A Double Bass Array (DBA) is a specific method of setting up and matching two (or more) subwoofers in a home cinema setup. A DBA uses four subwoofers. As an audio beginner one could assume that the aim of a bass arrays is to make the house tremble with even more bass power. In fact, this set-up is about something else.
Before we explain the use of a double bass array in practice, it is important to understand why they are used in the first place.
Home cinema sets for surround sound and bass power
When sound waves overlap
Double bass arrays are designed to minimise the influence of certain sound wave effects. Because in the low frequency range these can be treacherous under certain room acoustics conditions. This primarily concerns disrupting super-impositions of directly radiated and reflected sound waves. Because when speakers or their membranes hit sound waves, they are reflected from the ceiling, walls and floor.
Inevitably, directly radiated and reflected sound waves of the same frequency meet. Then there are the overlays – and these can be disruptive. Particularly in the low frequency range, it is audible that certain frequencies are cancelled out or build up, which causes the level to drop or rise. So you may hear a serious rise in the low frequency range at certain places in the room (it booms strongly) – or the bass is cancelled out.
These unwelcome interferences are called room modes or standing waves. They sound particularly long and can therefore superimpose resonances in other frequency ranges. Whether and at which frequencies the interference occurs depends on the room dimensions. The decisive factor is that they only ever occur for certain frequencies.
In our previous article about room modes, we describe this phenomenon of wave physics in detail and present methods for tackling it.
How a double bass array anticipates room modes
A double bass array is a proactive attempt to influence the resonances of the sound waves in such a way that the undesired overlays do not occur in the first place. There are four subwoofers in the room: two at the front and two against the back wall. The subwoofers should be identical in construction in order to achieve identical dispersion characteristics. The four subs reproduce the same signal – with the decisive trick that the rear ones swing to the two front ones with a delay. The delay corresponds exactly to the time required by the sound waves of the front subs to reach the rear wall. The signal is also played back inverted.
Inversion and the precisely adjusted delay cause sound waves in the specific frequency range to be erased before they reach the rear wall. The waves that would lead to room modes are therefore not even reflected. The double bass array prevents problematic overlays.
In a single bass array, subwoofers are not compared. Only two subwoofers are installed at the front. The way it works is therefore fundamentally different. The aim here is not to erase certain reflections, but to create a wavefront and stronger levels in the low frequency range.
Double bass array – not the only remedy against room modes
Double bass arrays are rarely found in home cinema setups. On the one hand, it is a very complex and costly solution. On the other hand, not everyone perceives the room modes as disturbing at all and they can go totally unnoticed. The reason for this is that individual frequencies in movies or music are rarely played back constantly for several seconds. Over-emphasised sounds or bass gaps can usually only be heard for a short moment.
Other solutions to avoid interfering sound overlays include considering the installation of the subwoofer and the influence on the room acoustics.
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Conclusion: an overview of Double Bass Arrays
- A Double Bass Array is a subwoofer arrangement designed to prevent room modes.
- This prevents excessive level drops or rises in certain areas of the room.
- These are caused by superimposed sound waves, especially in the bass range.
- A Double Bass Array consists of four subwoofers: two in the front and two directly opposite each other in the rear of the room.
- By wave delay and inverted dispersion, the rear subwoofers eliminate the sound waves just in front of the wall and thus prevent annoying interference.