• Use appropriate amount of damping material when designing. When a small airtight cabinet is filled with 50% (or more) damping material, it usually works well because it produces a smoother response and makes the speaker cabinet sound larger than it actually is. This helps to slightly extend the low frequency response. Medium or large enclosed boxes usually have enough volume without the need for large amounts of damping materials. In this case, the damping material is mainly used to suppress unnecessary standing waves and box resonance. Simply cover each surface in the box with damping material.
Open, band-pass, and passive radiator speakers are more sensitive to changes in cabinet volume, and damping materials are usually added only on each pair of parallel sides. The goal is to absorb box resonance without affecting the surface volume of the box. In addition, too much damping material will reduce the output of the duct. However, in practical applications, adding an appropriate amount of damping material will rarely cause any harm to the design of the passive radiator. The most damped parts of the cabinet are those surfaces behind or near the speaker unit.
• When using multiple speaker units, install the speaker units in a vertical direction with the best horizontal spreading angle. And install the speaker unit off-center, so that diffraction will be minimized. The following is an example of a three-way design:
Talking about the structure of the speaker box
It can usually be done by placing the speaker units with a shared crossover frequency as close as possible. Try to make the distance between their sound centers less than the wavelength of the crossover frequency. The tweeter should usually be located at the top, closest to the level of the ear, because the perception of most directions comes from the mid to high frequencies. The phase response of the crossover network has a great influence on the layout of the loudspeaker unit.
• If an opening or band-pass box structure is adopted, it is recommended to place the air duct in a position where there is no obstruction to the air in and out. A "rule of thumb" is to keep the end of the duct opening in the box at least one duct diameter away from any inner wall.