in2	36-44 Hz	Punch
Round	24-36 in2	34-42 Hz	Clean
Flared	28-40 in2	32-40 Hz	Daily
Dual slot	40-70 in2	38-50 Hz	Loud

Footprint shape guide

Shape	Best for	Area formula	Note
Rectangle	Trunk builds	L x W	Easy to frame
Circle	Round shell	pi r2	Compact curve
Triangle	Wedge backs	0.5 b x h	Seatback fit
Custom	Odd panels	Direct area	Irregular face

💬 Bandpass Tips

Tip: Tune the front chamber first, then confirm the port fit.

Tip: Keep the port exit clear of the divider and rear wall.

A bandpass subwoofer enclosure consist of two separate internal chamber. Each of these internal chambers are referred to as either the rear chamber or the front chamber. The rear chamber is formed of the area in which the backwave of the subwoofer driver is contain.

The rear chamber dictate the compliance of the subwoofer driver. The front chamber is the chamber within which the port is contain, and it dictates the frequency range of the subwoofer enclosure. If the rear chamber is too large for the subwoofer driver, the subwoofer enclosure will lack control in the low frequencies.

Building a bandpass subwoofer box

If the rear chamber is too small for the subwoofer driver, the subwoofer enclosure may lack depth in its low frequency sound output. If the front chamber is too small in relation to the area of the port, the subwoofer enclosure will have a narrower range of low frequency sound output. If the front chamber is too large in relation to the area of the port, the subwoofer enclosure may lose output pressure.

In order to calculate the size of the rear and front chambers, you must calculate the parameters of the subwoofer driver. For instance, many people uses the Vas value for the subwoofer driver in order to determine the size of the rear chamber. Vas is the value of the compliance of the driver.

For instance, individuals that desire a subwoofer enclosure that produce a punchier (rather than deeper) sound may opt for the smaller rear chamber. Individuals that desire a deeper sounding subwoofer may opt for the larger rear chamber. The front chamber must be tune to a specific frequency, which the length of the port and the area of the port determine.

For example, a subwoofer enclosure that is to be use daily may have a front chamber with 70% of the volume of the rear chamber. However, a subwoofer enclosure that is to frequently produce high sound pressure levels may have a front chamber with nearly the same size than the rear chamber. In addition to the parameters of the subwoofer driver, you should consider the physical dimensions of the area in which the subwoofer enclosure is to be place.

The physical dimensions of the trunk or seatback area can limit the size of the subwoofer enclosure that is built. For instance, subtracting the volume of the subwoofer driver, the volume of the bracing, and the volume of the port from the total volume of the subwoofer enclosure can calculate the total internal volume of the subwoofer enclosure. Additionally, 10% of the total calculated volume can be subtracted from the total internal volume to account for the thickness of the bracing panels and the sound output components of the subwoofer enclosure.

Finally, the material from which the subwoofer enclosure is construct is also important. For instance, you can use materials like birch plywood to construct the subwoofer enclosure, as well as thick baffle. Regardless of the material that is selected, rigid bracing must be use.

The air pressure within a bandpass filter subwoofer enclosure is very high; high air pressures can cause the sides of the subwoofer enclosure to flex. If the sides of the enclosure flex, the subwoofer enclosure will lose efficiency and the sound may become distortedly. The port that is placed within the front chamber is also important.

Ports can be slot or round ports. Regardless of the type of port that is use, the area of the port should be large enough to allow the air to move through the subwoofer enclosure at sufficient rates to allow for efficient sound production, but not so large as to create air turbulence within the enclosure. Air turbulence within the subwoofer enclosure create a chuffing noise that is not desire when high quality sound is to be produce from the subwoofer enclosure.

The length of the port must be calculate with the desired tuning frequency of the subwoofer enclosure; the longer the port, the lower tuning frequency of the subwoofer enclosure. Finally, after the subwoofer enclosure has been construct, it should be test. For example, tone sweeps can be played through the enclosure to assess the frequency response of the subwoofer enclosure.

If the frequency response is not even within the low frequencies of the subwoofer enclosure, adjustment can be made to the subwoofer enclosure before it is complete. Thus, successful construction of a bandpass subwoofer enclosure require an understanding of the math behind its construction, the material necessary to build it, and the volumes of each of its chambers.