Double bass array


A double bass array is a specific layout of subwoofers within a rectangular listening space. It removes unwanted room related resonances over a wide listening area.

Preface

A DBA requires at least two subwoofers that are placed at opposing walls in a specific layout. The subwoofer array on the back wall is inverted and delayed based on the distance to the frontal subwoofer array. This will actively "absorb" any reflected sound.

Design

Array layout

Modes between side walls, floor and ceiling are suppressed by arranging the subwoofer in a specific grid:
Counter
With this specific grid layout reflections from the walls act as mirror sources. Interference of the subwoofers and mirror sources create a plane wave up to a certain frequency. The more sources the higher the frequency. This cutoff frequency can be calculated for each dimension as follows:
Example: A 2 × 2 array on a wall measuring 4 × 3 m would work up to 86Hz horizontally and up to 114Hz vertically.

Active Absorption

Due to the specific grid layout of the subwoofer array most modal effects are suppressed. The length modes on the other hand get fully excited. The array on the back wall will emit a polarity inverted wave at the very same moment the wave from the front wall hits the back wall. Reflection and inverted wave will interfere with each other destructively so the reflection is canceled. This is also known as "active absorption".
The necessary delay of the back array is based on the length of the room:
The necessary delay required for a DBA is available in most digital equalizers or digital crossovers. Polarity of the back array can easily be achieved by inverting the signal coming from the amps or by swapping the cables going to the driver. Most active subwoofers also offer a polarity switch.

Pros