There are two types of bandpass boxes—single and double reflex. The first model has a sealed chamber at the rear end and a ported chamber at the front. The front is where the sound comes from.
And if you get one of these, here’s what you need to keep in mind. In a single reflex box, when the frequency is about 12 dB/octave, the transient rate is pretty good. This means that if you are trying to get the best quality of music in a small enclosure, you must pick the single reflex box.
This video from BudgetBassHead has a nice explanation of types.
Bandpass boxes have two chambers—one sealed and one ported chamber for a maximum slam and the woofer is mounted inside this box. The sound comes out of the ported side and is a lot louder than usual with a narrow frequency. So, in the right range, you get a great boom. This sound is great for hard rock, reggae, and rap music. But not all subs work well in bandboxes.
Ported boxes, also called reflex enclosures, are for those who like to listen to clear bass in rock, heavy metal, or hip-hop music. This one is built particularly to enhance the quality of bass but it is a bit of a task to tune it.
It comes in different sizes and takes up a lot of space. These boxes have multiple slots to allow the sound waves from the back to meet the ones in the front for better output. And because of that, the output level is increased around the tuning frequency. They give more output than sealed boxes.
Speaking of which, sealed boxes are the ones in which, as the name suggests, the sub is placed in an airtight box. This gives the bass the right kind of tone.
Also called acoustic suspension enclosures, these boxes are great for tracks with deep bass. It is a compact model but needs a lot of power. It has no ports or vents and the lower bass will roll off at a frequency range of 12 dB/octave.
It is sealed in the back and gets no output from there. These come in many shapes and sizes and are considered quite accurate sound enclosures.
Pros of a Bandpass Box
The sub doesn’t move too much which adds to the durability factor.
High-quality sound output along with external protection from wear and tear, which is very important in a moving car.
Gives a deep bass extension that other box designs don’t offer.
You have control over the output sound quality compared to regular speakers.
Helps move the cone according to the bandwidth of the frequency.
Very flexible thanks to the many customizations it offers to the user in terms of bandwidths and final sub-bass range.
Unlike sealed and ported types, bandpass boxes are not easy to design.
Produces deep bass output but not recommended for those who like upper bass output.
The sound comes only from the front, which makes it hard to detect problems with the sub.
Frequency response is uneven if the enclosure is small. This means there will be a distortion of some sounds in the final output.
Can blow up in no time if the problem with the speaker is not identified right away.
What Are Dual Bandpass Boxes?
A dual bandpass box or a double reflex box has a listening area that is connected to both the chambers in the front and the back with a port. In these types of bandpass boxes, the sound quality is good when the frequency ranges from 18 to 24 dB/octave. This means that if you are in a large space that does not have good transient features, you want to go for a dual reflex box.