Advisor

directional PA subwoofer placement – make optimum use of the power.

 

Summary

Setting up PA subwoofers – what you should bear in mind

Positionierung nah an der Wand vermindert Reflexionen

Indoors, unwanted reflections occur in the bass range. Avoid this by placing the speakers close to the wall or far away from it.

Monocluster protects against extinction

The classic L/R set-up (stereo) has many disadvantages, especially cancellations. Set the subs to one position to prevent this.

Complex setups only with specialist knowledge

Cardioid and Endfire arrays require complex settings and can only be implemented with a DSP controller. Book one of our technicians for this.

At major events, the use of subwoofer arrangements whose directivity is calculated in advance has long been common practice. This technology offers advantages not only for large events, but also for medium-sized sound reinforcement tasks. Given a sufficient stock of loudspeakers and power amplifiers, the targeted and controlled emission of low bass can offer many qualitative advantages with relatively little preparation effort:

  • Interference-related problems in the bass range, such as frequency cancellations and overboosting, can be reduced or completely avoided.
  • In front of the stage or on the dance floor, a higher sound pressure level can be achieved with the available power.
  • By utilizing summation effects, a greater range can be achieved with the same amount of material, which better serves more distant audience locations.
  • Areas outside the audience or dance floor, such as drinks or merchandising stands, can be kept quieter.
  • A better distribution of the subwoofers can help to comply more easily with the maximum permitted peak sound pressure level of 135 dB at bass frequencies in accordance with DIN15905-5.
  • The stage and backstage area is less burdened by sound reinforcement subwoofers, which can reduce feedback problems and provide a better monitor sound.

We will now take a look at the most commonly used subwoofer arrangements and how they work. Combinations of different variants are often possible.

LEFT / RIGHT POSITIONING


Source: eventelevator.de

It is helpful to analyze the “standard” setups often used in bass sound reinforcement, such as L/R or LCR, through simulations in order to become aware of the fundamental challenges.
In the conventional L/R arrangement, which in simulations is aligned towards the audience area (to the right), three lobe-shaped sound propagations with two significant gaps can be recognized. In these gaps, the sound pressure loss can be up to 36 dB due to cancelation. Spectators standing directly in front of the subwoofers or their stacks are exposed to particularly high volumes, while the sound pressure level drops by 18 dB even at a distance of 10 meters. Although the room acoustics sometimes help to alleviate these problems, it is important to realize that such a setup cannot be considered ideal – apart from low-budget events or when structural or visual restrictions do not allow any other option.

LCR – LINEUP / MONOCLUSTER

Source: eventelevator.de

The integration of a central subwoofer does not lead to a significant improvement in the sound reinforcement situation. As can be seen in the simulation (see Figure 2), due to the large spatial distance between the loudspeakers, which is greater than half the wavelength, and the resulting different phase positions of the individual subwoofers, there is a level reduction in the middle area of the front audience area. In addition, noticeably more sound energy is radiated towards the stage.
If only a limited number of subwoofers are available, it may make more sense to position them centrally at a small distance from each other or directly next to or above each other (monocluster). If the distance between the speakers is less than half a wavelength of the relevant frequency (often the crossover frequency), there are no interference effects and the speakers act as a single sound source. One disadvantage of this arrangement, however, is that the audience directly in front of the stage can be exposed to very high sound levels, especially if the entire audience area is to be supplied with sufficient low bass.

LINE ARRANGEMENT (TOOTH SPACE)


Source: eventelevator.de

Extending the set-up with additional speakers along the entire width of the stage results in the familiar “gaps between the teeth” arrangement.
In this configuration, a certain directional effect is recognizable, whereby the audience area is covered relatively evenly across its entire width and depth. In addition, the occurrence of strong level fluctuations due to interference is effectively reduced. However, it is important with this arrangement that the distance between the loudspeakers should be a maximum of half a wavelength. If the gaps between the loudspeakers are too large, many interference maxima and minima occur again.

CARDIOID SUBWOOFER ARRAY (CSA)


Source: eventelevator.de

If the low bass level on stage is problematic, cardioid subwoofer arrays (CSA) offer a solution. The aim of these arrangements is to create a cardioid dispersion pattern for low frequencies, which not only concentrates the sound towards the front but also reduces the sound towards the stage (off-axis area).
Probably the best-known concept is the classic CSA arrangement with three (or more) subwoofers, with the middle subwoofer in the three-box configuration facing the stage. The time difference between the subwoofers radiating forwards and backwards is then adjusted. Usually, a delay is selected that corresponds approximately to the depth of the box used in meters, i.e. around 1 to 3 milliseconds.
As the simulation shows, this results in a clearly cardioid directional characteristic. However, this effect decreases at lower frequencies. However, experimentally increasing the delay time can shift the directivity slightly towards lower frequencies. Many manufacturers also offer special CSA presets in the software of their power amplifiers or controllers. In cases of doubt, these presets should be preferred, as they often contain additional level and frequency response corrections tailored to the specific subwoofer model.

END FIRE ARRAY

Source: eventelevator.de

End-fired arrays are currently in great demand for large sound reinforcement systems. With this technique, several subwoofers are placed one behind the other at a distance of λ/4 (for example at 80 Hz, which corresponds to 1.06 meters) and delayed in time so that they are tuned to the level of the rearmost speaker. The aim is to effectively attenuate the sound to the rear and to amplify the sound pressure along the main axis.
For a setup with four speakers and a target frequency of 80 Hz, the delay times from the front speaker would be: 9.3 ms, 6.2 ms and 3.1 ms. With end-fired arrays, however, it must be noted that the runtime of the actual PA system must be adjusted for very long lines, which can lead to difficulties at live events. With a L/R arrangement of the systems, possible interference cancellations in the middle of the audience area and the high volume load of the audience directly in front of the array must also be taken into account. The level drop of 3 dB per octave along the summing axis can be compensated with an equalizer, similar to the Augspurger CSA, but this is at the expense of the overall performance of the system.

SUMMARY
With all these subwoofer configurations, it is advisable to avoid setups with different speaker types, as correct operation requires identical levels and frequency responses to be maintained. It also makes sense to check the virtually developed set-up variants on site by measuring the phase frequency response and listening carefully at different locations. Based on the results, the positioning of the speakers and the controller settings should then be adjusted if necessary. For those who want to learn more about these and other subwoofer configurations, both in theory and in practice, Markus Zehner’s “Bass Total” seminars (https://www.zehner.ch), which are also held regularly in Germany, are highly recommended. Many manufacturers also offer seminars on this topic. Choosing the right set-up depends on many factors, including the size and shape of the room, the type of event and the equipment available.
Each of these methods has its specific advantages and disadvantages. The decision should therefore always be based on a careful assessment of the specific requirements of each event and the characteristics of the venue. It is also important to note that the quality of the sound does not depend solely on the positioning of the subwoofers, but also on the quality of the subwoofers themselves, their coordination with the overall PA system and the competence of the sound engineer.

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