Placement & Directivity in the Bass Range

Left-Right:

• Often the only option for smaller events due to venue constraints and stage designs.
• One stack of subwoofers on each side of the stage (usually with the top cabinets stacked on top).

Advantages:
+ Easy to set up
+ Stereo setup possible
+ Simple controlling (e.g., for CSA, see below)
+ Top cabinets are quickly or easily placed at the correct height.
+ Cardioid behavior can be achieved with just one additional subwoofer and controller channel (CSA).
+ Stacks of 3–4 subwoofers or more can be controlled (each subwoofer separately) to vary vertical directivity,
or to attenuate upward acoustic radiation.

Disadvantages:
- So-called "bass alleys / comb filtering" (number of interference nulls increases with frequency)
- Sound is not directional
- Does not "throw" or carry the sound very far.
- No attenuation of the sound pressure level behind the subwoofers.
- Top cabinets are often just placed straight on top due to the stacking feet recesses,
  without any horizontal or vertical tilt.

44Hz, 125Hz

Spaced Subwoofer Array / Straight Line

• Subwoofers placed side-by-side, but with physical gaps between the individual cabinets.
• A spaced array narrows the horizontal coverage compared to a single mono stack.
• The more subwoofers used, the more directional the coverage becomes.

Advantages:
 + CSA (Cardioid) can be utilized
 + Curved/Delayed setups can be used
 + Easy to set up
 + Requires only one controller channel
 + Requires only one amplifier channel
 + High acoustic "throw" / distance coverage
 + No cancellation nulls within the critical frequency range

Disadvantages:
 - Spaced arrays produce cancellation nulls above a certain frequency (depending on the gap distance between subs), similar to L-R setups. 
 - Little to no rear attenuation, and if any, only at higher frequencies; instead, it narrows sideways depending on the array size (especially compared to L-R).
 - Requires space and a certain minimum width in front of the stage.
 - No stereo bass split.

Mono-Cluster Setup

• A mono cluster creates an omnidirectional sphere rather than a directional lobe (compared to a spaced array) but carries further than an L-R setup.
• All subwoofers are placed tightly together in a single row or block.

Advantages:
 + CSA (Cardioid) can be utilized
 + Curved/Delayed setups can be used
 + Easy to set up
 + Requires only one controller channel
 + Requires only one amplifier channel
 + "Throws" further than an L-R setup
 + No cancellation nulls within the critical frequency range
 + No side comb filtering compared to a spaced array, and requires less width.

Disadvantages:
 - No cancellation to the rear, but attenuation to the sides depending on the size of the cluster.
 - Requires space and width in front of the stage.
 - No stereo bass split.
 - Does not carry as far as a spaced array, but offers more homogenous dispersion.
 - To completely control directivity, we would need a cluster size of roughly 10x10 meters (>40Hz).

CSA - Cardioid Subwoofer Array:

• Easy to implement and works exceptionally well.
• Can be used with L-R setups, mono clusters, or spaced arrays (partially applicable to End-Fire as well).
• One out of three subwoofers is completely reversed (facing backwards), inverted, and delayed.
(Caution: Flipping the phase by 180° on the controller often yields a different result than true signal inversion!)
(Delay: Physical depth of the subwoofer [acoustic centers] + approx. 10-20cm)
(The level should also be adjusted, approx. + 3dB)

Advantages:
+ Excellent bass cancellation to the rear
+ Requires only one additional controller path and amplifier channel
+ The reversed subwoofer still adds roughly 1.5dB (instead of 3dB) to the total output
+ Coverage pattern can be slightly shaped via the delay settings (cardioid, hypercardioid...)

Disadvantages:
 - Requires an additional controller channel
 - Looks a bit odd because the rear side of one subwoofer is visible
 - Cable routing can be inconvenient.
 - Requires an additional amplifier channel.

Single stack of 3 subs, L-R setup, spaced array

Directional / Curved Bass-Array

• Subwoofers are arranged in a physical arc, delayed towards the outer edges, or both.

Advantages:
 + Rearward acoustic radiation is well attenuated
 + Coverage can be heavily shaped by delay times, as can the rear attenuation
 + No loss in acoustic output level

Disadvantages:
 - Setup becomes quite large
 - Requires a massive amount of amplifier channels
 - Requires a massive amount of controller channels
 - Must be calculated precisely

Info:
• Can also be achieved without separate controller paths by physically staggering the placement of the subwoofers
+ Requires only a single amplifier and DSP channel
- Requires a massive amount of space
- Must be positioned with absolute accuracy
- Any adjustments always involve heavy lifting and reshuffling

Spaced array delayed, spaced array curved, spaced array delayed and curved

Mono Curved, Endfire curved, Endfire 3 Rows Curved

EFA - End Fire Array

• A highly discussed topic on the internet! ;-)
• Subwoofers are set up similarly to a spaced array, but with additional identical stacks placed directly behind them; the front rows are then delayed.

Advantages:
+ Rearward sound is well attenuated if the delay is set shorter, even when physically curved
+ Gain in total SPL due to the additional subwoofers
+ Highly directional and homogenous dispersion pattern
+ Can partially be combined with L-R setups (inheriting its usual disadvantages)

Disadvantages:
- Requires a lot of physical depth between the stage and the audience
- Requires a large number of subwoofer cabinets
- Requires one dedicated DSP + amplifier channel per subwoofer row/array
- Should preferably be built with 3 or 4 rows of subwoofers rather than just 2
- The more arrays used (rows behind the front line), the more the rear cardioid pattern tends to degrade at higher frequencies
- The more arrays used, the narrower the forward coverage angle becomes at higher frequencies

Endfire 2 Rows, Endfire 3 Rows (precise delay -> not ideal)


Endfire 2 Rows Curved, Endfire 3 Rows Curved